International Journal of Rheumatic Diseases 2014
ORIGINAL ARTICLE
Population attributable risk from obesity to arthritis in the Canadian Population Health Longitudinal Survey 1994–2006 Frank MO,1 Howard MORRISON,1 and Ineke C. NEUTEL2 1
Social Determinants and Science Integration Directorate, Public Health Agency of Canada, and 2The R. Samuel McLaughlin Centre, Institute of Population Health, University of Ottawa, Ottawa, Ontario, Canada
Abstract Objectives: To examine the relationship, potential associations, and determine the population attributable risk percent (PAR%) between obesity and arthritis in Canadians aged 40 to 79 from 1994 to 2006. Methods: Our study population were the 17 276 respondents in the Canadian National Population Longitudinal Health Survey data, from 1994/1995 to 2006/2007. Results: Respondents who were overweight and obese increased over time, with arthritis increasing from 20% to 30% over the study period. Women reported a 10% higher prevalence of arthritis than men. Men aged 70–79 and women aged 60–69 were most likely to report arthritis. PAR% calculations indicated that 3.8% of arthritis in 1994 and 7.5% in 2006 in the overall population could be attributed to overweight, while the proportion of arthritis attributable to obesity increased from 7.0% in 1994 to 10.2% in 2006. Conclusions: Increasing overweight/obesity of the population was positively associated with arthritis in Canada for both sexes. In addition to the many other beneficial health effects, reducing levels of excess weight may result in either less arthritis or fewer manifestations of symptoms of arthritis or both. Key words: arthritis, Canada, epidemiology, longitudinal health survey, overweight/obesity, PAR%.
INTRODUCTION Arthritis and related conditions affected more than 4.6 million Canadians aged 15 years and older (1/6 people) in 2006. In all age groups, the prevalence of arthritis and related conditions were higher in women than in men; three out of five Canadians with arthritis and related conditions were women.1 In Canada, arthritis carries an economic burden estimated at $4.4 billion, and is one of the most costly of all diseases.2–4 Arthritis is a major cause of pain and disability, especially in elderly people. Using data from the 2000 Canadian Community Health Survey
Correspondence: Dr Frank Mo, Social Determinants and Science Integration Directorate, Public Health Agency of Canada. Ottawa, Ontario, Canada K1A 0K9. Email: [email protected]
and Statistics Canada age projections, it has been estimated that by the year 2021, 20% of Canadians over 15 years, or 6.4 million people, will have arthritis, compared to the 4.6 million persons, or 17% of Canadians estimated for 2006.4,5 There are many forms of arthritis, by far the most prevalent is osteoarthritis, for which symptoms tend to start by age 40 and which is more common in women than in men. The number of hospitalizations for hip replacement in Canada has almost tripled in the last two decades while knee replacements have increased at an even faster rate.6 Given the burden, prevalence and cost of arthritis, finding modifiable risk factors for arthritis is imperative. Arthritis rates have been shown to be higher for people who are overweight or obese.6 Wilkins documented 60% more incident arthritis among obese people and considered obesity to be an important risk factor for developing
© 2014 Asia Pacific League of Associations for Rheumatology and Wiley Publishing Asia Pty Ltd
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arthritis, as do others.7–9 Unfortunately, obesity is increasing in Canada and elsewhere at alarming rates, to the extent that many have called it an obesity epidemic.10,11 Arthritis and obesity are both widespread problems with little indication of abating soon. More population-based information is needed on trends in arthritis in Canada, risk factors for arthritis and their relationship to each other. This knowledge is needed not only to assess needs for health care services, but also to learn about any potential for prevention of the disease, or delaying its development. The objectives for this study are to examine potential associations between overweight/obesity and arthritis in Canada and estimate how much percentage (%) of arthritis should be attributable to overweight/obesity in the Canadian population.
METHODOLOGY Data and materials The source population for this study is the Canadian National Population Health Survey (NPHS) longitudinal panel data, from 1994/1995 (cycle 1) to 2006/2007 (cycle 7) with 17 276 respondents in the survey. The sample design of the survey varies by region and by type of sample unit. The household component is based on the Labour Force Survey frame in most provinces; however, in Quebec, dwellings were selected from those in the L’Enqu^ete Sociale et de Sante. Consequently, the target population is identical to that of the households, including all provinces and territories, excluding those on Canadian Forces bases, on Indian reserves, and in some remote areas. Both of these parent surveys are based on highly complex, heavily stratified, multistage designs. This type of clustered design is ideal for controlling costs when personal interviews are needed, as was the case for cycle 1 of the NPHS.12–14 To cover as much as possible of the Canadian population, separate components of the survey were also carried out in the Territories and in healthcare institutions. In the Territories, a simpler stratified design was used. As well, anticipating the creation of Nunavut, separate strata were formed for each of the future territories, Nunavut and NWT.14 Nearly all respondents were re-interviewed then biennially by telephone except for individuals who did not have a telephone, for whom face-to-face interviews were used. Interviewers were instructed to follow all reasonable strategies to trace people. Response rates were 83.6% from cycle 1, cycle 2 92.8%, cycle 3 88.3%, cycle 4 84.9%, cycle 5 80.8%, cycle 6 77.6% and cycle 7 77.0%.
2
Individuals aged 40–79 were included in this study. Younger persons were added to the population once they became 40 years old and the older respondents were dropped after reaching 80. Accordingly, the total sample was changed from year to year, even though the core of the population was the same people. Background, health-related and lifestyle variables were asked in the interview. Body mass index (BMI) was calculated as shown in Table 1, from weight in kilograms divided by height in metres squared.15
Data analysis We calculated the average annual incidence density and prevalence by age standardization. We estimated the adjusted relative risks (RRs) by several separated Poisson regression models based on presence or absence of self-reported arthritis in exposed and non-exposed to overweight/obesity groups (< 25 of BMI as referent group), with adjustments for age (continuous variable), sex (male as referent group), education, income, partnership status, smoking, alcohol drinking, language (English/French), self-reported health status, urban/ rural status and physical activity. In turn, we calculated BMI by adjusting age, sex and socioeconomic status variables, in order to reduce potential confounders. In cycle 4, the year 2000, NPHS population was used as standard population for the purposes of age standardization. All new cases of arthritis were identified as those who had not reported arthritis in any earlier interview and diagnosed by a physician from their family doctor consultation or from hospitalization, to determine changes in attributes before and after the first reporting of arthritis and to avoid any non-articular pain into our data analysis. They had to be omitted since it was not known whether they would have reported arthritis earlier they had been asked. For each new case, data from four cycles were selected: (i) the cycle before first reporting; (ii) the cycle of first reporting; (iii) the cycle after first reporting; and (iv) the second cycle after first reporting. These four groups were then added together to form a new cohort of 1677 incident arthritis cases. The population attributable risk percent (PAR%) was calculated using the formula: p(RR-1)/(p(RR-1)+1) *100; where p is the proportion of overweight and obesity in the entire population and RR is the relative risk.16–19 The prevalence of risk-affected arthritis was determined by risk factors, BMI categories (overweight and obesity) and weighted for the Canadian population in the year 2000.
International Journal of Rheumatic Diseases 2014
PAR% between obesity and arthritis in Canadians
Table 1 Variables definition and description, NPHS, Canada, 1994–2006 Arthritis
BMI
Health status Income
Education French Smoking Partner Physical activity index
Alcohol
Pain Limitations in activity
Then as part of list of chronic diseases ‘Remember, we’re interested in conditions diagnosed by a health professional. Do you have arthritis or rheumatism?’ for 1994–1998. For this study arthritis and fibromyalgia were combined as one variable. Starting in 2000 the question became ‘Do you have arthritis or rheumatism excluding fibromyalgia?’ with a separate similar question asking about fibromyalgia. For this study fibromyalgia was included with the arthritis variable. Body mass index (BMI) was based on the respondent’s self-reported height and weight and calculated as weight in kilogram divided by height in meters squared. This was categorized as acceptable (BMI < 25.0), overweight (BMI 25–29.99) and obese (BMI 30 and over). Self-reported health was ranked by respondents as excellent, very good, good, fair or poor. Excellent and very good were combined as ‘very good health’ and good, fair and poor as ‘poorer health’. Quartiles of total personal income as obtained in the interview were dichotomized by combining the lower two quartiles to form the lowest income (Less than $25 000/per year) to be compared to the top two as highest income (More than $50 000/per year). Those who completed high school vs. those who did not. Completed the interview in French compared to the other respondents which was nearly all English. Includes yes (current smoker and former smoker) and no (never smoking) Those with a partner included those married or living common law, those without a partner included the single, separated or widowed Physically active are defined as an energy expenditure of at least 3 KKD (kilocalories per kilogram of body weight per day), moderately active corresponds to an energy expenditure between 1.5 and 3 KKD, while physically inactive is defined as less than 1.5 KKD. Alcohol consumption is based on a series of question on how many drinks the person had each day of the week before the interview. These were divided into drinking nine or more drinks per week, versus drinking less. A ‘no’ answer to the question ‘Are you usually free of pain and discomfort?’ was taken as indication that the respondent often suffered pain, which excluded the nonarticular pain. Respondents were asked, ‘Because of a long-term physical or mental condition or a health problem, are you limited in the kind or amount of activity you can do: at home? at school? at work? in other activities?’
RESULTS There were 1677 new cases (2.4% incidence) of arthritis from 1995 to 2006. The overall numbers in the study population increased from 5387 in 1994 to 6077 in 2006 (Table 2). The age-standardized prevalence of people with arthritis increased from 20% to 30% from 1994 to 2006. Arthritis was less prevalent among Table 2 New cases and average annual incidence density for arthritis aged 40–79, NPHS, Canada, 1995–2006
1995–1996 1997–1998 1999–2000 2001–2002 2003–2004 2005–2006 1995–2006
New cases
Accumulated sampling population
%
396 262 322 249 242 206 1677
5579 5775 5920 5896 5912 6077 35 159
3.5 2.3 2.7 2.1 2.0 1.7 2.4
International Journal of Rheumatic Diseases 2014
people of normal weight (16.8%), increasing to 20.0% in the overweight category and further increasing to 27.0% in the obese category in 1994. By 2006, these prevalences had increased to 25.2%, 30.2% and 36.4%, respectively (Table 3). All BMI categories show generally increasing trends in arthritis over the years. Table 3 shows the age-standardized prevalence of arthritis increased with age and over time for both males and females. Females had a higher age-standardized prevalence of arthritis than males (24.1% vs. 14.6% in 1994 and 36.6% vs. 22.7% in 2006); women show a considerably higher prevalence of arthritis than men, for most years as much as 10% higher. For both sexes, across all years of data, the prevalence of arthritis was highest among obese individuals. The group with the most prevalent arthritis are obese women, of whom 45% had arthritis in the last six interview cycles. Men had similar trends in arthritis in the three BMI categories but at a lower level. Arthritis was not evenly distributed among the population when considering variables other than age and
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Sex Age BMI categories
Smoking Partner High school completed Rural Income Inactive French questionnaire
Males Females 40–59 60–79 < 25 25–29.9 ≥ 30 Yes No Yes No Yes No Yes No Lower Top Yes No Yes No
Total
1994
1996
1998
2000 2002
2004
2006
14.6 24.1 13.6 33.7 16.8 20.0 27.0 18.9 19.9 18.4 23.6 20.4 30.0 22.7 19.0 24.1 16.5 20.3 19.7 14.9 21.5 19.6
16.3 30.5 17.0 39.2 21.4 23.8 29.7 22.2 24.1 22.7 26.8 25.4 35.4 23.2 23.8 29.2 20.1 24.1 23.4 18.5 25.6 23.7
17.9 31.3 17.2 41.5 21.1 25.8 31.6 21.4 25.4 22.9 30.7 26.0 42.1 25.4 24.7 33.6 20.5 25.6 24.4 19.8 26.6 24.8
19.1 31.4 17.4 35.0 19.4 23.5 28.8 20.4 23.6 21.4 27.5 25.0 35.1 23.6 22.8 31.2 19.8 23.6 22.3 17.8 24.7 23.0
21.2 34.9 20.6 44.0 23.7 27.8 37.3 27.4 28.4 27.0 31.9 30.1 47.3 31.6 27.4 39.6 25.3 30.4 26.5 22.3 30.1 28.2
22.7 36.6 21.7 45.1 25.2 30.2 36.4 30.2 29.7 28.1 34.6 32.5 52.4 30.9 29.4 42.9 27.1 31.6 28.2 24.5 31.5 29.8
19.7 33.4 19.2 42.6 22.7 26.2 35.2 22.9 27.5 25.0 31.7 28.2 40.1 27.6 26.4 38.0 23.2 28.2 25.1 20.8 28.7 26.7
Table 3 Age-standardized prevalence of arthritis by selected sociodemographic characteristics, NPHS, Canada, 1994– 2006†
†We used Canadian population of 2000 as standardized year, BMI, body mass index.
gender. For example, single people (23.6% in 1994 to 34.6% in 2006) tended to report higher arthritis prevalence than married people (18.4% in 1994 to 28.1% in 2006), as did people who did not complete high school, who lived in rural areas and who had a lower family income. Furthermore, the lower prevalence of arthritis among people who used French in completing the interviews for the NPHS was consistent with lower prevalence of arthritis in the province of Quebec (Table 3).
The results of RRs and 95% confidential interval (95%CI) from Table 4 show that even when adjusted for age, sex and socioeconomic status, the overweight group had about 10–60% greater risk of getting arthritis, and the obese group showed 20–220% greater risk of arthritis compared to the normal weight group (Table 4). The PAR% represents the proportion of arthritis that can be attributed to being overweight or obese when the relationship is causal. The proportion of arthritis
Table 4 Adjusted relative risk (RRs)† and 95% confidential interval (95%CI) for arthritis by sex, age, BMI categories, NPHS, Canada, 1994–2006 1994
Sex‡ Age§ BMI¶
Male Female 40–59 60–79 < 25 25–29.9 ≥3 0
1996
1998
2000
2002
2004
2006
RR
95%CI
RR
95%CI
RR
95%CI
RR
95%CI
RR
95%CI
RR
95%CI
RR
95%CI
1.0 1.8 1.0 2.5 1.0 1.1 1.5
– 1.6–2.1 – 1.9–2.8 – 1.0–1.5 1.3–2.0
1.0 2.2 1.0 2.3 1.0 1.1 1.4
– 1.9–2.5 – 2.0–2.6 – 1.0–1.4 1.2–1.9
1.0 1.8 1.0 2.4 1.0 1.2 1.5
– 1.8–2.4 – 2.0–2.7 – 1.1–1.6 1.3–2.1
1.0 1.9 1.0 2.0 1.0 1.1 1.5
– 1.7–2.2 – 1.8–2.3 – 1.0–1.5 1.2–2.0
1.0 2.1 1.0 2.2 1.0 1.1 1.6
– 1.9–2.4 – 1.9–2.5 – 1.0–1.3 1.2–2.2
1.0 2.2 1.0 2.1 1.0 1.1 1.6
– 1.9–2.4 – 1.8–2.3 – 1.0–1.3 1.2–2.1
1.0 2.1 1.0 2.1 1.0 1.2 1.5
– 1.9–2.4 – 1.8–2.4 – 1.1–1.6 1.2–2.0
†RRs were adjusted by each of the other variables, for example, Sex was controlled by age and BMI, Age was adjusted by BMI and sex and BMI was adjusted by age and sex. ‡Male sex as referent group. §The 40–59 age group as referent age group. ¶BMI (body mass index) < 25 category as referent group.
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International Journal of Rheumatic Diseases 2014
PAR% between obesity and arthritis in Canadians
attributable to overweight grew from 3.8% in 1994 to 7.5% in 2006, while the population attributable risk attributed to obesity increased from 7.0% in 1994 to 10.2% in 2006 (Table 5).
DISCUSSION About one quarter of Canadians aged 40–79 years selfreported having arthritis. The prevalence was higher in women than in men, with about one-third of all women in this age group reporting arthritis, and an even higher proportion among women over 60, among whom nearly half reported arthritis. Obesity was found to be an issue for both new and pre-existing cases of arthritis. The proportion of arthritis attributable to being obese, as determined by the PAR%, ranged from 7.0% in 1994 to 10.2% in 2006 in the overall population. Persons who were both obese and who reported arthritis were more likely to report limitations to their activity, poor health, more pain and have a lower income than those with arthritis alone. In fact, musculoskeletal problems are much more prevalent among obese patients than among people of normal weight. Health studies show that obesity is a strong predictor for osteoarthritis, especially in the knees.19,20 Differences in arthritis prevalence were found to be significantly lower in Quebec than the rest of the country. This was supported by the lower risk of arthritis for Canadians who chose to complete the interview in the French language. This was also found when four different Canadian national surveys were compared.21,22 Lower rates could not be explained by differences in age, sex, BMI or other risk factors. More recently, a Health Canada report indicated an age-sex standardized prevalence of 11.7% for residents of Quebec, aged 15
and over and a rate of 23.3% for Nova Scotia, the highest province.3 Quebec also reported very low knee replacement rates compared to the rest of the country.6 This study found the same higher prevalence of arthritis for females and increasing trend with age as many other studies using a similar definition of arthritis.3,7,8,23,24 These same studies also supported higher rates of arthritis with lower levels of education, lower family income, for singles, people living in rural areas and for smokers. No significant difference was found in the increased physical inactivity related to people with arthritis. On the one hand, excess joint activity could lead to increased osteoarthritis, while on the other hand, people with arthritis may be less active because of pain and discomfort with activity. People who were inactive had increased risk of arthritis, especially when obese or elderly.24–28 Higher arthritis rates were found for overweight and obese persons in this study, as has also been shown by other studies.7–9 The overall prevalence of arthritis was higher with increased weight, newly diagnosed cases were more likely to be overweight or obese before first reporting arthritis and were more likely to stay that way after diagnosis. The PAR for excess weight indicated by the current study would be between 4% and 7% for overweight and 7% and 11% for obese. Expecting a decrease in arthritis prevalence with the removal of obesity as calculated by PAR assumes causality between obesity and arthritis in the sense that the presence of obesity brings about an arthritis which would not have been there otherwise. Most authors tend to suggest that the association between excess weight and arthritis is causal.29–31 The mechanism of the relationship between obesity and arthritis is not clear. It is possible that the metabolic or hormonal changes that
Table 5 Trends in population attributable risk percent (PAR%) for arthritis attributed to being overweight and obese, ages 40–79, NPHS, Canada, 1994–2006 1994
1996
1998
Proportion of weight categories in the Canadian population Normal 44.8 43.6 42.3 Overweight 40.1 40.7 40.0 Obese 15.1 15.7 17.8 Relative risk (RRs) of arthritis by weight† Overweight 1.1 1.1 1.2 Obese 1.5 1.4 1.5 PAR% Overweight 3.8 4.0 7.4 Obese 7.0 6.0 8.2
2000
2002
2004
2006
39.8 40.3 19.8
38.7 41.0 20.3
38.8 39.8 21.4
36.9 40.4 22.7
1.1 1.5
1.1 1.6
1.1 1.6
1.2 1.5
3.8 9.0
3.9 10.8
3.8 11.4
7.5 10.2
†All RRs were adjusted by age, sex and socioeconomic status variables.
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accompany obesity also increase the risk of arthritis. It is also possible that obesity would increase the severity and damage of arthritis and advance the time by which a person would seek medical help for their discomfort, leading to an earlier diagnosis. There are also many other conditions associated with obesity, such as dyslipidemia, gout, obstructive sleep apnea, asthma, diabetes, high blood pressure, and heart disease.32–37 From the literature review, we found some controversy viewpoints on the relationship between obesity and inflammatory arthritis; some reported that obesity was associated with inflammatory arthritis. For example, their results showed the association between BMI and functional disability in a large inception cohort of patients with early inflammatory polyarthritis (IP),38 however, others had contrary research results.39,40 There are important strengths but also some limitations in using the longitudinal NPHS data. Strengths include the longitudinal structure of the survey with interviews every 2 years. The initial cohort was selected to be representative of the Canadian population. Also important is the extensive information available on each respondent for each interview over the many cycles of the survey. There were also some limitations of this data. More precise information on type of arthritis, or body parts most affected by the arthritis would have been valuable. Osteoarthritis is by far the most common of the various types of arthritis, especially at the age range for this study. Thus, the characteristics of the combined arthritis category will be influenced by the large proportion of people with osteoarthritis. Full data were not available for all individuals, as the cohort had people dropping out and being added. Sampling numbers had among them some with repeated measures of the same individuals and some were lost to follow-up over time. Limitations also include the self-reported nature of the information, such as self-reported BMI may not be accurate in measurement of height and weight of the respondents in the survey.
CONCLUSION Both obesity and arthritis are growing in prevalence and represent one of the few clearly negative health trends in older adults today. This problem will be compounded by an aging population and has implications for health planning. In addition to the many other beneficial health effects, reducing levels of excess weight may result in either less arthritis or fewer manifestations of symptoms of arthritis, or both.
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REFERENCES 1 Statistics Canada (2005) The Canadian Community Health Survey 2004–05, Cycle 3.1. December. 2 EBIC (1998) Economic Burden of Illness in Canada. [cited 25 Sep 2011.] Available from URL: http://www.phac-aspc. gc.ca/publicat/ebic-femc98/pdf/ebic1998.pdf. 3 Health Canada (2003) Arthritis in Canada. An Ongoing Challenge. Health Canada, Ottawa. 4 Health Canada. (2002) Economic Burden of Illness in Canada. Public Works and Government Services Canada, Ottawa. 5 Badley EM, Wang PP (1998) Arthritis and the aging population: projections of arthritis prevalence in Canada 1991 to 2031. J Rheumatol 25, 138–44. 6 Millar JW (2002) Hip and knee replacement. Health Rep 14, 37–50. 7 Busija L, Hollingsworth B, Buchbinder R et al. (2007) Role of age, sex, and obesity in the higher prevalence of arthritis among lower socioeconomic groups: a population-based survey. Arthritis Rheum 57, 553–61. 8 Wilkins K (2004) Incident arthritis in relation to excess weight. Health Rep 15, 39–49. 9 Sahyoun NR, Hochberg MC, Helmick CG et al. (1999) Body mass index, weight change, and incidence of selfreported physician-diagnosed arthritis among women. Am J Public Health 89, 391–4. 10 Katzmarzyk PT (2002) The Canadian obesity epidemic, 1985–1998. CMAJ 166, 1039–40. 11 Katzmarzyk PT (2002) The Canadian obesity epidemic: an historical perspective. Obes Res 10, 666–74. 12 Statistics Canada (1994) National population health survey - longitudinal (NPHS). Available from URL: http://www. statcan.gc.ca/cgi-bin/imdb/p2SV.pl?Function=getSurvey& SurvId=3225& SurvVer=0&InstaId=15280&InstaVer=1&S DDS=3225&lang=en&db=imdb&adm=8&dis=2. 13 Statistics Canada (2006) National population health survey - longitudinal (NPHS). Available from URL: http:// www.statcan.gc.ca/cgi-bin/imdb/p2SV.pl?Function=getSur vey&SurvId= 3225& SurvVer=0&InstaId=15280&InstaVer= 7&SDDS=3225&lang=en&db=imdb&adm=8&dis=2. 14 Tambay JL, Catlin G (1995) Sample design of the National Population Health Survey. Health Rep (Statistics Canada, Catalogue 82–003). 7(1), 29–38. 15 World Health Organization (2006) What are overweight and obesity? Factsheet No.311. 16 Colton J (1951) A method of estimating comparative rates from clinical data: applications to cancer of the lung, breast, and cervix. J Natl Cancer Inst 11, 1269. 17 Hennekens CH, Buring JE (1987) Epidemiology in Medicine, 1st edn. Little, Brown and Co., New York, NY. 18 Miettinen OS (1974) Proportion of disease caused or prevented by a given exposure, trait or intervention. Am J Epidemol 99, 325.
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19 Badley EM, Ansari H (2010) Arthritis and arthritis-attributable activity limitations in the United States and Canada: a cross-border comparison. Arthritis Care Res (Hoboken) 62, 308–15. 20 Reynolds SL, McIlvane JM (2009) The impact of obesity and arthritis on active life expectancy in older Americans. Obesity (Silver Spring) 17, 363–9. 21 Wang PP, Badley EM (2003) Consistent low prevalence of arthritis in Quebec: findings from a provincial variation study in Canada based on several Canadian population health surveys. J Rheumatol 30, 126–31. 22 Kopec JA, Rahman MM, Berthelot JM et al. (2007) Descriptive epidemiology of osteoarthritis in British Columbia, Canada. J Rheumatol 34, 386–93. 23 Abell JE, Hootman JM, Zack MM et al. (2005) Physical activity and health related quality of life among people with arthritis. J Epidemiol Community Health 59, 380–5. 24 Shih M, Hootman JM, Kruger J et al. (2002) Physical activity in men and women with arthritis National Health Interview Survey, 2002. Am J Prev Med 30, 385–93. 25 McMillan G, Nichols L (2005) Osteoarthritis and meniscus disorders of the knee as occupational diseases of miners. Occup Environ Med 62, 567–75. 26 Hootman JM, Cheng WY (2009) Psychological distress and fair/poor health among adults with arthritis: state-specific prevalence and correlates of general health status, United States, 2007. Prev Med 49, 209–12. 27 Feinglass J, Nelson C, Lawther T et al. (2003) Chronic joint symptoms and prior arthritis diagnosis in community surveys: implications for arthritis prevalence estimates. Public Health Rep 118, 230–9. 28 Helmick CG, Felson DT, Lawrence RC et al. (2008) National Arthritis Data Workgroup. Estimates of the prevalence of arthritis and other rheumatic conditions in the United States. Part I. Arthritis Rheum 58, 15–25. 29 Felson DT, Anderson JJ, Naimark A et al. (1988) Obesity and knee osteoarthritis: the Framingham Study. Ann Intern Med 109, 18–24.
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30 Coggon D, Reading I, Croft P et al. (2001) Knee osteoarthritis and obesity. Int J Obesity 25, 622–7. 31 Felson DT (1990) The epidemiology of knee osteoarthritis: results from the Framingham Osteoarthritis Study. Semin Arthritis Rheum 20, 42–50. 32 Sutherland ER (2008) Obesity and asthma. Immunol Allergy Clin North Am 28 (3), 589–602. 33 Choi HK, Atkinson K, Karlson EW et al. (2005) Obesity, weight change, hypertension, diuretic use, and risk of gout in men: the health professionals follow-up study. Arch Intern Med 165 (7), 742–8. 34 Poulain M, Doucet M, Major GC et al. (2006) The effect of obesity on chronic respiratory diseases: pathophysiology and therapeutic strategies. CMAJ 174 (9), 1293–9. 35 Neilson A, Schneider H (2005) Obesity and its co-morbidities: Present and future importance on health status in Switzerland. Soz- Pr€aventivmed 50, 78–86. Available from URL: http://www.springerlink.com/content/p6786157712 u0827/fulltext.pdf. 36 Gilmore J (1999) Body mass index and health. (Statistics Canada, Catalogue 82–003) Health Rep 11, 31–43. 37 Peytremann-Bridevaux I, Santos-Eggimann B (2008) Health correlates of overweight and obesity in adults aged 50 years and over: results from the Survey of Health, Ageing and Retirement in Europe (SHARE). Obesity and health in Europeans aged > or = 50 years. Swiss Med Wkly 138, 261–6. 38 Humphreys JH, Verstappen SM, Mirjafari H et al. (2013) Association of morbid obesity with disability in early inflammatory polyarthritis: results from the Norfolk Arthritis Register. Arthritis Care Res (Hoboken) 65 (1), 122– 6. 39 Jhun JY, Yoon BY, Park MK et al. (2013) Obesity aggravates the joint inflammation in a collagen-induced arthritis model through deviation to Th17 differentiation. Exp Mol Med 44 (7), 424–31. 40 EULAR (2013) Annual Congress of the European League Against Rheumatism. June 14, 2013.
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ORIGINAL ARTICLE
Population attributable risk from obesity to arthritis in the Canadian Population Health Longitudinal Survey 1994–2006 Frank MO,1 Howard MORRISON,1 and Ineke C. NEUTEL2 1
Social Determinants and Science Integration Directorate, Public Health Agency of Canada, and 2The R. Samuel McLaughlin Centre, Institute of Population Health, University of Ottawa, Ottawa, Ontario, Canada
Abstract Objectives: To examine the relationship, potential associations, and determine the population attributable risk percent (PAR%) between obesity and arthritis in Canadians aged 40 to 79 from 1994 to 2006. Methods: Our study population were the 17 276 respondents in the Canadian National Population Longitudinal Health Survey data, from 1994/1995 to 2006/2007. Results: Respondents who were overweight and obese increased over time, with arthritis increasing from 20% to 30% over the study period. Women reported a 10% higher prevalence of arthritis than men. Men aged 70–79 and women aged 60–69 were most likely to report arthritis. PAR% calculations indicated that 3.8% of arthritis in 1994 and 7.5% in 2006 in the overall population could be attributed to overweight, while the proportion of arthritis attributable to obesity increased from 7.0% in 1994 to 10.2% in 2006. Conclusions: Increasing overweight/obesity of the population was positively associated with arthritis in Canada for both sexes. In addition to the many other beneficial health effects, reducing levels of excess weight may result in either less arthritis or fewer manifestations of symptoms of arthritis or both. Key words: arthritis, Canada, epidemiology, longitudinal health survey, overweight/obesity, PAR%.
INTRODUCTION Arthritis and related conditions affected more than 4.6 million Canadians aged 15 years and older (1/6 people) in 2006. In all age groups, the prevalence of arthritis and related conditions were higher in women than in men; three out of five Canadians with arthritis and related conditions were women.1 In Canada, arthritis carries an economic burden estimated at $4.4 billion, and is one of the most costly of all diseases.2–4 Arthritis is a major cause of pain and disability, especially in elderly people. Using data from the 2000 Canadian Community Health Survey
Correspondence: Dr Frank Mo, Social Determinants and Science Integration Directorate, Public Health Agency of Canada. Ottawa, Ontario, Canada K1A 0K9. Email: [email protected]
and Statistics Canada age projections, it has been estimated that by the year 2021, 20% of Canadians over 15 years, or 6.4 million people, will have arthritis, compared to the 4.6 million persons, or 17% of Canadians estimated for 2006.4,5 There are many forms of arthritis, by far the most prevalent is osteoarthritis, for which symptoms tend to start by age 40 and which is more common in women than in men. The number of hospitalizations for hip replacement in Canada has almost tripled in the last two decades while knee replacements have increased at an even faster rate.6 Given the burden, prevalence and cost of arthritis, finding modifiable risk factors for arthritis is imperative. Arthritis rates have been shown to be higher for people who are overweight or obese.6 Wilkins documented 60% more incident arthritis among obese people and considered obesity to be an important risk factor for developing
© 2014 Asia Pacific League of Associations for Rheumatology and Wiley Publishing Asia Pty Ltd
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arthritis, as do others.7–9 Unfortunately, obesity is increasing in Canada and elsewhere at alarming rates, to the extent that many have called it an obesity epidemic.10,11 Arthritis and obesity are both widespread problems with little indication of abating soon. More population-based information is needed on trends in arthritis in Canada, risk factors for arthritis and their relationship to each other. This knowledge is needed not only to assess needs for health care services, but also to learn about any potential for prevention of the disease, or delaying its development. The objectives for this study are to examine potential associations between overweight/obesity and arthritis in Canada and estimate how much percentage (%) of arthritis should be attributable to overweight/obesity in the Canadian population.
METHODOLOGY Data and materials The source population for this study is the Canadian National Population Health Survey (NPHS) longitudinal panel data, from 1994/1995 (cycle 1) to 2006/2007 (cycle 7) with 17 276 respondents in the survey. The sample design of the survey varies by region and by type of sample unit. The household component is based on the Labour Force Survey frame in most provinces; however, in Quebec, dwellings were selected from those in the L’Enqu^ete Sociale et de Sante. Consequently, the target population is identical to that of the households, including all provinces and territories, excluding those on Canadian Forces bases, on Indian reserves, and in some remote areas. Both of these parent surveys are based on highly complex, heavily stratified, multistage designs. This type of clustered design is ideal for controlling costs when personal interviews are needed, as was the case for cycle 1 of the NPHS.12–14 To cover as much as possible of the Canadian population, separate components of the survey were also carried out in the Territories and in healthcare institutions. In the Territories, a simpler stratified design was used. As well, anticipating the creation of Nunavut, separate strata were formed for each of the future territories, Nunavut and NWT.14 Nearly all respondents were re-interviewed then biennially by telephone except for individuals who did not have a telephone, for whom face-to-face interviews were used. Interviewers were instructed to follow all reasonable strategies to trace people. Response rates were 83.6% from cycle 1, cycle 2 92.8%, cycle 3 88.3%, cycle 4 84.9%, cycle 5 80.8%, cycle 6 77.6% and cycle 7 77.0%.
2
Individuals aged 40–79 were included in this study. Younger persons were added to the population once they became 40 years old and the older respondents were dropped after reaching 80. Accordingly, the total sample was changed from year to year, even though the core of the population was the same people. Background, health-related and lifestyle variables were asked in the interview. Body mass index (BMI) was calculated as shown in Table 1, from weight in kilograms divided by height in metres squared.15
Data analysis We calculated the average annual incidence density and prevalence by age standardization. We estimated the adjusted relative risks (RRs) by several separated Poisson regression models based on presence or absence of self-reported arthritis in exposed and non-exposed to overweight/obesity groups (< 25 of BMI as referent group), with adjustments for age (continuous variable), sex (male as referent group), education, income, partnership status, smoking, alcohol drinking, language (English/French), self-reported health status, urban/ rural status and physical activity. In turn, we calculated BMI by adjusting age, sex and socioeconomic status variables, in order to reduce potential confounders. In cycle 4, the year 2000, NPHS population was used as standard population for the purposes of age standardization. All new cases of arthritis were identified as those who had not reported arthritis in any earlier interview and diagnosed by a physician from their family doctor consultation or from hospitalization, to determine changes in attributes before and after the first reporting of arthritis and to avoid any non-articular pain into our data analysis. They had to be omitted since it was not known whether they would have reported arthritis earlier they had been asked. For each new case, data from four cycles were selected: (i) the cycle before first reporting; (ii) the cycle of first reporting; (iii) the cycle after first reporting; and (iv) the second cycle after first reporting. These four groups were then added together to form a new cohort of 1677 incident arthritis cases. The population attributable risk percent (PAR%) was calculated using the formula: p(RR-1)/(p(RR-1)+1) *100; where p is the proportion of overweight and obesity in the entire population and RR is the relative risk.16–19 The prevalence of risk-affected arthritis was determined by risk factors, BMI categories (overweight and obesity) and weighted for the Canadian population in the year 2000.
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PAR% between obesity and arthritis in Canadians
Table 1 Variables definition and description, NPHS, Canada, 1994–2006 Arthritis
BMI
Health status Income
Education French Smoking Partner Physical activity index
Alcohol
Pain Limitations in activity
Then as part of list of chronic diseases ‘Remember, we’re interested in conditions diagnosed by a health professional. Do you have arthritis or rheumatism?’ for 1994–1998. For this study arthritis and fibromyalgia were combined as one variable. Starting in 2000 the question became ‘Do you have arthritis or rheumatism excluding fibromyalgia?’ with a separate similar question asking about fibromyalgia. For this study fibromyalgia was included with the arthritis variable. Body mass index (BMI) was based on the respondent’s self-reported height and weight and calculated as weight in kilogram divided by height in meters squared. This was categorized as acceptable (BMI < 25.0), overweight (BMI 25–29.99) and obese (BMI 30 and over). Self-reported health was ranked by respondents as excellent, very good, good, fair or poor. Excellent and very good were combined as ‘very good health’ and good, fair and poor as ‘poorer health’. Quartiles of total personal income as obtained in the interview were dichotomized by combining the lower two quartiles to form the lowest income (Less than $25 000/per year) to be compared to the top two as highest income (More than $50 000/per year). Those who completed high school vs. those who did not. Completed the interview in French compared to the other respondents which was nearly all English. Includes yes (current smoker and former smoker) and no (never smoking) Those with a partner included those married or living common law, those without a partner included the single, separated or widowed Physically active are defined as an energy expenditure of at least 3 KKD (kilocalories per kilogram of body weight per day), moderately active corresponds to an energy expenditure between 1.5 and 3 KKD, while physically inactive is defined as less than 1.5 KKD. Alcohol consumption is based on a series of question on how many drinks the person had each day of the week before the interview. These were divided into drinking nine or more drinks per week, versus drinking less. A ‘no’ answer to the question ‘Are you usually free of pain and discomfort?’ was taken as indication that the respondent often suffered pain, which excluded the nonarticular pain. Respondents were asked, ‘Because of a long-term physical or mental condition or a health problem, are you limited in the kind or amount of activity you can do: at home? at school? at work? in other activities?’
RESULTS There were 1677 new cases (2.4% incidence) of arthritis from 1995 to 2006. The overall numbers in the study population increased from 5387 in 1994 to 6077 in 2006 (Table 2). The age-standardized prevalence of people with arthritis increased from 20% to 30% from 1994 to 2006. Arthritis was less prevalent among Table 2 New cases and average annual incidence density for arthritis aged 40–79, NPHS, Canada, 1995–2006
1995–1996 1997–1998 1999–2000 2001–2002 2003–2004 2005–2006 1995–2006
New cases
Accumulated sampling population
%
396 262 322 249 242 206 1677
5579 5775 5920 5896 5912 6077 35 159
3.5 2.3 2.7 2.1 2.0 1.7 2.4
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people of normal weight (16.8%), increasing to 20.0% in the overweight category and further increasing to 27.0% in the obese category in 1994. By 2006, these prevalences had increased to 25.2%, 30.2% and 36.4%, respectively (Table 3). All BMI categories show generally increasing trends in arthritis over the years. Table 3 shows the age-standardized prevalence of arthritis increased with age and over time for both males and females. Females had a higher age-standardized prevalence of arthritis than males (24.1% vs. 14.6% in 1994 and 36.6% vs. 22.7% in 2006); women show a considerably higher prevalence of arthritis than men, for most years as much as 10% higher. For both sexes, across all years of data, the prevalence of arthritis was highest among obese individuals. The group with the most prevalent arthritis are obese women, of whom 45% had arthritis in the last six interview cycles. Men had similar trends in arthritis in the three BMI categories but at a lower level. Arthritis was not evenly distributed among the population when considering variables other than age and
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Sex Age BMI categories
Smoking Partner High school completed Rural Income Inactive French questionnaire
Males Females 40–59 60–79 < 25 25–29.9 ≥ 30 Yes No Yes No Yes No Yes No Lower Top Yes No Yes No
Total
1994
1996
1998
2000 2002
2004
2006
14.6 24.1 13.6 33.7 16.8 20.0 27.0 18.9 19.9 18.4 23.6 20.4 30.0 22.7 19.0 24.1 16.5 20.3 19.7 14.9 21.5 19.6
16.3 30.5 17.0 39.2 21.4 23.8 29.7 22.2 24.1 22.7 26.8 25.4 35.4 23.2 23.8 29.2 20.1 24.1 23.4 18.5 25.6 23.7
17.9 31.3 17.2 41.5 21.1 25.8 31.6 21.4 25.4 22.9 30.7 26.0 42.1 25.4 24.7 33.6 20.5 25.6 24.4 19.8 26.6 24.8
19.1 31.4 17.4 35.0 19.4 23.5 28.8 20.4 23.6 21.4 27.5 25.0 35.1 23.6 22.8 31.2 19.8 23.6 22.3 17.8 24.7 23.0
21.2 34.9 20.6 44.0 23.7 27.8 37.3 27.4 28.4 27.0 31.9 30.1 47.3 31.6 27.4 39.6 25.3 30.4 26.5 22.3 30.1 28.2
22.7 36.6 21.7 45.1 25.2 30.2 36.4 30.2 29.7 28.1 34.6 32.5 52.4 30.9 29.4 42.9 27.1 31.6 28.2 24.5 31.5 29.8
19.7 33.4 19.2 42.6 22.7 26.2 35.2 22.9 27.5 25.0 31.7 28.2 40.1 27.6 26.4 38.0 23.2 28.2 25.1 20.8 28.7 26.7
Table 3 Age-standardized prevalence of arthritis by selected sociodemographic characteristics, NPHS, Canada, 1994– 2006†
†We used Canadian population of 2000 as standardized year, BMI, body mass index.
gender. For example, single people (23.6% in 1994 to 34.6% in 2006) tended to report higher arthritis prevalence than married people (18.4% in 1994 to 28.1% in 2006), as did people who did not complete high school, who lived in rural areas and who had a lower family income. Furthermore, the lower prevalence of arthritis among people who used French in completing the interviews for the NPHS was consistent with lower prevalence of arthritis in the province of Quebec (Table 3).
The results of RRs and 95% confidential interval (95%CI) from Table 4 show that even when adjusted for age, sex and socioeconomic status, the overweight group had about 10–60% greater risk of getting arthritis, and the obese group showed 20–220% greater risk of arthritis compared to the normal weight group (Table 4). The PAR% represents the proportion of arthritis that can be attributed to being overweight or obese when the relationship is causal. The proportion of arthritis
Table 4 Adjusted relative risk (RRs)† and 95% confidential interval (95%CI) for arthritis by sex, age, BMI categories, NPHS, Canada, 1994–2006 1994
Sex‡ Age§ BMI¶
Male Female 40–59 60–79 < 25 25–29.9 ≥3 0
1996
1998
2000
2002
2004
2006
RR
95%CI
RR
95%CI
RR
95%CI
RR
95%CI
RR
95%CI
RR
95%CI
RR
95%CI
1.0 1.8 1.0 2.5 1.0 1.1 1.5
– 1.6–2.1 – 1.9–2.8 – 1.0–1.5 1.3–2.0
1.0 2.2 1.0 2.3 1.0 1.1 1.4
– 1.9–2.5 – 2.0–2.6 – 1.0–1.4 1.2–1.9
1.0 1.8 1.0 2.4 1.0 1.2 1.5
– 1.8–2.4 – 2.0–2.7 – 1.1–1.6 1.3–2.1
1.0 1.9 1.0 2.0 1.0 1.1 1.5
– 1.7–2.2 – 1.8–2.3 – 1.0–1.5 1.2–2.0
1.0 2.1 1.0 2.2 1.0 1.1 1.6
– 1.9–2.4 – 1.9–2.5 – 1.0–1.3 1.2–2.2
1.0 2.2 1.0 2.1 1.0 1.1 1.6
– 1.9–2.4 – 1.8–2.3 – 1.0–1.3 1.2–2.1
1.0 2.1 1.0 2.1 1.0 1.2 1.5
– 1.9–2.4 – 1.8–2.4 – 1.1–1.6 1.2–2.0
†RRs were adjusted by each of the other variables, for example, Sex was controlled by age and BMI, Age was adjusted by BMI and sex and BMI was adjusted by age and sex. ‡Male sex as referent group. §The 40–59 age group as referent age group. ¶BMI (body mass index) < 25 category as referent group.
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PAR% between obesity and arthritis in Canadians
attributable to overweight grew from 3.8% in 1994 to 7.5% in 2006, while the population attributable risk attributed to obesity increased from 7.0% in 1994 to 10.2% in 2006 (Table 5).
DISCUSSION About one quarter of Canadians aged 40–79 years selfreported having arthritis. The prevalence was higher in women than in men, with about one-third of all women in this age group reporting arthritis, and an even higher proportion among women over 60, among whom nearly half reported arthritis. Obesity was found to be an issue for both new and pre-existing cases of arthritis. The proportion of arthritis attributable to being obese, as determined by the PAR%, ranged from 7.0% in 1994 to 10.2% in 2006 in the overall population. Persons who were both obese and who reported arthritis were more likely to report limitations to their activity, poor health, more pain and have a lower income than those with arthritis alone. In fact, musculoskeletal problems are much more prevalent among obese patients than among people of normal weight. Health studies show that obesity is a strong predictor for osteoarthritis, especially in the knees.19,20 Differences in arthritis prevalence were found to be significantly lower in Quebec than the rest of the country. This was supported by the lower risk of arthritis for Canadians who chose to complete the interview in the French language. This was also found when four different Canadian national surveys were compared.21,22 Lower rates could not be explained by differences in age, sex, BMI or other risk factors. More recently, a Health Canada report indicated an age-sex standardized prevalence of 11.7% for residents of Quebec, aged 15
and over and a rate of 23.3% for Nova Scotia, the highest province.3 Quebec also reported very low knee replacement rates compared to the rest of the country.6 This study found the same higher prevalence of arthritis for females and increasing trend with age as many other studies using a similar definition of arthritis.3,7,8,23,24 These same studies also supported higher rates of arthritis with lower levels of education, lower family income, for singles, people living in rural areas and for smokers. No significant difference was found in the increased physical inactivity related to people with arthritis. On the one hand, excess joint activity could lead to increased osteoarthritis, while on the other hand, people with arthritis may be less active because of pain and discomfort with activity. People who were inactive had increased risk of arthritis, especially when obese or elderly.24–28 Higher arthritis rates were found for overweight and obese persons in this study, as has also been shown by other studies.7–9 The overall prevalence of arthritis was higher with increased weight, newly diagnosed cases were more likely to be overweight or obese before first reporting arthritis and were more likely to stay that way after diagnosis. The PAR for excess weight indicated by the current study would be between 4% and 7% for overweight and 7% and 11% for obese. Expecting a decrease in arthritis prevalence with the removal of obesity as calculated by PAR assumes causality between obesity and arthritis in the sense that the presence of obesity brings about an arthritis which would not have been there otherwise. Most authors tend to suggest that the association between excess weight and arthritis is causal.29–31 The mechanism of the relationship between obesity and arthritis is not clear. It is possible that the metabolic or hormonal changes that
Table 5 Trends in population attributable risk percent (PAR%) for arthritis attributed to being overweight and obese, ages 40–79, NPHS, Canada, 1994–2006 1994
1996
1998
Proportion of weight categories in the Canadian population Normal 44.8 43.6 42.3 Overweight 40.1 40.7 40.0 Obese 15.1 15.7 17.8 Relative risk (RRs) of arthritis by weight† Overweight 1.1 1.1 1.2 Obese 1.5 1.4 1.5 PAR% Overweight 3.8 4.0 7.4 Obese 7.0 6.0 8.2
2000
2002
2004
2006
39.8 40.3 19.8
38.7 41.0 20.3
38.8 39.8 21.4
36.9 40.4 22.7
1.1 1.5
1.1 1.6
1.1 1.6
1.2 1.5
3.8 9.0
3.9 10.8
3.8 11.4
7.5 10.2
†All RRs were adjusted by age, sex and socioeconomic status variables.
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accompany obesity also increase the risk of arthritis. It is also possible that obesity would increase the severity and damage of arthritis and advance the time by which a person would seek medical help for their discomfort, leading to an earlier diagnosis. There are also many other conditions associated with obesity, such as dyslipidemia, gout, obstructive sleep apnea, asthma, diabetes, high blood pressure, and heart disease.32–37 From the literature review, we found some controversy viewpoints on the relationship between obesity and inflammatory arthritis; some reported that obesity was associated with inflammatory arthritis. For example, their results showed the association between BMI and functional disability in a large inception cohort of patients with early inflammatory polyarthritis (IP),38 however, others had contrary research results.39,40 There are important strengths but also some limitations in using the longitudinal NPHS data. Strengths include the longitudinal structure of the survey with interviews every 2 years. The initial cohort was selected to be representative of the Canadian population. Also important is the extensive information available on each respondent for each interview over the many cycles of the survey. There were also some limitations of this data. More precise information on type of arthritis, or body parts most affected by the arthritis would have been valuable. Osteoarthritis is by far the most common of the various types of arthritis, especially at the age range for this study. Thus, the characteristics of the combined arthritis category will be influenced by the large proportion of people with osteoarthritis. Full data were not available for all individuals, as the cohort had people dropping out and being added. Sampling numbers had among them some with repeated measures of the same individuals and some were lost to follow-up over time. Limitations also include the self-reported nature of the information, such as self-reported BMI may not be accurate in measurement of height and weight of the respondents in the survey.
CONCLUSION Both obesity and arthritis are growing in prevalence and represent one of the few clearly negative health trends in older adults today. This problem will be compounded by an aging population and has implications for health planning. In addition to the many other beneficial health effects, reducing levels of excess weight may result in either less arthritis or fewer manifestations of symptoms of arthritis, or both.
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REFERENCES 1 Statistics Canada (2005) The Canadian Community Health Survey 2004–05, Cycle 3.1. December. 2 EBIC (1998) Economic Burden of Illness in Canada. [cited 25 Sep 2011.] Available from URL: http://www.phac-aspc. gc.ca/publicat/ebic-femc98/pdf/ebic1998.pdf. 3 Health Canada (2003) Arthritis in Canada. An Ongoing Challenge. Health Canada, Ottawa. 4 Health Canada. (2002) Economic Burden of Illness in Canada. Public Works and Government Services Canada, Ottawa. 5 Badley EM, Wang PP (1998) Arthritis and the aging population: projections of arthritis prevalence in Canada 1991 to 2031. J Rheumatol 25, 138–44. 6 Millar JW (2002) Hip and knee replacement. Health Rep 14, 37–50. 7 Busija L, Hollingsworth B, Buchbinder R et al. (2007) Role of age, sex, and obesity in the higher prevalence of arthritis among lower socioeconomic groups: a population-based survey. Arthritis Rheum 57, 553–61. 8 Wilkins K (2004) Incident arthritis in relation to excess weight. Health Rep 15, 39–49. 9 Sahyoun NR, Hochberg MC, Helmick CG et al. (1999) Body mass index, weight change, and incidence of selfreported physician-diagnosed arthritis among women. Am J Public Health 89, 391–4. 10 Katzmarzyk PT (2002) The Canadian obesity epidemic, 1985–1998. CMAJ 166, 1039–40. 11 Katzmarzyk PT (2002) The Canadian obesity epidemic: an historical perspective. Obes Res 10, 666–74. 12 Statistics Canada (1994) National population health survey - longitudinal (NPHS). Available from URL: http://www. statcan.gc.ca/cgi-bin/imdb/p2SV.pl?Function=getSurvey& SurvId=3225& SurvVer=0&InstaId=15280&InstaVer=1&S DDS=3225&lang=en&db=imdb&adm=8&dis=2. 13 Statistics Canada (2006) National population health survey - longitudinal (NPHS). Available from URL: http:// www.statcan.gc.ca/cgi-bin/imdb/p2SV.pl?Function=getSur vey&SurvId= 3225& SurvVer=0&InstaId=15280&InstaVer= 7&SDDS=3225&lang=en&db=imdb&adm=8&dis=2. 14 Tambay JL, Catlin G (1995) Sample design of the National Population Health Survey. Health Rep (Statistics Canada, Catalogue 82–003). 7(1), 29–38. 15 World Health Organization (2006) What are overweight and obesity? Factsheet No.311. 16 Colton J (1951) A method of estimating comparative rates from clinical data: applications to cancer of the lung, breast, and cervix. J Natl Cancer Inst 11, 1269. 17 Hennekens CH, Buring JE (1987) Epidemiology in Medicine, 1st edn. Little, Brown and Co., New York, NY. 18 Miettinen OS (1974) Proportion of disease caused or prevented by a given exposure, trait or intervention. Am J Epidemol 99, 325.
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19 Badley EM, Ansari H (2010) Arthritis and arthritis-attributable activity limitations in the United States and Canada: a cross-border comparison. Arthritis Care Res (Hoboken) 62, 308–15. 20 Reynolds SL, McIlvane JM (2009) The impact of obesity and arthritis on active life expectancy in older Americans. Obesity (Silver Spring) 17, 363–9. 21 Wang PP, Badley EM (2003) Consistent low prevalence of arthritis in Quebec: findings from a provincial variation study in Canada based on several Canadian population health surveys. J Rheumatol 30, 126–31. 22 Kopec JA, Rahman MM, Berthelot JM et al. (2007) Descriptive epidemiology of osteoarthritis in British Columbia, Canada. J Rheumatol 34, 386–93. 23 Abell JE, Hootman JM, Zack MM et al. (2005) Physical activity and health related quality of life among people with arthritis. J Epidemiol Community Health 59, 380–5. 24 Shih M, Hootman JM, Kruger J et al. (2002) Physical activity in men and women with arthritis National Health Interview Survey, 2002. Am J Prev Med 30, 385–93. 25 McMillan G, Nichols L (2005) Osteoarthritis and meniscus disorders of the knee as occupational diseases of miners. Occup Environ Med 62, 567–75. 26 Hootman JM, Cheng WY (2009) Psychological distress and fair/poor health among adults with arthritis: state-specific prevalence and correlates of general health status, United States, 2007. Prev Med 49, 209–12. 27 Feinglass J, Nelson C, Lawther T et al. (2003) Chronic joint symptoms and prior arthritis diagnosis in community surveys: implications for arthritis prevalence estimates. Public Health Rep 118, 230–9. 28 Helmick CG, Felson DT, Lawrence RC et al. (2008) National Arthritis Data Workgroup. Estimates of the prevalence of arthritis and other rheumatic conditions in the United States. Part I. Arthritis Rheum 58, 15–25. 29 Felson DT, Anderson JJ, Naimark A et al. (1988) Obesity and knee osteoarthritis: the Framingham Study. Ann Intern Med 109, 18–24.
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30 Coggon D, Reading I, Croft P et al. (2001) Knee osteoarthritis and obesity. Int J Obesity 25, 622–7. 31 Felson DT (1990) The epidemiology of knee osteoarthritis: results from the Framingham Osteoarthritis Study. Semin Arthritis Rheum 20, 42–50. 32 Sutherland ER (2008) Obesity and asthma. Immunol Allergy Clin North Am 28 (3), 589–602. 33 Choi HK, Atkinson K, Karlson EW et al. (2005) Obesity, weight change, hypertension, diuretic use, and risk of gout in men: the health professionals follow-up study. Arch Intern Med 165 (7), 742–8. 34 Poulain M, Doucet M, Major GC et al. (2006) The effect of obesity on chronic respiratory diseases: pathophysiology and therapeutic strategies. CMAJ 174 (9), 1293–9. 35 Neilson A, Schneider H (2005) Obesity and its co-morbidities: Present and future importance on health status in Switzerland. Soz- Pr€aventivmed 50, 78–86. Available from URL: http://www.springerlink.com/content/p6786157712 u0827/fulltext.pdf. 36 Gilmore J (1999) Body mass index and health. (Statistics Canada, Catalogue 82–003) Health Rep 11, 31–43. 37 Peytremann-Bridevaux I, Santos-Eggimann B (2008) Health correlates of overweight and obesity in adults aged 50 years and over: results from the Survey of Health, Ageing and Retirement in Europe (SHARE). Obesity and health in Europeans aged > or = 50 years. Swiss Med Wkly 138, 261–6. 38 Humphreys JH, Verstappen SM, Mirjafari H et al. (2013) Association of morbid obesity with disability in early inflammatory polyarthritis: results from the Norfolk Arthritis Register. Arthritis Care Res (Hoboken) 65 (1), 122– 6. 39 Jhun JY, Yoon BY, Park MK et al. (2013) Obesity aggravates the joint inflammation in a collagen-induced arthritis model through deviation to Th17 differentiation. Exp Mol Med 44 (7), 424–31. 40 EULAR (2013) Annual Congress of the European League Against Rheumatism. June 14, 2013.
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