This article was downloaded by: [Tulane University] On: 08 September 2014, At: 10:24 Publisher: Routledge Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Journal of Nutrition in Gerontology and Geriatrics Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/wjne21
Vitamin D Status Is Associated With Grip Strength in Centenarians a
a
Alyson Haslam MS , Mary Ann Johnson PhD , Dorothy B. Hausman a
b
c
PhD , M. Elaine Cress PhD , Denise K. Houston PhD , Adam Davey d
e
PhD , Leonard W. Poon PhD & Georgia Centenarian Study a
Department of Foods and Nutrition , University of Georgia , Athens , Georgia , USA b
Department of Kinesiology , University of Georgia , Athens , Georgia , USA c
Department of Internal Medicine , Wake Forest School of Medicine , Winston-Salem , North Carolina , USA d
Department of Public Health , Temple University , Philadelphia , Pennsylvania , USA e
Institute of Gerontology, College of Public Health , University of Georgia , Athens , Georgia , USA Published online: 05 Mar 2014.
To cite this article: Alyson Haslam MS , Mary Ann Johnson PhD , Dorothy B. Hausman PhD , M. Elaine Cress PhD , Denise K. Houston PhD , Adam Davey PhD , Leonard W. Poon PhD & Georgia Centenarian Study (2014) Vitamin D Status Is Associated With Grip Strength in Centenarians, Journal of Nutrition in Gerontology and Geriatrics, 33:1, 35-46, DOI: 10.1080/21551197.2013.867825 To link to this article: http://dx.doi.org/10.1080/21551197.2013.867825
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content.
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This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/termsand-conditions
Journal of Nutrition in Gerontology and Geriatrics, 33:35–46, 2014 Copyright © Taylor & Francis Group, LLC ISSN: 2155-1197 print/2155-1200 online DOI: 10.1080/21551197.2013.867825
Vitamin D Status Is Associated With Grip Strength in Centenarians ALYSON HASLAM, MS, MARY ANN JOHNSON, PhD, and DOROTHY B. HAUSMAN, PhD
Downloaded by [Tulane University] at 10:24 08 September 2014
Department of Foods and Nutrition, University of Georgia, Athens, Georgia, USA
M. ELAINE CRESS, PhD Department of Kinesiology, University of Georgia, Athens, Georgia, USA
DENISE K. HOUSTON, PhD Department of Internal Medicine, Wake Forest School of Medicine, Winston-Salem, North Carolina, USA
ADAM DAVEY, PhD Department of Public Health, Temple University, Philadelphia, Pennsylvania, USA
LEONARD W. POON, PhD Institute of Gerontology, College of Public Health, University of Georgia, Athens, Georgia, USA
GEORGIA CENTENARIAN STUDY Low serum concentrations of 25-hydroxyvitamin D (25(OH)D) have been associated with poor physical function in older adults, but few, if any, studies have examined this relationship in the very old. Therefore, the purpose of this study is to examine this relationship in the very old. Serum 25(OH)D concentrations were obtained from 194 centenarians and near centenarians (98 years and older). The associations between 25(OH)D concentrations and measures of physical function were evaluated with unadjusted and adjusted regression models. We found that 35% of centenarians had 25(OH)D concentrations less than 50 nmol/L. Adjusted mean grip strength was lower for centenarians with 25(OH)D concentrations less than 75 nmol/L than for centenarians with higher Address correspondence to Mary Ann Johnson, PhD, Department of Foods and Nutrition, University of Georgia, 143 Barrow Hall, Athens, GA 30602, USA. E-mail: drmaryannjohnson@ gmail.com 35
36
A. Haslam et al.
concentrations (P < 0.05). However, there were no differences in the Georgia Centenarian Study (GCS) Composite Scale, a global measure of physical function, between those with higher and lower 25(OH)D concentrations. We conclude that low 25(OH)D concentrations are associated with poor grip strength, but not GCS Composite Scale, in the very old. Considering the high burden of poor physical function in older adults, understanding the relationship between vitamin D and different measures of physical function, including strength, becomes increasingly important.
Downloaded by [Tulane University] at 10:24 08 September 2014
KEYWORDS cross-sectional function, vitamin D
study,
grip
strength,
physical
INTRODUCTION Although the positive effects of vitamin D and calcium on bone health are well established (1), the association between vitamin D and physical function, including muscle strength, has garnered much interest in recent years. However, few studies, if any, have examined this association exclusively in the oldest of old. Studies have shown that older adults (65 years and older) with lower concentrations of vitamin D are more likely to be frail (2, 3) and have poorer physical function (4) than those with higher concentrations. In addition, longitudinal studies have shown that older adults with low 25(OH) D concentrations were more likely to develop mobility limitation and disability than those with adequate concentrations (5–8). While some of these studies have not examined the relationship of vitamin D and muscle strength specifically, muscle strength has been found to be associated with disability and functional limitations (9). The prevalence of individuals older than 70 years at risk of being vitamin D insufficient (25(OH)D < 50 nmol/L) was reported to be 31% and 38% for males and females, respectively (10), but has been found to be as high as 60% and 30%, respectively, for Black and White centenarians when using a definition of 25(OH)D 25–50 nmol/L (11). Decreasing strength and, consequently, functional performance, is also a concern as people age. Decreased grip strength has been found to be a predictor of functional limitations, disability, cognitive decline, and increased mortality in prospective studies (12–14). Considering the high prevalence of vitamin D insufficiency and the decline in physical function as people age, the relationship of vitamin D insufficiency and functional performance and muscle strength warrants a more focused examination in the oldest old. Therefore, the purpose of these secondary analyses is to examine the relationship between vitamin D and selected measures of physical function, including grip strength, in a population-based sample of centenarians and near centenarians (98 years and older).
Vitamin D Associated With Grip in Centenarians
37
METHODS Study Population
Downloaded by [Tulane University] at 10:24 08 September 2014
Study participants were part of the Georgia Centenarian Study, a population-based, multidisciplinary study, which included 244 centenarians and near centenarians (98 years and older) in 44 counties of northern Georgia. Between 2002 and 2005, participants were recruited from the community, personal care homes, and skilled nursing facilities (15). Sampling procedures and data collection have been detailed previously (15, 16). Participants provided written informed consent, and all protocols were approved by the University of Georgia Institutional Review Board on Human Subjects.
Serum 25-Hydroxyvitamin D Serum 25(OH)D concentrations were measured in nonfasting blood samples by radioimmunoassay (RIA kit, Diasorin Laboratories, Stillwater, MN, USA), similar to the method used in National Health and Nutrition Examination Survey III (17). Both D2 and D3 are measured with this method, and consequently assess vitamin D concentrations obtained through diet, dietary supplements and fortified foods, and sunlight exposure (18). The inter-assay and intra-assay coefficients of variation for 25(OH)D were 9.2% to 9.5% and 3.8% to 8.0%, respectively. Serum 25(OH)D concentrations were categorized as < 50 nmol/L (considered insufficient by the Institute of Medicine [1]), 50 to < 75 nmol/L, and ≥ 75 nmol/L (considered sufficient by the Endocrine Society [19, 20]). The relationship of functional status with 25(OH)D concentrations in the deficient range ( 0.97 with values obtained from each hand). Grip strength in the centenarian population has been shown to be moderately correlated with leg strength (r = 0.406), Short Performance Physical Battery (r = 0.461), and the Georgia Centenarian Study Composite Scale (r = 0.613; 21).
Functional Performance The methods used to derive the Georgia Centenarian Study (GCS) Composite Scale are published elsewhere (21). The GCS Composite Scale has been
Downloaded by [Tulane University] at 10:24 08 September 2014
38
A. Haslam et al.
shown to have better concurrent validity with basic and instrumental activities of daily living, leg strength, and grip strength than the Short Performance Physical Battery in centenarians (21). Briefly, it includes timed ability to complete a 2.44-meter walk, 3 balance tasks, and 5 chair rises; ability to complete, with or without assistance, the following tasks: moving from a lying to sitting position, a bed-to-chair transfer, and stepping up one step; and grip strength (any force generation). The participant’s ability was estimated as a z score from the difficulty of each test item and participants’ responses to them. Nonperformers were assigned a score of 1 and the performers were rescaled on a 2- to 12-point scale, with higher scores indicating higher physical function. Functional performance in centenarians can be difficult to assess due to the floor and ceiling effects that are common with traditional measures of functional performance. The GCS Composite Scale captures a broader range of functional performance than other measures of physical function among the oldest of old.
Covariates Demographic covariates included sex (male vs. female), race (Black vs. White), and living arrangements (community/personal care homes vs. nursing homes). Information about disease diagnoses across a variety of organ systems was obtained from self-report (n = 38, 15.6%), proxy report (n = 119, 48.8%), health care professionals (n = 12, 4.9%), or medical records (n = 138, 56.6%). Since a higher number of comorbidities have been shown to be associated with lower levels of functional performance in individuals (22), the sum of disease conditions (congestive heart failure, cerebrovascular disease, chronic obstructive pulmonary disease, and arthritis), present at time of interview, was included as a covariate. Creatinine, hemoglobin, and albumin concentrations, which were used as surrogate measures of disease status, were analyzed at an independent laboratory (Lab Corp, Burlington, North Carolina, USA). Both the interview date and blood draw were recorded and used to determine the season of draw. For these analyses, season was a dichotomous variable (winter vs. nonwinter months, where winter was the months of December, January, and February). Cognition was assessed with the Mini-Mental State Exam (MMSE). Body mass index (BMI) was calculated by taking the weight (kg) divided by height (m)2 from measured height and weight or from medical charts or self-report. Multivitamin supplementation was a dichotomous variable (whether or not a participant was taking any multivitamin supplement at time of interview).
Exclusions A total of 244 centenarians and near centenarians were included in the Georgia Centenarian Study, but those missing data for key variables were
Vitamin D Associated With Grip in Centenarians
39
excluded from the present analyses, resulting in 194 included participants. Participants with missing information were excluded in the following order: missing information for 25(OH)D (n = 7), grip strength (n = 1), creatinine, albumin and/or hemoglobin concentrations (n = 13), arthritis (n = 23), and BMI (n = 6).
Downloaded by [Tulane University] at 10:24 08 September 2014
Statistical Analyses Chi-square and Wilcoxon-Rank Sum analysis were used to determine differences in descriptive characteristics by vitamin D status among centenarians. Analysis of Covariance was used to determine differences in the unadjusted and adjusted means of grip strength and GCS Composite Scale. For each of the analyses, model one included sex, race, and living arrangements as covariates. Model two included those variables in model one plus season, multivitamin use, and BMI. Model three included variables in model two plus creatinine, hemoglobin, and albumin concentrations, MMSE, and the number of comorbidities the individual had at time of interview. Tukey’s multiple comparison test was used to detect differences in adjusted 25(OH) D concentrations for the different classifications. In addition, these analyses were performed using 25(OH)D cut-off points of 50 nmol/L and 75 nmol/L based on recommendations in the literature (1, 20). As a sensitivity analyses, we also repeated analyses including those with missing disease covariates (N = 233). Statistical analysis was performed using SAS software (version 9.1; SAS Institute, Cary, North Carolina, USA), and P value less than 0.05 was considered statistically significant. Relevant model assumptions (e.g., link test, Hosmer-Lemeshov test, linearity of associations) were met for all models.
RESULTS Compared to those who were included, excluded participants were older (101.8 vs. 100.3, P < 0.0001), had lower grip strength (3.3 kg vs. 12.1 kg, P < 0.0001), and were less likely to be White (58.0% vs. 84.0%, P = 0.004) or reside in the community (32.0% vs. 63.4%, P < 0.0001). Excluded participants were also more likely to have vitamin D insufficiency (< 50 nmol/L; 52.0% vs. 35.0%, P = 0.03) than included participants, but did not differ significantly in mean 25(OH)D concentration (59.3 nmol/L vs. 68.4 nmol/L, P = 0.13). In these analyses, 82.5% of participants (n = 160) were female, 84% were White (n = 163), and 36.6 % resided in a nursing home (n = 71). Overall, mean age was 100.3 years, 25(OH)D concentration was 68.4 nmol/L, and average grip strength was 12.1 kg. Table 1 shows the descriptive characteristics of the included participants by vitamin D status. Sixty-eight (35.1%)
40
A. Haslam et al.
TABLE 1 Selected Participant Characteristics by Vitamin D Status in Centenarians1 Serum 25OHD (nmol/L)
Downloaded by [Tulane University] at 10:24 08 September 2014
< 50 N Age, mean (SD) Gender, % (n) Male Female Race, % (n) White Black Living arrangements, % (n) Community/personal care home Nursing home Season (winter), % (n) 25-hydroxyvitamin D, nmol/L, mean (SD) Body mass index, kg/m2, mean (SD) Congestive heart failure, % (n) Chronic obstructive pulmonary disease, % (n) Arthritis, % (n) Creatinine, mg/dL, mean (SD) Hemoglobin, g/dL, mean (SD) Albumin, g/dL, mean (SD) Mini Mental State Exam score, mean (SD) Grip strength in men, kg Mean (SD) N Grip strength in women, kg Mean (SD) N Low grip strength, ≤ 25th percentile (gender specific), % (n) Georgia Centenarian Study Composite Scale, mean (SD)
50 to
Journal of Nutrition in Gerontology and Geriatrics Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/wjne21
Vitamin D Status Is Associated With Grip Strength in Centenarians a
a
Alyson Haslam MS , Mary Ann Johnson PhD , Dorothy B. Hausman a
b
c
PhD , M. Elaine Cress PhD , Denise K. Houston PhD , Adam Davey d
e
PhD , Leonard W. Poon PhD & Georgia Centenarian Study a
Department of Foods and Nutrition , University of Georgia , Athens , Georgia , USA b
Department of Kinesiology , University of Georgia , Athens , Georgia , USA c
Department of Internal Medicine , Wake Forest School of Medicine , Winston-Salem , North Carolina , USA d
Department of Public Health , Temple University , Philadelphia , Pennsylvania , USA e
Institute of Gerontology, College of Public Health , University of Georgia , Athens , Georgia , USA Published online: 05 Mar 2014.
To cite this article: Alyson Haslam MS , Mary Ann Johnson PhD , Dorothy B. Hausman PhD , M. Elaine Cress PhD , Denise K. Houston PhD , Adam Davey PhD , Leonard W. Poon PhD & Georgia Centenarian Study (2014) Vitamin D Status Is Associated With Grip Strength in Centenarians, Journal of Nutrition in Gerontology and Geriatrics, 33:1, 35-46, DOI: 10.1080/21551197.2013.867825 To link to this article: http://dx.doi.org/10.1080/21551197.2013.867825
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content.
Downloaded by [Tulane University] at 10:24 08 September 2014
This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/termsand-conditions
Journal of Nutrition in Gerontology and Geriatrics, 33:35–46, 2014 Copyright © Taylor & Francis Group, LLC ISSN: 2155-1197 print/2155-1200 online DOI: 10.1080/21551197.2013.867825
Vitamin D Status Is Associated With Grip Strength in Centenarians ALYSON HASLAM, MS, MARY ANN JOHNSON, PhD, and DOROTHY B. HAUSMAN, PhD
Downloaded by [Tulane University] at 10:24 08 September 2014
Department of Foods and Nutrition, University of Georgia, Athens, Georgia, USA
M. ELAINE CRESS, PhD Department of Kinesiology, University of Georgia, Athens, Georgia, USA
DENISE K. HOUSTON, PhD Department of Internal Medicine, Wake Forest School of Medicine, Winston-Salem, North Carolina, USA
ADAM DAVEY, PhD Department of Public Health, Temple University, Philadelphia, Pennsylvania, USA
LEONARD W. POON, PhD Institute of Gerontology, College of Public Health, University of Georgia, Athens, Georgia, USA
GEORGIA CENTENARIAN STUDY Low serum concentrations of 25-hydroxyvitamin D (25(OH)D) have been associated with poor physical function in older adults, but few, if any, studies have examined this relationship in the very old. Therefore, the purpose of this study is to examine this relationship in the very old. Serum 25(OH)D concentrations were obtained from 194 centenarians and near centenarians (98 years and older). The associations between 25(OH)D concentrations and measures of physical function were evaluated with unadjusted and adjusted regression models. We found that 35% of centenarians had 25(OH)D concentrations less than 50 nmol/L. Adjusted mean grip strength was lower for centenarians with 25(OH)D concentrations less than 75 nmol/L than for centenarians with higher Address correspondence to Mary Ann Johnson, PhD, Department of Foods and Nutrition, University of Georgia, 143 Barrow Hall, Athens, GA 30602, USA. E-mail: drmaryannjohnson@ gmail.com 35
36
A. Haslam et al.
concentrations (P < 0.05). However, there were no differences in the Georgia Centenarian Study (GCS) Composite Scale, a global measure of physical function, between those with higher and lower 25(OH)D concentrations. We conclude that low 25(OH)D concentrations are associated with poor grip strength, but not GCS Composite Scale, in the very old. Considering the high burden of poor physical function in older adults, understanding the relationship between vitamin D and different measures of physical function, including strength, becomes increasingly important.
Downloaded by [Tulane University] at 10:24 08 September 2014
KEYWORDS cross-sectional function, vitamin D
study,
grip
strength,
physical
INTRODUCTION Although the positive effects of vitamin D and calcium on bone health are well established (1), the association between vitamin D and physical function, including muscle strength, has garnered much interest in recent years. However, few studies, if any, have examined this association exclusively in the oldest of old. Studies have shown that older adults (65 years and older) with lower concentrations of vitamin D are more likely to be frail (2, 3) and have poorer physical function (4) than those with higher concentrations. In addition, longitudinal studies have shown that older adults with low 25(OH) D concentrations were more likely to develop mobility limitation and disability than those with adequate concentrations (5–8). While some of these studies have not examined the relationship of vitamin D and muscle strength specifically, muscle strength has been found to be associated with disability and functional limitations (9). The prevalence of individuals older than 70 years at risk of being vitamin D insufficient (25(OH)D < 50 nmol/L) was reported to be 31% and 38% for males and females, respectively (10), but has been found to be as high as 60% and 30%, respectively, for Black and White centenarians when using a definition of 25(OH)D 25–50 nmol/L (11). Decreasing strength and, consequently, functional performance, is also a concern as people age. Decreased grip strength has been found to be a predictor of functional limitations, disability, cognitive decline, and increased mortality in prospective studies (12–14). Considering the high prevalence of vitamin D insufficiency and the decline in physical function as people age, the relationship of vitamin D insufficiency and functional performance and muscle strength warrants a more focused examination in the oldest old. Therefore, the purpose of these secondary analyses is to examine the relationship between vitamin D and selected measures of physical function, including grip strength, in a population-based sample of centenarians and near centenarians (98 years and older).
Vitamin D Associated With Grip in Centenarians
37
METHODS Study Population
Downloaded by [Tulane University] at 10:24 08 September 2014
Study participants were part of the Georgia Centenarian Study, a population-based, multidisciplinary study, which included 244 centenarians and near centenarians (98 years and older) in 44 counties of northern Georgia. Between 2002 and 2005, participants were recruited from the community, personal care homes, and skilled nursing facilities (15). Sampling procedures and data collection have been detailed previously (15, 16). Participants provided written informed consent, and all protocols were approved by the University of Georgia Institutional Review Board on Human Subjects.
Serum 25-Hydroxyvitamin D Serum 25(OH)D concentrations were measured in nonfasting blood samples by radioimmunoassay (RIA kit, Diasorin Laboratories, Stillwater, MN, USA), similar to the method used in National Health and Nutrition Examination Survey III (17). Both D2 and D3 are measured with this method, and consequently assess vitamin D concentrations obtained through diet, dietary supplements and fortified foods, and sunlight exposure (18). The inter-assay and intra-assay coefficients of variation for 25(OH)D were 9.2% to 9.5% and 3.8% to 8.0%, respectively. Serum 25(OH)D concentrations were categorized as < 50 nmol/L (considered insufficient by the Institute of Medicine [1]), 50 to < 75 nmol/L, and ≥ 75 nmol/L (considered sufficient by the Endocrine Society [19, 20]). The relationship of functional status with 25(OH)D concentrations in the deficient range ( 0.97 with values obtained from each hand). Grip strength in the centenarian population has been shown to be moderately correlated with leg strength (r = 0.406), Short Performance Physical Battery (r = 0.461), and the Georgia Centenarian Study Composite Scale (r = 0.613; 21).
Functional Performance The methods used to derive the Georgia Centenarian Study (GCS) Composite Scale are published elsewhere (21). The GCS Composite Scale has been
Downloaded by [Tulane University] at 10:24 08 September 2014
38
A. Haslam et al.
shown to have better concurrent validity with basic and instrumental activities of daily living, leg strength, and grip strength than the Short Performance Physical Battery in centenarians (21). Briefly, it includes timed ability to complete a 2.44-meter walk, 3 balance tasks, and 5 chair rises; ability to complete, with or without assistance, the following tasks: moving from a lying to sitting position, a bed-to-chair transfer, and stepping up one step; and grip strength (any force generation). The participant’s ability was estimated as a z score from the difficulty of each test item and participants’ responses to them. Nonperformers were assigned a score of 1 and the performers were rescaled on a 2- to 12-point scale, with higher scores indicating higher physical function. Functional performance in centenarians can be difficult to assess due to the floor and ceiling effects that are common with traditional measures of functional performance. The GCS Composite Scale captures a broader range of functional performance than other measures of physical function among the oldest of old.
Covariates Demographic covariates included sex (male vs. female), race (Black vs. White), and living arrangements (community/personal care homes vs. nursing homes). Information about disease diagnoses across a variety of organ systems was obtained from self-report (n = 38, 15.6%), proxy report (n = 119, 48.8%), health care professionals (n = 12, 4.9%), or medical records (n = 138, 56.6%). Since a higher number of comorbidities have been shown to be associated with lower levels of functional performance in individuals (22), the sum of disease conditions (congestive heart failure, cerebrovascular disease, chronic obstructive pulmonary disease, and arthritis), present at time of interview, was included as a covariate. Creatinine, hemoglobin, and albumin concentrations, which were used as surrogate measures of disease status, were analyzed at an independent laboratory (Lab Corp, Burlington, North Carolina, USA). Both the interview date and blood draw were recorded and used to determine the season of draw. For these analyses, season was a dichotomous variable (winter vs. nonwinter months, where winter was the months of December, January, and February). Cognition was assessed with the Mini-Mental State Exam (MMSE). Body mass index (BMI) was calculated by taking the weight (kg) divided by height (m)2 from measured height and weight or from medical charts or self-report. Multivitamin supplementation was a dichotomous variable (whether or not a participant was taking any multivitamin supplement at time of interview).
Exclusions A total of 244 centenarians and near centenarians were included in the Georgia Centenarian Study, but those missing data for key variables were
Vitamin D Associated With Grip in Centenarians
39
excluded from the present analyses, resulting in 194 included participants. Participants with missing information were excluded in the following order: missing information for 25(OH)D (n = 7), grip strength (n = 1), creatinine, albumin and/or hemoglobin concentrations (n = 13), arthritis (n = 23), and BMI (n = 6).
Downloaded by [Tulane University] at 10:24 08 September 2014
Statistical Analyses Chi-square and Wilcoxon-Rank Sum analysis were used to determine differences in descriptive characteristics by vitamin D status among centenarians. Analysis of Covariance was used to determine differences in the unadjusted and adjusted means of grip strength and GCS Composite Scale. For each of the analyses, model one included sex, race, and living arrangements as covariates. Model two included those variables in model one plus season, multivitamin use, and BMI. Model three included variables in model two plus creatinine, hemoglobin, and albumin concentrations, MMSE, and the number of comorbidities the individual had at time of interview. Tukey’s multiple comparison test was used to detect differences in adjusted 25(OH) D concentrations for the different classifications. In addition, these analyses were performed using 25(OH)D cut-off points of 50 nmol/L and 75 nmol/L based on recommendations in the literature (1, 20). As a sensitivity analyses, we also repeated analyses including those with missing disease covariates (N = 233). Statistical analysis was performed using SAS software (version 9.1; SAS Institute, Cary, North Carolina, USA), and P value less than 0.05 was considered statistically significant. Relevant model assumptions (e.g., link test, Hosmer-Lemeshov test, linearity of associations) were met for all models.
RESULTS Compared to those who were included, excluded participants were older (101.8 vs. 100.3, P < 0.0001), had lower grip strength (3.3 kg vs. 12.1 kg, P < 0.0001), and were less likely to be White (58.0% vs. 84.0%, P = 0.004) or reside in the community (32.0% vs. 63.4%, P < 0.0001). Excluded participants were also more likely to have vitamin D insufficiency (< 50 nmol/L; 52.0% vs. 35.0%, P = 0.03) than included participants, but did not differ significantly in mean 25(OH)D concentration (59.3 nmol/L vs. 68.4 nmol/L, P = 0.13). In these analyses, 82.5% of participants (n = 160) were female, 84% were White (n = 163), and 36.6 % resided in a nursing home (n = 71). Overall, mean age was 100.3 years, 25(OH)D concentration was 68.4 nmol/L, and average grip strength was 12.1 kg. Table 1 shows the descriptive characteristics of the included participants by vitamin D status. Sixty-eight (35.1%)
40
A. Haslam et al.
TABLE 1 Selected Participant Characteristics by Vitamin D Status in Centenarians1 Serum 25OHD (nmol/L)
Downloaded by [Tulane University] at 10:24 08 September 2014
< 50 N Age, mean (SD) Gender, % (n) Male Female Race, % (n) White Black Living arrangements, % (n) Community/personal care home Nursing home Season (winter), % (n) 25-hydroxyvitamin D, nmol/L, mean (SD) Body mass index, kg/m2, mean (SD) Congestive heart failure, % (n) Chronic obstructive pulmonary disease, % (n) Arthritis, % (n) Creatinine, mg/dL, mean (SD) Hemoglobin, g/dL, mean (SD) Albumin, g/dL, mean (SD) Mini Mental State Exam score, mean (SD) Grip strength in men, kg Mean (SD) N Grip strength in women, kg Mean (SD) N Low grip strength, ≤ 25th percentile (gender specific), % (n) Georgia Centenarian Study Composite Scale, mean (SD)
50 to
