Menopause: The Journal of The North American Menopause Society Vol. 21, No. 3, pp. 209/210 DOI: 10.1097/gme.0000000000000209 * 2014 by The North American Menopause Society

EDITORIAL Advantages, limitations, and opportunities in the use of national databases n this issue of Menopause, Kang et al1 examined the relationship between employment status and metabolic syndrome in Korea. They defined metabolic syndrome as the presence of three or more of the following: central obesity, elevated blood pressure, impaired glucose tolerance, hypertriglyceridemia, and/or hypocholesterolemia (high-density lipoprotein). After adjusting for age, education level, household income, total daily energy intake, smoking status, alcohol consumption, exercise status, and white blood cell count, they found that postmenopausal women who were unemployed were significantly more likely to meet the criteria for metabolic syndrome than postmenopausal women who were employed full time or part time. Their use of the Korean National Health Examination and Nutrition Survey (KNHANES) demonstrates some of the advantages, limitations, and opportunities associated with the use of large national databases. The KNHANES was designed to assess the prevalence of health conditions in Koreans, as well as their health-related behaviors and nutritional status. Advantages of using national databases include large sample sizes. In this case, data were available for 5,256 Korean women aged 20 to 80 years. These women are representative of the Korean population because of the complex sampling design and the sampling weights assigned to each participant. Another advantage to national databases is that more types of data are available than any single investigator could afford to collect (eg, medical history, lifestyle information, physical examinations, anthropometrics, and biochemical measurements). In this case, data included selfreported lifestyle behaviors and 24-hour dietary recall, along with blood pressure measurements, fasting plasma glucose levels, triglyceride levels, and high-density lipoprotein cholesterol levels. A third advantage is that national databases are often accessible and easy to use. The KNHANES data are free and open to the public.2 A limitation of using national databases is that most are cross-sectional in design. For example, the Korean Ministry of Health and Welfare conducted five cross-sectional KNHANES phases: I (1998), II (2001), III (2005), IV (2007-2009), and V (2010-2012).3 Across waves of data collection, trends in the prevalence of risk factors or diseases can be examined,3 although the study reported here uses only the 2007-2009 survey.1 Because the study is cross-sectional, the authors cannot exclude the possibility that metabolic syndrome caused the unemployment, rather than the other way around. Another limitation is that, despite the breadth of data available, researchers are limited to data that may have been

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collected for reasons unrelated to the purposes of the current investigators. For example, menopause status was based on a self-reported response to the question, BHave you gone through menopause?[ Based on that question, it cannot be known if all postmenopausal women experienced 12 months of amenorrhea. Neither is it possible to assess their age at menopause. Age at menopause is of interest to better understand the risk factors for metabolic syndrome. For example, in the Japan Nurses’ Health Study, women who experienced menopause before age 45 years were more likely to be at risk for hypercholesterolemia.4 Other variables that may have been of interest to this study include household composition and specific leisure activities. The mean age of unemployed premenopausal women was 36.7 years, compared with a mean age of 64.8 years among unemployed postmenopausal women. For both groups, but especially for premenopausal women, the relationship between metabolic syndrome and employment may be complicated by marital status and/or the presence of children in the home. For example, many investigators have found ambulatory blood pressure to be higher at work than at home for men; however, for women, ambulatory blood pressure is influenced as much by stress in the home as by stress experienced at work.5 James6 estimated that women with children experience a 3Ymm Hg increase in both systolic blood pressure and diastolic blood pressure at home for each child. After adjusting for age, body mass index, and position (eg, sitting, standing), Marco et al7 found that women without children in the household had higher diastolic blood pressure in the workplace than at home, whereas women with children did not demonstrate significant differences in blood pressure across sites. In the Korean study presented here, blood pressures were recorded twice at 5-minute intervals and averaged for analysis.1 The effects of children in the household on seated blood pressure measurements, and in relation to the criteria for metabolic syndrome, are not known. Children were not included in the analysis. In this study, exercise was measured using the International Physical Activity Questionnaire short form and was treated as a binary variable. A Bregular exerciser[ was defined as someone who engaged in physical activity of moderate or vigorous intensity 3 days or more per week. Among postmenopausal women, full-time workers had the highest frequency of regular physical activity (37%) compared with unemployed women (32%) and part-time workers (31%). It would have been of interest to explicitly examine time spent watching television or using a computer because the health effects of sedentary behavior are independent of time spent in physical activity.8 Menopause, Vol. 21, No. 3, 2014

Copyright © 2014 The North American Menopause Society. Unauthorized reproduction of this article is prohibited.

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Television viewing and computer use (but not reading) have been associated with an increased risk of metabolic syndrome, especially among women.8 In relation to opportunities, national databases are useful for broad cross-country comparisons if the same variables are measured in each survey. For example, in the US National Health and Nutrition Examination Survey 1999-2002, lower socioeconomic position and lower level of education were associated with a greater likelihood of metabolic syndrome in women aged 26 to 65 years.9 These variables (eg, level of education) are not exactly comparable with the measure of employment status used in the KNHANES; however, both studies suggest that social mechanisms may extend across cultures to influence the risk of metabolic syndrome in women. The contribution of the article presented here is that the association between employment status and metabolic syndrome is separate from the effects of socioeconomic status and lifestyle.1 National databases offer a lowstake means for exploring new directions for research. Financial disclosure/conflicts of interest: None reported.

Lynnette Leidy Sievert, PhD Department of Anthropology University of Massachusetts Amherst Amherst, Massachusetts

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REFERENCES 1. Kang HT, Kim HY, Kim JK, Linton JA, Lee YJ. Employment is associated with a lower prevalence of metabolic syndrome in postmenopausal women, based on the 2007-2009 KNHANES. Menopause 2014;21:221-226. 2. Park HA. The Korea National Health and Nutrition Examination Survey as a primary data source. Korean J Fam Med 2013;34:79. 3. Kang HT, Lee J, Linton JA, Park BJ, Lee YJ. Trends in the prevalence of chronic kidney disease in Korean adults: the Korean National Health and Nutrition Examination Survey from 1998 to 2009. Nephrol Dial Transplant 2013;28:927-936. 4. Lee JS, Hayashi K, Mishra G, Yasui T, Kubota T, Mizunuma H. Independent association between age at natural menopause and hypercholesterolemia, hypertension, and diabetes mellitus: Japan Nurses’ Health Study. J Atheroscler Thromb 2012;20:161-169. 5. James GD, Schlussel YR, Pickering TG. The association between daily blood pressure and catecholamine variability in normotensive working women. Psychosom Med 1993;55:55-60. 6. James GD. Evaluation of journals, diaries, and indexes of work-site and environmental stress. In: White WB, ed. Clinical Hypertension and Vascular Disease: Blood Pressure Monitoring in Cardiovascular Medicine and Therapeutics. Totowa, NJ: Humana Press, 2007:39-58. 7. Marco CA, Schwartz JE, Neal JM, Shiffman S, Catley D, Stone AA. Impact of gender and having children in the household on ambulatory blood pressure in work and nonwork settings: a partial replication and new findings. Ann Behav Med 2000;22:110-115. 8. Bertrais S, Beyeme-Ondoua JP, Czernichow S, Galan P, Hercberg S, Oppert JM. Sedentary behaviors, physical activity, and metabolic syndrome in middle-aged French subjects. Obes Res 2005;13:936-944. 9. Loucks EB, Magnusson KT, Cook S, Rehkopf DH, Ford ES, Berkman LF. Socioeconomic position and the metabolic syndrome in early, middle, and late life: evidence from NHANES 1999-2002. Ann Epidemiol 2007;17:782-790.

* 2014 The North American Menopause Society

Copyright © 2014 The North American Menopause Society. Unauthorized reproduction of this article is prohibited.

Advantages, limitations, and opportunities in the use of national databases.

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