DOI: 10.2337/dc06-1400 © 2007 by the American Diabetes Association
The Effect of Menopause on the Metabolic Syndrome Among Korean WomenThe Korean National Health and Nutrition Examination Survey, 2001
1 Korean Association of Public Health Doctor, Chungcheongbuk-do, Korea Address correspondence and reprint requests to Jong Park, MD, PhD, Department of Preventive Medicine, College of Medicine, Chosun University, 375 Seoseok-dong, Dong-gu, Gwangju, 501-759, Korea. E-mail: jpark{at}chosun.ac.kr
OBJECTIVEThis study examined the effect of menopausal status on the risk of the metabolic syndrome in Korean women. RESEARCH DESIGN AND METHODSData were obtained from the Korean National Health and Nutrition Examination Survey of 2001. A total of 2,671 women who did not receive hormone replacement therapy (1,893 premenopausal women and 778 postmenopausal women) were included in the analysis. The metabolic syndrome was defined according to the National Cholesterol Education Program Adult Treatment Panel III. RESULTSPostmenopausal women had significantly higher mean waist circumference, systolic blood pressure, pulse pressure, total cholesterol, LDL cholesterol, and triglyceride levels than premenopausal women after adjusting for age (P = 0.018, P = 0.001, P < 0.0001, P < 0.0001, P < 0.0001, and P = 0.006, respectively). Among postmenopausal women, the age-adjusted odds ratio was 1.61 (95% CI 1.152.25) for abdominal obesity, 1.11 (0.761.61) for elevated blood pressure, 1.24 (0.901.72) for low HDL cholesterol, 1.28 (0.891.83) for high triglycerides, and 1.07 (0.691.65) for high fasting glucose compared with premenopausal women. The multivariate-adjusted odds ratio for the metabolic syndrome was 1.60 (95% CI 1.042.46) among postmenopausal women compared with premenopausal women. CONCLUSIONSPostmenopausal status is associated with an increased risk of the metabolic syndrome independent of normal aging in Korean women.
Abbreviations: CVD, cardiovascular disease HRT, hormone replacement therapy KNHANES, Korean National Health and Nutrition Examination Survey
Stroke and coronary artery disease were major causes of death among Korean women in 2004, second only to malignant diseases (1). Ischemic heart disease is more common in Korean women aged >50 years than in Korean men of the same age-group (2). Menopause appears to increase the risk of cardiovascular disease (CVD) independently of normal aging, and premenopausal women may be protected against CVD compared with men and postmenopausal women of a similar age (3).
The metabolic syndrome is one of the major predisposing factors for CVD, and the population-attributable fraction of the metabolic syndrome has been reported to be 1217% for CVD in the U.S. (4). The prevalence of the metabolic syndrome increases with age in both men and women. From young ( To our knowledge, there have been few studies on the effect of menopause on the development of the metabolic syndrome independent of age, and little information is available on an association between the metabolic syndrome and menopausal status in Korean women. This study examined the difference in the prevalence of the cardiovascular risk factors between postmenopausal and premenopausal women and assessed the effect of menopausal status on the metabolic syndrome in Korean women.
The Korean National Health and Nutrition Examination Survey (KNHANES) was conducted by the Korean Ministry of Health and Welfare in 2001. The participants were noninstitutionalized civilians in the Republic of Korea. The sampling units were households selected through a stratified, multistage, probability-sampling design. The participants completed three parts of a questionnaire, which consisted of a health interview survey, a health behavior survey, and a nutrition survey. A selected sample of participants underwent a health examination survey that included anthropometric measurements, blood pressure measurements, and blood biochemistry tests. Of 12,647 participants aged 10 years, 9,770 (77.3%) attended the health examination survey. Participants aged <20 years were excluded from our analysis, leaving 6,015 participants (2,596 men and 3,419 women). Participants who had one or more missing values of the risk factors necessary for a diagnosis of the metabolic syndrome were also excluded. Ultimately, a total of 5,588 (92.9%) participants (2,369 men and 3,219 women) were included to examine the prevalence of the metabolic syndrome. For the analysis of the effect of menopause, 548 of 3,219 women were excluded for the following reasons: missing data on a questionnaire regarding menopause; menopause duration of <1 year (n = 57); premature menopause induced by surgery, chemotherapy, or radiation (n = 148); and hormone replacement therapy (HRT) for any cause (n = 185). In the end, 2,671 (83.0%) women were considered eligible for the analysis. The sample consisted of 1,893 premenopausal women and 778 postmenopausal women. Height was measured using a stadiometer in the upright position, and body weight was measured on a balanced scale (2,6). BMI was calculated using the following formula: BMI = body weight (kg)/height2(m). Waist circumference was measured at the midpoint between the bottom of the rib cage and the top of the lateral border of the iliac crest during minimal respiration. Blood pressure was measured using a mercury sphygmomanometer in the sitting position after a 10-min rest period. Two measurements were taken from all the subjects at 5-min intervals, and the average of the two measurements was used. Pulse pressure was defined as the difference between systolic and diastolic blood pressure. Blood samples were collected in the morning after an overnight fast, then centrifuged, refrigerated, and transferred to a national central laboratory in Seoul. Total cholesterol, triglycerides, HDL cholesterol, and plasma fasting glucose levels were measured using an autoanalyzer (Hitachi 747 autoanalyzer; Tokyo, Japan). LDL cholesterol level was calculated using the Friedewald equation if the triglyceride level was <400 mg/dl (8).
According to the National Cholesterol Education Program Adult Treatment Panel III (9), the metabolic syndrome is defined as the presence of three or more of the following risk factors: 1) abdominal obesity with a waist circumference
Self-reported questionnaires were administered to determine smoking status, alcohol intake, education level, household income, physical exercise level, and family history of medical disease. Smoking status was categorized into nonsmokers, current smokers, and ex-smokers. Alcohol consumption was categorized according to the amount and frequency of alcohol consumed: none, current drinker, risk drinker, and high-risk drinker (2). A risk drinker was a person who consumed
Statistical analysis
The prevalence of the metabolic syndrome and its risk factors increased with age in both Korean men and women (Fig. 1). Above the age of 50 years, the prevalence of the metabolic syndrome was significantly higher in women than in men (P < 0.05). Table 1 shows the baseline characteristics in relation to menopausal status. Postmenopausal women had significantly higher mean waist circumference, systolic blood pressure, pulse pressure, total cholesterol, LDL cholesterol, and triglyceride levels than premenopausal women, adjusted for age (P = 0.018, P = 0.001, P < 0.0001, P < 0.0001, P < 0.0001, and P = 0.006, respectively).
Table 2 displays the prevalence and ORs of the risk factors for the metabolic syndrome in relation to menopausal status. Abdominal obesity, elevated blood pressure, low HDL cholesterol, high triglycerides, and high fasting glucose were significantly associated with postmenopausal status (P < 0.0001 for all). However, when these factors were adjusted for age, only abdominal obesity was significantly associated with postmenopausal status (OR 1.61 [95% CI 1.152.25]; P = 0.005).
Table 3 presents the ORs for the metabolic syndrome after adjusting for menopausal status, BMI, smoking, alcohol consumption, education level, household income, exercise, residential area, and family history of CVD and diabetes. The unadjusted and multivariate-adjusted ORs for the metabolic syndrome in postmenopausal women were 7.50 and 1.60, respectively (95% CI 6.189.08 and 1.042.46, respectively) compared with premenopausal women. Multivariate analysis revealed that a high BMI and a family history of CVD and diabetes were significantly associated with an increased risk of the metabolic syndrome (OR 1.73 and 1.55, respectively). However, the multivariate model showed that smoking, alcohol intake, education level, household income, physical exercise level, and residential area were not significantly associated with the risk for the metabolic syndrome.
A higher prevalence of the metabolic syndrome among women aged >50 years compared with men of the same age has been reported in several Korean studies (6,1316) with various age-groups of peak prevalence. One Korean study reported an unusual peak prevalence in men of age 4049 years (13). This study was performed in a medium-sized city in Korea. The subjects were aged 40 years and were adjusted to the standard world population of Segi. To the best of our knowledge, our study is the first to demonstrate the effect of menopause on the metabolic syndrome in Korean women. This finding is consistent with a U.S. study (7) based on the National Health and Nutrition Examination Survey III. However, two small studies have reported no association between the risk of the metabolic syndrome and postmenopausal women. One study of 124 Argentine women reported that postmenopausal women had a 22% higher prevalence of the metabolic syndrome than premenopausal women, but this difference disappeared after an age adjustment (17). A study of 300 Swedish women reported that postmenopausal women not on HRT did not have an increased risk of the metabolic syndrome (18). These two studies appear to be less reliable due to their small sample size, which is in contrast to our study and the U.S. study (6).
Natural menopause is associated with increased central adiposity (19). Abdominal obesity is a cardiovascular risk factor that is independent of overall adiposity (20,21). Middle-aged women gain
The influence of menopause on blood pressure is difficult to evaluate because menopause coincides with aging (24). Some studies have reported a strong association between blood pressure and menopause, but other studies have not (2426). In Korea, middle-aged women ( Menopause is associated with an increase in total and LDL cholesterol and triglyceride levels (21,27), while HDL cholesterol level decreases with menopause (28,29). However, not all studies (28,30) agree with this conclusion. In our study, mean HDL cholesterol levels were similar in premenopausal and postmenopausal women. Oral postmenopausal hormone therapy decreases LDL cholesterol level and increases HDL cholesterol and triglyceride levels (31). A number of studies have shown that women on HRT have a reduced incidence of coronary heart disease and stroke. However, controversy still exists regarding the effect of HRT in preventing CVD in postmenopausal women (32). The Womens Health Initiative study group reported that the overall health benefits did not exceed the risks of using combined estrogen plus progestin in healthy postmenopausal women and conjugated equine estrogen in postmenopausal women (mean age was 63.2 years) who had undergone a hysterectomy (33,34). However, the recent Womens Health Initiative report suggests that conjugated equine estrogen in postmenopausal women aged 5059 years is associated with a lower risk of coronary heart disease (35). In our study, the small sample of women receiving HRT was excluded on account of its controversial effects. Further research will be needed to determine the effect of HRT on the metabolic syndrome in postmenopausal women. There were major limitations in our study. Selection bias might have occurred during the exclusion of ineligible women. In addition, our study was cross-sectional. This design limits generalization of our findings to all Korean women. In our study, modifiable health behaviors such as smoking and alcohol intake were not associated with an increased risk of the metabolic syndrome. A Korean study using the data from KNHANES 1998 found a significant association between alcohol and smoking and the risk of the metabolic syndrome in women (6). An association with smoking and alcohol intake might not have been observed due to the improper stratification, the limitations of a self-reported questionnaire, and other confounding factors. In conclusion, there is an association between postmenopausal status and an increased risk of the metabolic syndrome independent of normal aging in Korean women.
We thank the Korea Institute of Health and Social Affairs for providing us with the KNHANES 2001 data, as well as Hyejung Jung and Jungja Song (officers working at Gwangju City Hall) for their assistance.
A table elsewhere in this issue shows conventional and Système International (SI) units and conversion factors for many substances. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C Section 1734 solely to indicate this fact. Received for publication July 5, 2006. Accepted for publication December 9, 2006.
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