The Relationship Between Waist Circumference and the Risk of Stroke and Myocardial Infarction in a Japanese Urban Cohort
The Suita Study
Background and Purpose— Body mass index is most commonly used as the obesity index. Recently, waist circumference (WC) has been shown to be associated with the risk of cardiovascular disease (CVD). However, no studies have observed an association between WC and CVD in Japan. We examined the relationships of WC and body mass index with CVD in a Japanese urban population.
Methods— We studied 5474 Japanese individuals (aged 30 to 79 years without CVD at baseline) who completed a baseline survey and received follow-up through December 2005. WC was measured at the umbilical level of participants in the standing position to the nearest 1 cm. The Cox proportional hazard ratios for CVD according to the quartiles of WC were calculated after adjustment for age, smoking, and drinking status.
Results— During a mean follow-up of 11.7 years, 207 strokes and 133 myocardial infarctions were documented. In women, compared with the lowest quartile (WC <70 cm), the hazard ratio (95% CIs) after adjusting for age, smoking, and drinking in the highest quartile (WC ≥84 cm) were 1.85 (1.03 to 3.31) for CVD and 2.64 (1.16 to 6.03) for stroke. However, no such relationships of WC with CVD or stroke risk were observed in men. After further adjustment of hypertension, diabetes, and hypercholesterolemia, all of the mentioned relationships were not statistically significant. No associations of body mass index with CVD or strokes were observed.
Conclusions— WC may be a better predictor for CVD or stroke in Japanese women.
The increasing prevalence of obesity worldwide has led to concern about the impact of obesity on the risk of cardiovascular disease (CVD).1 Body mass index is most commonly used as the measurement of obesity. Recently, abdominal obesity measured by waist circumference (WC) has been shown to be associated with the risk of CVD.2,3 However, no cohort study on the relationship between WC and the risk of CVD has been performed in Japan. We therefore examined the relationship of WC and body mass index with the incidence of CVD and stroke in a Japanese urban population.
The Suita Study starting from September 1989, a random sampling of Japanese urban residents, has been described previously (response rate: 53%).4–6 Participants (n=5474) who attended the baseline examination without a history of CVD were followed up. The details of the methods and confirmation of stroke and myocardial infarction in the Suita Study have been described elsewhere.4–6 The follow-up was continued until one of the following end points, whichever came first: date of the first myocardial infarction or stroke event, date of death, date of leaving Suita, or December 31, 2005. This study was approved by the Institutional Review Board of the National Cardiovascular Center.
Analyses of variance and χ2 tests were used to compare mean values and frequencies. The Cox proportional hazard ratios and 95% CIs for CVD were calculated according to the quartiles of WC after adjusting for age, smoking, and drinking status. All statistical analyses were performed with SPSS (Version 13.0J; SPSS Japan Inc, Tokyo, Japan).
During a mean follow-up of 11.7 years, we documented 207 strokes and 133 myocardial infarctions. As shown in Table 1, both men and women with higher WC were older; had a higher prevalence of hypertension, diabetes, and hypercholesterolemia; and had a lower prevalence of current smokers. The correlations between body mass index and WC were 0.84 in men and 0.75 in women.
The highest quartile of WC was associated with a significant increase in the risk of CVD and stroke compared with the lowest quartile in women but not in men (Table 2). Moreover, in women, the association between WC and CVD disappeared after further adjustment for hypertension, diabetes, and hypercholesterolemia. These associations were not also statistically significant even after removing subjects with any of mentioned 3 risk factors (data not shown). When we sequentially changed the cutoff values of WC, an increased risk of CVD was observed in women with WC ≥80 cm (Figure). No associations of body mass index with CVD or strokes were observed (data not shown).
In this cohort study, abdominal obesity (WC ≥80 cm) was positively associated with CVD in women, which is the first study of the relationships in Japan. In the 2 large cohort studies in the Western population,2,3 WC was positively associated with the risk of CVD. However, the current study only observed the positive relationships of WC with CVD and stroke in women. The reasons for the sex difference are unclear but may involve differences in race, lifestyle background, severity of obesity, or prevalence of risk factors in nonobese subjects.
Abdominal obesity, strongly correlated with WC, has been associated with insulin resistance,7 diabetes,8 lipid abnormalities,9 and blood pressure elevation.10 The association between WC and CVD disappeared after further adjustment for cardiovascular risk factors or removing subjects with diabetes, hypertension, or hypercholesterolemia. Therefore, WC might be likely on the causal pathway leading to the more proximal risk factors for CVD and contributes to risk through those factors. Abdominal obesity without other cardiovascular risk factors does not predict the risk of CVD. However, it should be careful that increasing abdominal obesity might lead to those factors.
Our study has the following limitations: regression dilution bias, small sample size for subgroup analysis, lifestyle background, and measurement of WC at the umbilical level rather than at the midpoint between the lower rib and the iliac crest. However, the correlation coefficients between values measured by using the both methods for measurement of WC were reported to be high.11
In conclusion, our findings suggested that WC was associated with an increased risk of CVD and stroke in Japanese women. From a public health perspective, measurement of WC could be a useful tool for use in preliminary screening for high risk of CVD.
We express our deepest gratitude to all members of the Suita Medical Association and Suita City Health Center. We thank Dr Yasushi Kotani, the president of the Suita Medical Association, and Dr Hitonobu Tomoike, Director-General of the Hospital, National Cardiovascular Center, for their support of the Suita Study. We also thank all of the researchers and staff of the Department of Preventive Cardiology for performing medical examinations and follow-up. We also thank Satsuki-Junyukai and the volunteers involved in the administration of the Suita Study.
Sources of Funding
This study was supported by a Grant-in-Aid from the Ministry of Health, Labor, and Welfare of Japan (H20-SeiShu-013 and H19-SeiShu-017); a Research Grant for Cardiovascular Disease from the Ministry of Health, Labor, and Welfare (19S-6, 21S-1); the Mitsui Life Social Welfare Foundation; and the Chiyoda-kenko Foundation.
Continuing medical education (CME) credit is available for this article. Go to http://cme.ahajournals.org to take the quiz.
This article encompasses the doctoral dissertation of Y.F.
- Received September 28, 2009.
- Revision received November 9, 2009.
- Accepted November 20, 2009.
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