Waist-to-hip ratio is a better anthropometric index than body mass index for predicting the risk of type 2 diabetes in Taiwanese population
Introduction
Body mass index (BMI), a general measure of obesity, has been reported to be closely related to the risk of type 2 diabetes and hypertension [1], [2], [3]. Because diabetic and hypertensive risks are related to intra-abdominal fat rather than subcutaneous fat [4], [5], waist circumference (WC) or waist-to-hip ratio (WHR) can better reflect the accumulation of intra-abdominal fat compared with BMI, which is affected by the height index. WC or WHR has been shown to be a better predictor of the risk of type 2 diabetes and hypertension than BMI [6], [7], [8], [9]. However, age [10], [11], [12], sex [13], and ethnicity [14], [15], [16] can confound the predictive accuracy of WC or WHR.
Adipose tissue distribution is affected by age. The consequence of abdominal obesity might be insulin resistance, which can lead to impaired glucose tolerance and progression to type 2 diabetes [10], [17], [18]. Age has been shown to be a confounder in the BMI-specific associations between WHR and glycemic status [10]. Because diabetic and hypertensive risks are related to visceral fat mass, anthropometric indices might not be good predictors of risk in young or older subjects [10], [12], [19]. Sex difference is also a confounder in the predictive risks of diabetes and hypertension. Sex hormone concentration has an influence on body fat accumulation and the development of insulin resistance [20], [21]. Abdominal fat might be more important than the total body fat in predicting the risk of type 2 diabetes in women [13]. In addition to BMI, WC, and WHR, waist-to-height ratio (WHtR) was shown to be an independent variable in predicting risk of developing hypertension and abnormal glucose tolerance in both sexes [22], [23], [24]. The WHtR, an indicator of both abdominal fat and body weight, might be another simple index that can be used to predict the risk of type 2 diabetes and hypertension. Ethnicity is another confounder in the predictive risk of type 2 diabetes and hypertension [14]. Asians generally have smaller frames and lower body fat distribution than whites, even when they have similar BMI [25], [26]. However, Asian Indians have more abdominal fat than whites [27]. A prevalent difference in the association between BMI and hypertension was observed in 3 different ethnic groups including Chinese, Filipinos, and whites [14]. Different cutoff values for anthropometric indices seem to be required to correlate the risk of type 2 diabetes and hypertension in different ethnic groups.
Since 2002, type 2 diabetes has been the 4th and hypertension the 10th leading causes of death in Taiwan [28]; it is important to identify a convenient, sensitive screening index for predicting the risk of type 2 diabetes and hypertension in the general Taiwanese population. However, the evidence demonstrating the correlation of BMI, WC, WHR, WHtR, or WC/BMI ratio with the risk of type 2 diabetes and hypertension in the Taiwanese population is scant and inconsistent. We hypothesized that other anthropometric index rather than BMI could more accurately predict the risk of type 2 diabetes and hypertension. Therefore, the purpose of this study was to ascertain which anthropometric index can be better at predicting the risk of type 2 diabetes and hypertension in the Taiwanese population. Because receiver operating characteristic (ROC) plots can provide an index of a precise and valid measure of diagnostic accuracy [29], ROC analysis was then used to detect which level of anthropometric indices mark thresholds for type 2 diabetes and hypertension.
Section snippets
Subjects and design
The study data were obtained from the Nutrition and Health Survey in Taiwan (1993-1996), a national survey that was conducted to examine the changes in nutrition and health status of Taiwanese individuals. This survey was conducted by the Bureau of Health Promotion of the Department of Health in Taiwan. A stratified, multistage clustered sampling scheme was performed [30], [31], and the detailed procedure has been described elsewhere [30]. Briefly, data were drawn from 7 geographical districts
Results
In total, 2545 men and 2562 women were included in this study. Subjects' ages ranged from 18 to 96 years, with mean and median ages of 47.7 and 48.0 years, respectively. There were 260 subjects (111 men, 149 women) with type 2 diabetes mellitus and 748 subjects (327 men, 421 women) with hypertension. The prevalence rates of type 2 diabetes and hypertension were 5.1% and 14.6% for the total population, respectively; women had a higher prevalence of type 2 diabetes (5.8% vs 4.4%) and hypertension
Discussion
Several studies have indicated that age is a confounder when using anthropometric indices to predict the risk of type 2 diabetes or hypertension [10], [12], [19]. Daniel et al [10] stratified subjects into 3 age categories: 18-34 (n = 53), 35-49 (n = 62), and at least 50 years (n = 36), showing that age confounded the association between WHR and glycemic status. We also stratified our subjects according to age but used different categories than the one used by Daniel et al: 18-44 (n = 2266),
Acknowledgment
Preparation of this article was supported by a grant from the National Science Council, Taiwan (NSC 94-2320-B-040-037). Data analyzed in this study were collected by the research project “Nutrition and Health Survey in Taiwan (NAHSIT)” supported by the Department of Health in Taiwan (DOHFN8202, DOH-83-FS-41, DOH-84-FS-11, DOH-85-FS-11, DOH-86-FS-11). This research project was carried out by the Institute of Biomedical Sciences of Academia Sinica and by the Department of Biochemistry, College of
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