Relationships Between Indices of Obesity and Its Cardiovascular Comorbidities in a Chinese Population

Transcription

1 Circ J 2008; 72: Relationships Between Indices of Obesity and Its Cardiovascular Comorbidities in a Chinese Population Rui Li, MD ; Wei Lu, MD, PhD ; Jian Jia, MD, MPH*; Shengnian Zhang, MD; Liang Shi, MD; Yanyun Li, MD; Qundi Yang, MD; Haidong Kan, MD, PhD**, Background Current definitions of overweight/obesity and central adiposity guidelines are based on Western populations, and may not be appropriate for the Chinese population. More data among Chinese are needed to address this issue. We aimed to identify cut-offs for body mass index (BMI) and waist circumference that confer increased risk of cardiovascular disease in a Chinese population in Shanghai. Methods and Results A representative, cross-sectional sample of 13,817 adults aged >18 years was studied in Shanghai. In men and women, blood pressure (systolic and diastolic), total cholesterol, low-density lipoproteincholesterol, triacylglycerol, and glucose values were incrementally higher and mean high-density lipoprotein-cholesterol values were incrementally lower with increased BMI and waist circumference. Both the point at which sensitivity equaled specificity and the shortest distance in the receiver operating characteristic s for hypertension, dyslipidemia, diabetes, or 2 of these risk factors generally suggested a BMI cut-off value of 24kg/m 2 for both men and women, and a waist circumference cut-off value of 85 cm for men and 80 cm for women. Conclusions A BMI cut-off of 24kg/m 2 for both men and women, and a waist circumference cut-off of 85cm for men and 80cm for women might be appropriate for use in identifying adults at high risk of developing cardiovascular disease and serve as public health action thresholds in Shanghai residents. (Circ J 2008; 72: ) Key Words: Body mass index; Cardiovascular disease; Obesity; Waist circumference The prevalence of obesity and overweight has increased dramatically in both economically developed countries and developing countries. 1 It is estimated that more than 1 billion adults worldwide are overweight (ie, body mass index (BMI) of kg/m 2 ) and more than 300 million adults worldwide are obese (BMI 3 kg/m 2 ). 2 Body composition and body fat distribution are 2 important determinants for the risk of cardiovascular disease. Observational epidemiological studies have documented that obesity is associated with cardiovascular risk factors such as diabetes mellitus, hypertension and dyslipidemia. 3 5 The current definitions of overweight/obesity and central adiposity recommended by the World Health Organization (WHO) are based on data from Western populations. 2 However, some recent data suggest that these definitions may not be appropriate for the Chinese population, which have a higher percentage of body fat than Whites at any given BMI. 6 In China, the prevalence of overweight is much lower than (Received November 19, 2007; revised manuscript received December 17, 2007; accepted December 27, 2007) Shanghai Municipal Center for Disease Control and Prevention, *Zhabei Administration Centre for Community Health and Service and **Department of Environmental Health, School of Public Health, Fudan University, Shanghai, China The three authors contributed equally. Mailing address: Wei Lu, MD, PhD, 1380 Zhong-Shan-Xi Road, Shanghai , China. weiloo@scdc.sh.cn or Haidong Kan, MD, PhD, Box 249, 138 Yi-Xue-Yuan Road, Shanghai , China. haidongkan@gmail.com All rights are reserved to the Japanese Circulation Society. For permissions, please cj@j-circ.or.jp the Western population; 7 however, obesity comorbidities in the Chinese population have rates much closer to those of Western populations. For example, the prevalence of diabetes has increased to 5.2% in Chinese adults, which is comparable to the rate of 7.8% in Americans. 8 In addition, Chinese adults have a stronger association between BMI and obesity-related disease conditions compared with the US population; 9 a moderate increase in BMI makes a Chinese adult more prone to hypertension, dylispidemia and hyperuricemia. 10 In response to these findings, overweight in the Chinese population is suggested to be defined as a BMI 24 kg/m 2, and waist circumference cut-off values are suggested to be 80cm for both men and women. 6 However, these recommendations are provisional and require further validation with more epidemiologic study. 11 In the current analysis, our aim was to identify the cut-off values for BMI and waist circumference that are associated with increased risk of cardiovascular disease in a Chinese population in Shanghai, China. Methods Study Participants The study participants were those who had participated in the Shanghai Type 2 Diabetes Survey. 12 Briefly, the Survey used a stratified sampling method to select a representative sample of the general population aged >15 years in Shanghai, China. A total of 14,351 individuals were randomly selected from 12 primary sampling units (street districts in urban areas or townships in rural areas) and invited to participate. We excluded 534 subjects aged between 15 and 18 years because the standard definitions of cardiovascular comor-

2 974 LI R et al. Table 1 Cardiovascular Risk Factors in Shanghai Residents by BMI Category BMI <21 21 BMI < BMI < BMI < BMI <29 BMI 29 Population distribution (%) SBP (mmhg) 117.5± ± ± ± ± ±0.9 DBP (mmhg) 74.8± ± ± ± ± ±0.5 Total cholesterol (mg/dl) 167.1± ± ± ± ± ±1.9 HDL-cholesterol (mg/dl) 56.0± ± ±0.4 5± ± ±0.8 LDL-cholesterol (mg/dl) 90.8± ± ± ± ± ±1.7 Triacylglycerol (mg/dl) 105.3± ± ± ± ± ±5.8 Glucose (mg/dl) 87.2± ± ± ± ± ±1.5 Population distribution (%) SBP (mmhg) 112.6± ± ± ± ± ±0.7 DBP (mmhg) 71.6± ± ± ± ± ±0.4 Total cholesterol (mg/dl) 173.1± ± ± ± ± ±1.6 HDL-cholesterol (mg/dl) 61.8± ± ± ± ± ±0.7 LDL-cholesterol (mg/dl) 92.3± ± ± ± ± ±1.4 Triacylglycerol (mg/dl) 97.0± ± ± ± ± ±3.8 Glucose (mg/dl) 87.1± ± ± ± ± ±1.1 BMI, body mass index; SBP, systolic blood pressure; DBP, diastolic blood pressure; HDL, high-density lipoprotein; LDL, low-density lipoprotein < BMI (kg/m 2 ) < BMI (kg/m 2 ) Fig 1. Frequency of one or more risk factors (ie, hypertension, dyslipidemia, and diabetes) by body mass index (BMI) category in men and women. bidities (eg, hypertension) are established for adults >18 years. The final analysis included 13,817 subjects. The Institutional Review Board at Shanghai Municipal Center of Disease Control and Prevention approved the study. Informed consent was obtained from each participant before data collection. Anthropometric Measurements Data on demographic, socioeconomic, medical history, and other health-related variables were collected with a standard questionnaire validated in Chinese. Trained technicians performed the interview in community clinics in the participants residential areas. Anthropometric measures were taken according to a standard protocol. Body weight and height were recorded

3 Obesity and Cardiovascular Comorbidities 975 Table 2 Sens, Spec and in the ROC Curves for BMI Cut-Offs Hypertension Dyslipidemia Diabetes 2 Risk factors BMI cut-off Percentile (kg/m 2 ) in ROC in ROC in ROC in ROC Sens, sensitivity; Spec, specificity; ROC, receiver operating characteristic. Other abbreviation see in Table 1. while the subject was in light clothing and without shoes. Waist circumference was measured with a standard tape measure on bare skin, 1 cm above the naval. The BMI was calculated as weight (kg) divided by height (m 2 ). Laboratory Methods and Blood Pressure Measurement After the participants had fasted overnight, blood samples were drawn to measure serum total cholesterol, highdensity lipoprotein (HDL)-cholesterol, triacylglycerols, and glucose. Blood specimens were obtained at least 1 h after the participant s arrival at the field center, and were processed and stored at 70 C. Total cholesterol, HDL-cholesterol, and triacylglycerols were measured enzymatically using commercial reagents. Low-density lipoprotein (LDL)-cholesterol concentrations were calculated using the Friedewald equation for those participants who had a triacylglycerol concentration of <400 mg/dl: LDL-cholesterol = Total cholesterol HDL-cholesterol triacylglycerols/5. Dyslipidemia was defined as having either total cholesterol 200 mg/dl, LDL-cholesterol 130 mg/dl, or HDL-cholesterol <35mg/dl. 6 Diabetes was defined as having fasting plasma glucose 126 mg/dl, use of insulin or oral hypoglycemic agents, or a self-reported history of diabetes. Three blood pressure measurements were obtained by trained nurses and physicians according to a standard protocol; the measurements were made with the participant in a sitting position after 5 min of rest. The participants were advised to refrain from coffee, tea, or alcohol intake; cigarette smoking; and vigorous exercise for 30min before their examination. Hypertension was defined as self-reported use of antihypertensive medication within the past 2 weeks, or an average systolic blood pressure 140 mmhg, an average diastolic blood pressure 90 mmhg, or both. Statistical Analysis By creating dichotomous variables for each BMI and waist circumference value, we calculated the sensitivity and specificity of each BMI and waist circumference level for the detection of hypertension, dyslipidemia, diabetes, and 2 or more of these risk factors. The distance on the receiver operating characteristic (ROC) of each BMI and waist circumference value was calculated as [(1 sensitivity) 2 +(1 specificity) 2 ]. The BMI or waist circumference values with the shortest distance on the ROC were considered in the determination of appropriate cut-off values. All data analyses were conducted by using SAS (ver. 9.12; Cary, NC, USA). Results BMI For men and women, mean blood pressure (systolic and diastolic), total cholesterol, LDL-cholesterol, triacylglycerol, and glucose values were higher, but mean HDL-cholesterol values were lower, with higher BMI, in a linear fashion (Table 1). The proportion of individuals having hypertension, dyslipidemia, diabetes, or a combination of the 3, by BMI category for both men and women, is shown in Fig 1. The frequency of having at least 1 risk factor doubled from a BMI of <21kg/m 2 to a BMI of 29kg/m 2, largely because of those participants with 2 risk factors. The population percentile of each BMI level and the sensitivity, specificity, and distance on the ROC for the detection of hypertension, dyslipidemia, diabetes, and 2 of these risk factors are presented in Table 2 for men and women separately. The specificity, sensitivity, and distances on the ROC s were generally similar for cardiovascular disease risk factors among both men and women. For men, the BMI point at which sensitivity equaled specificity was between 24 and 25 kg/m 2 for all risk factors; and the shortest distances on the ROC was at a BMI of 24kg/m 2 for hypertension, dyslipidemia and diabetes diabetes, and a BMI of 25kg/m 2 for 2 risk factors. For women,

4 976 LI R et al. Table 3 Cardiovascular Risk Factors in Shanghai Residents by Waist Circumference Category Waist circumference (cm) < Population distribution (%) SBP (mmhg) 117.7± ± ± ± ± ±0.7 DBP (mmhg) 75.1± ± ± ± ± ±0.4 Total cholesterol (mg/dl) 163.9± ± ± ± ± ±1.5 HDL-cholesterol (mg/dl) 55.8± ± ± ± ± ±0.6 LDL-cholesterol (mg/dl) 88.5± ± ± ± ± ±1.4 Triacylglycerol (mg/dl) 102.2± ± ± ± ± ±4.7 Glucose (mg/dl) 85.8± ± ± ± ± ±1.2 Population distribution (%) SBP (mmhg) 114.6± ± ± ± ± ±1.0 DBP (mmhg) 73.1± ± ± ± ± ±0.5 Total cholesterol (mg/dl) 173.7± ± ± ± ± ±2.1 HDL-cholesterol (mg/dl) 6± ± ± ± ± ±1.0 LDL-cholesterol (mg/dl) 94.2± ± ± ± ± ±1.9 Triacylglycerol (mg/dl) 99.5± ± ± ± ± ±5.0 Glucose (mg/dl) 87.7± ± ± ± ± ±1.4 Abbreviations see in Table < Waist circumference (cm) < Waist circumference (cm) Fig 2. Frequency of one or more risk factors (ie, hypertension, dyslipidemia, and diabetes) by waist circumference category in men and women. the BMI point at which sensitivity equaled specificity was between 23 and 24kg/m 2 for dyslipidemia, and between 24 and 25kg/m 2 for hypertension, diabetes and 2 risk factors; the shortest distances on the ROC was at a BMI of 24 kg/m 2 for hypertension, dyslipidemia and 2 risk factors, and a BMI of 25 kg/m 2 for diabetes. Waist Circumference For men and women, mean systolic blood pressure, diastolic blood pressure, total cholesterol, LDL-cholesterol, and triacylglycerol values were higher, but HDL-cholesterol values were lower, with higher waist circumference, in a linear fashion (Table 3). The proportion of individuals

5 Obesity and Cardiovascular Comorbidities 977 Table 4 Sens, Spec and in the ROC Curves for Waist Circumference Cut-Offs Hypertension Dyslipidemia Diabetes 2 Risk factors Waist cut-off Percentile (kg/m 2 ) in ROC in ROC in ROC in ROC Abbreviations see in Table 2. having hypertension, dyslipidemia, diabetes, or a combination of the 3, by waist circumference categories for both men and women, is shown in Fig2. The frequency of having at least 1 risk factor doubled from a waist circumference of <75 cm to a waist circumference of 95 cm, largely because of those participants with 2 risk factors. The population percentile of each waist circumference level, as well as the sensitivity, specificity, and distance on the ROC for the detection of hypertension, dyslipidemia, diabetes, and 2 of these risk factors, are presented in Table 4 for men and women separately. The specificity, sensitivity, and distances on the ROC s were generally similar for cardiovascular disease risk factors among both men and women. For men, the waist circumference point at which sensitivity equaled specificity was between 80 and 85 cm for hypertension and dyslipidemia, and between 85 and 90 cm for diabetes and 2 risk factors; and the shortest distances on the ROC was at a waist circumference of 85 cm for all risk factors. For women, the waist circumference point at which sensitivity equaled specificity was between 75 and 80 cm for hypertension, dyslipidemia and 2 risk factors, and between 80 and 85cm for diabetes; and the shortest distances on the ROC was at a waist circumference of 75cm for dyslipidemia, and 80cm for hypertension, diabetes and 2 risk factors. Discussion Data from the present study show a continuous increase in cardiovascular disease risk factor levels and prevalence of hypertension, diabetes, and dyslipidemia with higher BMI and waist circumference values among this particular Chinese population in Shanghai. These findings agree with other studies of Chinese and other Asian populations, documenting linear relations of BMI or waist circumference with cardiovascular disease risk factors. 5,6,10,13 16 Moreover, based on the sensitivity, specificity and ROC calculations, our data suggest a BMI of 24kg/m 2 for both men and women, and a waist circumference of 85 cm for men and 80 cm for women as appropriate cut-off values for the designation of overweight and central adiposity in this population. Compared with Western populations, we found that lower cut-off values for BMI and waist circumference indicate a high risk for cardiovascular disease. Previous studies show that Asian populations have a higher percentage of body fat than do Western populations for a given BMI or waist circumference For example, in Shanghai Chinese migrating to the US, Wang and colleagues reported a lower BMI but a higher percentage of body fat than White people of the same age and gender. 20 Also, Deurenberg et al reported that Chinese have 1.9 BMI units lower than Caucasians at the same percentage of body fat. 17 At the same level of total fatness, the Asian population is associated with higher visceral adiposity than Caucasians. 21 The slender body build with less muscle and relatively short leg length in some Asian populations might be possible reasons for explaining these differences. 22 In addition, a combination of malnutrition during childhood with overnutrition during adulthood, which is typical of developing countries that are in nutritional transition, may significantly increase the risk for obesity and cardiovascular diseases in adult life. 23,24 All these differences might partially account for the greater prevalence of obesity-related risk factors at low BMI values and a stronger association between BMI and cardiovascular disease in some Asian populations. These studies strongly support the need for Chinese-specific cut-off values for BMI and waist circumference. The selection of cut-off points for continuous variables usually involves compromise between sensitivity and specificity. The cut-off values recommended here in this study s Chinese population in Shanghai were identified as the values of BMI and waist circumference that balanced sensitivity and specificity. However, given the continuous increase in the prevalence of cardiovascular disease risk factors with increasing BMI and waist circumference shown by the present data, we have to acknowledge that all cut-off values are arbitrary; no threshold for BMI or waist circumference can be determined whereby values below the threshold confer no increased risk of cardiovascular disease and values above confer a uniform increased risk.

6 978 LI R et al. Study Limitations The present study has various strengths and limitations. This was a representative sample of the average Shanghai residential population. Thus, these results can be generalized to the entire adult population of Shanghai aged >18 years. Additionally, we provided data for a wide range of BMI and waist circumference values, stratified by gender, to enable local public health officials to use these data for the development of BMI and waist circumference definitions based on decision rules that may differ from those we applied. These data are cross-sectional, however. Future prospective studies in a representative sample of the adult Chinese population are needed. Because BMI and waist circumference are supposed surrogates for body fatness and fat distribution, the present study did not have direct measures of body fatness or fat distribution. Also, other obesity comorbidities, such as cancer, cholelithiasis, and mortality may have a different relationship with BMI and waist circumference. 25 Moreover, in our analysis, a definition of diabetes mellitus included a self-reported history of diabetes; this might obscure the relationship between indices of obesity and diabetes mellitus. Conclusion In summary, the data of the present study suggest that a BMI value of 24 kg/m 2 for both men and women, and a waist circumference value of 85 cm for men and 80 cm for women, as appropriate for use in identifying those who are at high risk for cardiovascular disease in the Chinese population in Shanghai, and who require further screening and intervention. Acknowledgment This study was supported by the Key Program of Shanghai Municipal Committee of Science and Techonology (04 DZ19502). References 1. WHO Expert Consultation. Appropriate body mass index for Asian populations and its implications for policy and intervention strategies. 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