Correlation between waist circumference and metabolic risk among population with normal body mass index

Objective To investigate whether waist circumference is associated with metabolic risk among people with normal body mass index (BMI). Moreover, cut-off values of waist circumference were analyzed with respect to risks for metabolic disorders to provide a guidance for early detection and prevention of metabolic disorders in population with normal BMI. Methods The population-based cohort study was based on China National Diabetes and Metabolic Disorders Survey in 2007-2008. We calculated optimal cut-offs of waist circumference by computing the risk associated with type 2 diabetes mellitus (T2DM), metabolic syndrome (MS) and hypertension with receiver operating characteristic (ROC) curve analysis. Furthermore we weighed the prevalence rates of metabolic diseases to obtained the most optimal cut-offs. Results A total of 22 053 participants were included in this study who have normal BMI (18.5 kg/m2≤BMI<24 kg/m2) with the average of (43±14) years old. The average age of 7 988 male and 14 065 female were respectively (44±15) and (42±13) years old. With the increase in waist circumference, of the risks for type 2 diabetes, MS and other metabolic disorders showed an upward trend in the population with normal BMI regardless of gender. The relationship between waist circumference and prevalence was analyzed for T2DM, MS and hypertension. For male, the optimal cut-offs of waist circumference were 78, 79 and 77 cm for T2DM, MS and hypertension, respectively, female were 73, 78 and 73 cm. Weighed cut-off for male was 78 cm and 74 cm for female after further analysis. Taking into consideration of menopause at the age of 49 for female, we found that the waist circumference was 74 cm (not menopause) and 77 cm (menopause). The prevalence rates of T2DM, MS and hypertension were 11.5% (465/4 111), 12.8% (528/4 111) and 25.0% (1 029/4 111) for male and 9.6% (632/6 553), 12.1% (795/6 553), 22.3% (1 463/6 553) for female respectively by our cut-offs. The same method was used to determine the optimal cut-offs of the waist circumference in all age groups. In 20-30, 31-40, 41-50, 51-60, 61-70 and ≥71 years old groups, the male's cut-offs were 76, 81, 79, 76, 76 and 81 cm, respectively; 74, 74, 73, 76, 81 and 76 cm for female. Conclusion It is suggested that metabolic disorders should be screened for people with normal BMI but having waist circumference≥78 cm in male and ≥74 cm in female. Key words: Diabetes mellitus, type 2; Hypertension; Body mass index; Waist circumference; Metabolic syndrome