Objective: To examine the effect of age on the relationship between body mass index (BMI) and waist circumference (WC), and the usefulness of BMI, WC and waist-hip ratio (WHR) in predicting mortality and cardiovascular risk in the elderly population.
Design: Longitudinal observational study of 36 months duration.
Subjects and method: A stratified random sample of 2,032 Chinese subjects (990 male, 1,033 female) mean age (s.d.) 80.1 (7.5), interviewed and examined at baseline and after 36 months. Deaths and presence of diabetes mellitus and hypertension were documented. A younger data set of 1,010 subjects (500 male, 510 female), mean age (s.d.) 45.5 (11.6), was used for comparison of the BMI-WC relationship between younger and older subjects. In predicting outcomes using different values of BMI, WC and WHR, receiver operating characteristic curve analysis was used to derive cut-off values with optimal sensitivity and specificity, and the likelihood ratios for mortality, diabetes and hypertension for different anthropometric values were plotted.
Results: The waist circumference values corresponding to BMI values of 25 and 30 kg/m(2) were higher in elderly (92 and 103 cm for men; 88 and 99 cm for women) compared with younger subjects (85 and 97 cm for men; 78 and 88 cm for women). BMI and WC are inversely associated with mortality, in both men and women, positively associated with diabetes in men but not in women. WC was positively associated with hypertension in men and women. WHR was not associated with any outcome measures. The anthropometric measurement at the point of intersection of the likelihood curves for mortality and diabetes may be considered the optimum value, being BMI=21 kg/m(2) for men and 25 kg/m(2) for women, WC between 80 and 85 cm, and WHR 0.88-0.90.
Conclusion: Waist measurement values for predicting health outcomes in elderly people aged 70 y and over are different compared with younger subjects, and have similar predictive accuracy compared with body mass index. Waist-hip ratio is not a useful predictor.