Body mass index and alternative indices of obesity in relation to height, triceps skinfold and subsequent mortality: the Busselton Health Study

OBJECTIVES: The ideal index for leanness and obesity in epidemiological stu dies should correlate strongly with body weight and with a direct measure o f Pal while minimizing the influence of height. The preferred index is expe cted to show meaningful associations with subsequent mortality. Our aims we re to compare weight/height, weight/height(2) (body mass index or BMI), and weight/height(2) as candidates for this index. DESIGN: We analysed cross-sectional date from surveys of 6948 adults (3334 men (mean age 43y, mean BMI 24.8 kg/m(2)), and 3614 women (mean age 42y, me an BMI 24.3 kg/m(2))) in Busselton, Australia whose weight, height, triceps skinfold, and cardiovascular risk factors were measured from 1966 through to 1978. In these same subjects we studied the mortality risks of indices o f obesity using Cox regression analysis for survival time from first survey to death, or to follow up at the end of December 1995, after adjustment fo r age. Subjects dying within 5 y of the baseline survey were excluded from the analysis tea avoid the bias of concurrent illness. We also studied subg roups including never smokers, subjects with no heart: disease, and subject s <60 years of age at first survey. RESULTS: In men, weight/height(2) met the criteria for a satisfactory index in that there was a very strong correlation with triceps sltinfold, and a negligible correlation with height. For women, weight/height was as good a measure as weight/height(2), with bath having strong correlations with tric eps skinfold, and minimal correlations with height. Weight/height(2) as a p redictor of mortality in men of all ages showed the typical U-shaped associ ations that were similar and consistent and of variable statistical signifi cance. The significances of the hazard ratio curves were the strongest for cardiovascular disease deaths (all men P=0.001; men without heart: disease at baseline P<0.001; never smelting men P=0.007). In never smelting men the re was a near linear positive relationship with all-cause mortality (P=0.01 8). In women weight/height(2) showed mo consistent associations with mortal ity. There was a shallow U-shaped relationship with all-cause mortality (P= 0.087), also seen in never smoking women (P=0.075). In assessing 'ideal' we ight for height in this population, a weight/height(2) of 25kg/m(2) (range 22.5-27.5kg/m(2)) is appropriate. Weight/height and mortality showed very s imilar patterns in men to weight/height(2) with quite similar levels of sta tistical significance. In women much more pronounced U-shaped curves were a pparent in all groups and subgroups, with a significant all-cause mortality trend for all women (P=0.029) and never smoking women (P=0.034). In assess ing 'ideal' weight for height a weight/height of 42.5 kg/m (range 35-50 kg/ m) appears appropriate for men and women. CONCLUSIONS: Weight/height(2) is an appropriate index of leanness and obesi ty in males at all ages, whereas weight/height is at least as good an index for females. In mortality studies weight/height(2) and weight/height predi ct mortality similarly in males, brat weight/height is a better discriminat ion of mortality in females.