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

Abstract

OBJECTIVES: The ideal index for leanness and obesity in epidemiological studies should correlate strongly with body weight and with a direct measure of fat while minimizing the in¯uence of height. The preferred index is expected to show meaningful associations with subsequent mortality. Our aims were to compare weighta aheight, weighta aheight 2 (body mass index or BMI), and weighta aheight 3 as candidates for this index. DESIGN: We analysed cross-sectional data from surveys of 6948 adults (3334 men (mean age 43 y, mean BMI 24.8 kga am 2 ), and 3614 women (mean age 42 y, mean BMI 24.3 kga am 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 of obesity using Cox regression analysis for survival time from ®rst survey to death, or to follow up at the end of December 1995, after adjustment for age. Subjects dying within 5 y of the baseline survey were excluded from the analysis to avoid the bias of concurrent illness. We also studied subgroups including never smokers, subjects with no heart disease, and subjects`60 years of age at ®rst survey. RESULTS: In men, weighta aheight 2 met the criteria for a satisfactory index in that there was a very strong correlation with triceps skinfold, and a negligible correlation with height. For women, weighta aheight was as good a measure as weighta aheight 2 , with both having strong correlations with triceps skinfold, and minimal correlations with height. Weighta aheight 2 as a predictor of mortality in men of all ages showed the typical U-shaped associations that were similar and consistent and of variable statistical signi®cance. The signi®cances 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 smoking men P 0.007). In never smoking men there was a near linear positive relationship with all-cause mortality (P 0.018). In women weighta aheight 2 showed no consistent associations with mortality. There was a shallow Ushaped relationship with all-cause mortality (P 0.087), also seen in never smoking women (P 0.075). In assessing ideal' weight for height in this population, a weighta aheight 2 of 25 kga am 2 (range 22.5 ± 27.5 kga am 2 ) is appropriate. Weighta aheight and mortality showed very similar patterns in men to weighta aheight 2 with quite similar levels of statistical signi®cance. In women much more pronounced U-shaped curves were apparent in all groups and subgroups, with a signi®cant all-cause mortality trend for all women (P 0.029) and never smoking women (P 0.034). In assessing`ideal' weight for height a weighta aheight of 42.5 kga am (range 35 ± 50 kga am) appears appropriate for men and women. CONCLUSIONS: Weighta aheight 2 is an appropriate index of leanness and obesity in males at all ages, whereas weighta aheight is at least as good an index for females. In mortality studies weighta aheight 2 and weighta ahei...

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