Relative sitting height and the interpretation of the body mass index.

The body mass index (BMI) is being used widely as an index of overweight and undernutrition. The effects of variations of shape as evinced by relative sitting height (sitting height/stature, SH/S) on BMI were determined using mean data from 95 samples of men and 63 samples of women of non-European origin, representing 18,000 individuals. The linear regression coefficients of BMI on SH/S (b +/- standard error) were 0.78 +/- 0.16 (t = 4.8) in men and 1.19 +/- 0.22 (t = 5.3) in women. Correlations coefficients were 0.45 and 0.56, respectively. These regression coefficients compare with a predicted change of 0.9 kg/m2 per 0.01 difference in SH/S using a modelling approach. The wide variation within and between populations precludes a simple adjustment for SH/S, and in the interpretation of BMI additional anthropometric measurements may be necessary.