RELATIONSHIP BETWEEN BLOOD-PRESSURE AND BODY-MASS INDEX IN LEAN POPULATIONS

Associations between body mass index (BMI) and blood pressure (BP) hav e been consistently observed, but remain poorly understood. One unreso lved question is whether there is a linear relationship across the ent ire BMI range. We investigated this question among 11 235 adult men an d women from seven low-BMI populations in Africa and the Caribbean. We used kernel smoothing and multivariate linear and spline regression m odeling to examine gender differences in the relationship and to test for a threshold. Age-adjusted slopes of BP on BMI were uniformly highe r in men than women, with pooled slope ratios of 2.00 and 2.20 for sys tolic and diastolic BPs, respectively. Men displayed no evidence of ag e modification or nonlinearity in the relationship, and the age-adjust ed slope of systolic BP on BMI was 0.90 (95% confidence interval [CI], 0.76 to 1.04). Women demonstrated both age modification and nonlinear ity. For both younger (<45 years) and older (45; years) women, the opt imal change point for a single threshold model was found to be 21 kg/m .(2) Slopes of systolic BP on BMI above this threshold were positive a nd significant: 0.68 (95% CI, 0.54 to 0.81) and 0.53 (95% CI, 0.29 to 0.76) for younger and older women, respectively. Slopes below the thre shold were essentially zero for both groups of women, and the differen ce between the slopes above and below the threshold was significant fo r younger women (P=.019). In summary, we observed a threshold at 21 kg /m(2) in the relationship between BMI and BP for women but not for men . This contributes to the effort to identify the mechanisms that under lie this relationship and how they differ by gender.