Relationship between blood pressure and body mass index in lean populations

ABSTRACT

Associations between body mass index (BMI) and blood pressure (BP) have been consistently observed, but remain poorly understood. One unresolved question is whether there is a linear relationship across the entire BMI range. We investigated this question among 11235 adult men and women from seven low-BMI populations in Africa and the Caribbean. We used kernel smoothing and multivariate linear and spline regression modeling to examine gender differences in the relationship and to test for a threshold. Age-adjusted slopes of BP on BMI were uniformly higher in men than women, with pooled slopes ratios of 2.00 and 2.20 for systolic and diastolic BPs, respectively. Men displayed no evidence of age modification or nonlinearity in the relationship, and the age-adjusted slope of systolic BP on BMI was 0.90 (95 percent confidence interval [CI], 0.76 to 1.04). Women demonstrated both age modification and nonlinearity. For both younger (<45 years) and older (45+ years) women, the optimal change point for a single threshold model was found to be 21kg/m. Slopes of systolic BP on BMI above this threshold were positive and significant 0.68 (95 percent CI, 0.54 to 0.81) and 0.53 (95 percent CI, 0.29 to 0.76) for younger and older women, respectively. Slopes below the threshold were essentially zero for both groups of women, and difference between the slopes above and below the threshold was significant for younger women (P=.018). In summary, we observed a threshold at 21kg/m in the relationship between BMI and BP for women but not for men. This contributes to the effort to identify the mechanism that underlie this relationship and how they differ by gender.(AU)