Blood pressure and body mass index in lean rural and semi-urban subjects in West Africa.

BACKGROUND Blood pressure (BP) is positively related to body mass index (BMI) in persons of both Caucasian and African origin, but the precise nature of the relationship is unclear. OBJECTIVE To study the relationship between BP and BMI in a lean African population. DESIGN A community-based cross-sectional study. METHODS The BMI and BP were measured in 362 men and 592 women aged 40-75 years living in Ashanti, Ghana. In total, 498 lived in semi-urban areas and 456 in rural villages. RESULTS The BMI was higher among semi-urban women [23.1 kg/m (95% confidence interval (CI), 22.5 to 23.6)] than semi-urban men [20.9 kg/m (95% CI, 20.6 to 21.5)], rural men [19.5 kg/m (95% CI, 19.1 to 19.9)] and rural women [19.9 kg/m (95% CI, 19.5 to 20.3)]. For systolic BP in women older than 52 years and in semi-urban women, the relationship was non-linear. The slope of the line below the change point ("knot") was greater than that above it. There was no evidence of non-linearity in men. For diastolic BP only younger women had a significant "knot" point at 18 kg/m. Again, the slope of the line below the "knot" was greater than that above it. In men, however, there was also evidence of a "knot" in younger and rural men, with the slope of the line below the "knot" being less that that above it (unlike in women). CONCLUSIONS The relationship between BP and BMI is not linear, and is possibly sigmoid, but this may vary between subgroups.