Countries’ geographic latitude and their human populations’ cholesterol and blood pressure

Abstract

Background Sunlight has been hypothesized to play a role in variation in cardiovascular disease according to geographic latitude. Objectives To evaluate the plausibility of sunlight as a factor in populations’ average cholesterol and blood pressure Methods We analyzed World Health Organization data including 180 or more countries’ age-standardized average cholesterol, age-standardized mean systolic blood pressure (BP), and age-standardized prevalence of raised BP, by geographic latitude, over decades. We also performed analysis by ultraviolet B light (UVB) exposure. Results Mean cholesterol increases with the distance of a country from the Equator. This relationship has changed very little since 1980. Similarly, in 1975, mean systolic BP and prevalence of raised BP were higher in countries farther from the Equator. However, the relationship between latitude and BP has changed dramatically; by 2015, the opposite pattern was observed in women. Countries’ average UVB exposure has a stable relationship with cholesterol over recent decades, but a changing relationship with BP. Conclusions Since sunlight exposure in a country is relatively fixed and its relationship with BP has changed dramatically in recent decades, countries’ average sunlight exposure is an unlikely explanation for contemporary country-level variation in BP. However, our findings are consistent with a putative effect of sunlight on countries’ average cholesterol, as well as a no longer detectable effect on BP decades ago. A parsimonious potential explanation for the relationship between light and cholesterol is that 7-dehydrocholesterol can be converted to cholesterol, or in the presence of ultraviolet light, can instead be converted to vitamin D.