A little time in the sun can do more than just give you a tan; it may help reduce your blood pressure. The incidence of hypertension and cardiovascular disease correlates with latitude and increases during winter, and researchers from the University of Edinburgh set out to find out why. They hypothesized that the seasonal and latitudinal associations with hypertension could be related to the effects of the sun’s UV radiation on nitric oxide (NO) in the skin, in light of the fact that NO metabolites are abundant in human skin. In the body, NO typically has a vasodilating effect, facilitating blood flow and reducing blood pressure.
In 24 healthy volunteers, irradiation of the skin with UVA lowered blood pressure with decreases in circulating NO and increases in NO metabolites. Dietary interventions to increase circulating NO had no effect on these UVA-induced changes, which suggests that the blood pressure reduction was the result of activity of NO stored in the skin, rather than direct utilization of circulating NO. The study authors concluded that “our data provide mechanistic insights into an important function of the skin in modulating systemic NO bioavailability which may account for the latitudinal and seasonal variations of BP and cardiovascular disease.”
Liu D, Fernandez BO, et al. UVA Irradiation of Human Skin Vasodilates Arterial Vasculature and Lowers Blood Pressure Independently of Nitric Oxide Synthase. J Invest Dermatol. 2014 Jan 20. doi: 10.1038/jid.2014.27.