That blood pressure levels are higher during winter and further away from the equator has been known, but the reasons behind these observations had not been entirely clear so far.
Nitric oxide stored in the top layers of the skin reacts to sunlight and causes blood vessels to widen as the oxide moves into the bloodstream. That, in turn, lowers blood pressure. The skin has not been considered to be involved in blood pressure regulation so far. Exposure to ultraviolet light might help reduce the risk for heart disease. Among people with normal blood pressure, the effect of ultraviolet light is modest -- a drop in blood pressure of between 2 and 5 millimeters of mercury (mmHG). Avoiding sunlight or using sunblock constantly out of a fear of skin cancer could be a new risk factor for heart disease. This is not to suggest that people should sunbathe or use tanning beds in hopes of lowering blood pressure, however it is recommended that spending a moderate amount of time outdoors.
High blood pressure is a major risk factor for stroke and kidney disease, in addition to heart disease.
Note: This is experimemtal and should not be targeted as a main treatment for high blood pressure. Excessive exposure to sunlight carries the risk of developing skin cancer. more