Exposure to sunlight causes arterial vasodilation and lowers blood pressure (BP), according to research published online in the Journal of Investigative Dermatology.

Donald Liu, MB, ChB, PhD, of the University of Edinburgh in the United Kingdom, and colleagues exposed the skin on the forearms of 24 participants to ultraviolet A (UVA) wavelengths of sunlight to investigate the effects of UVA on nitric oxide (NO) availability and the resulting cardiovascular effects.

The researchers found that exposure to UVA lowered BP, with concomitant decreases in circulating nitrate and increases in nitrite concentrations. Because dietary intervention to modify the availability of systemic nitrate did not affect these UV-induced hemodynamic changes, it appears that they are not mediated by the direct utilization of circulating nitrate. UVA irradiation of the forearm increased blood flow independently of NO-synthase activity, indicating that pre-formed cutaneous NO stores were involved. Studies with confocal fluorescence microscopy revealed that UVA irradiation causes NO-synthase-independent, dose-dependent release of NO. The majority of light-sensitive NO was pooled in the upper epidermis.

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“Collectively, 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,” the authors concluded.