The effects of two different doses of ultraviolet-A light exposure on nitric oxide metabolites and cardiorespiratory outcomes

Purpose
The present study investigated different doses of ultraviolet-A (UV-A) light on plasma nitric oxide metabolites and cardiorespiratory variables.

Methods
Ten healthy male participants completed three experimental conditions, 7 days apart. Participants were exposed to no light (CON); 10 J•cm² (15 min) of UV-A light (UVA10) and 20 J•cm² (30 min) of UV-A light (UVA20) in a randomized order. Plasma nitrite [NO₂^-] and nitrate [NO₃^-] concentrations, blood pressure (BP), and heart rate (HR) were recorded before, immediately after exposure and 30 min post-exposure. Whole-body oxygen utilization (V̇O₂) and skin temperature were recorded continuously. 

Results
None of the measured parameters changed significantly during CON (all P>0.05). V̇O2 was significantly reduced immediately after UVA10 (P=0.03) despite no change in plasma [NO₂^-] (P>0.05). Immediately after exposure to UVA20, plasma [NO₂^-] was higher (P=0.014) and V̇O2 tended to be lower compared to baseline (P=0.06). There were no differences in [NO₂^-] or V̇O2 at the 30 min time-point in any condition. UV-A exposure did not alter systolic BP (SBP), diastolic BP or MAP (all P>0.05). V̇O2 was significantly reduced immediately after UVA10 (P=0.03) despite no change in plasma [NO₂^-] (P>0.05). There were no differences in [NO₂^-] or V̇O2 at the 30 min time-point in any condition. UV-A light did not alter plasma [NO₃^-] at any time point (all P>0.05).

Conclusions
This study demonstrates that a UV-A dose of 20 J•cm² is necessary to increase plasma [NO₂^-] although a smaller dose is capable of reducing V̇O2 at rest. Exposure to UV-A did not significantly reduce BP in this cohort of healthy adults. These data suggest that exposure to sunlight has a meaningful acute impact on metabolic function.