Association of sun and UV exposure with blood pressure and cardiovascular disease: A systematic review

Background: Ecological studies show that sun or ultraviolet (UV) exposure have inverse associations with blood pressure (BP) and cardiovascular disease (CVD). Although sunlight is the primary source of vitamin D, recent meta-analyses of clinical trials have not reported a beneficial effect from vitamin D supplementation on BP or CVD. Sunlight may have beneficial effects independent of vitamin D. We carried out a systematic review to appraise the extent and quality of the evidence from human studies. Methods: Observational and interventional studies that measured sun or UV exposure, along with BP or CVD, were selected after searching databases. Results: Identified studies could not be combined quantitatively in meta-analysis because of different exposure measures. Solar exposure was inversely associated with BP in 3 out of 4 cross-sectional publications, and with CVD and/or total mortality in 5 out of 6 publications of cohort studies. Two of the cohort studies reported inverse associations between sun exposure and CVD, after adjusting for serum 25-hydroxyvitamin D. Five clinical trials with an appropriate control group were identified, the outcome being BP. Two trials compared UVB with UVA (as control), with only one finding a significant reduction in BP (after 6 weeks). Three trials compared short-term UVA exposure (< 30 min) with placebo (or crossover control), of which two reported short-term lowering of BP. Conclusion: This review has identified a small body of evidence that suggests sun exposure protects against high BP and CVD, but further research is required to determine if this is independent of vitamin D.