Despite the fact that higher vitamin D levels are nearly always found to be related to reduced risk of cardiovascular disease and associated diseases such as diabetes mellitus, randomized controlled trials have not found that vitamin D supplementation reduces risk of cardiovascular disease.
Therefore, vitamin D levels are likely a surrogate measurement for sun exposure, meaning that some other photoproduct such as nitric oxide (NO) may be responsible for the lowered risk of CVD. A pair of recent papers reported that leisure-time or recreational outdoor physical activity was significantly associated with reduced risk of cardiovascular disease. In a study in the U.S., both frequency and intensity of outdoor activities were associated with reduced risk, as was higher vitamin D level. When vitamin D levels were removed from the equation, an inverse association was still found between outdoor recreational activity and mortality. The authors stated the following: “The underlying mechanism for this association may not involve 25(OH)D hence, further studies are warranted to confirm and investigate the underlying mechanism.” I would suggest that nitric oxide was the protective photoproduct, produced by sun exposure, which lessened the risk of CVD with outdoor activity.
Similar findings have been found for hypertension, diabetes mellitus, heart failure, stroke, and myocardial infarction (heart attack). In a study in Finland, older adults who had moderate leisure-time activity had 30-40% reduced mortality and cardiovascular disease rates than those with low activity levels, while those with high activity levels had 50% lower rates.
Two messages from this research: (1) Start living more of your life outdoors. (2) Be sure to obtain plenty of non-burning sun exposure during you outdoor activity. Your life may depend on it.
 Wang L, Song Y, Manson JE, Pilz S, März W, Michaëlsson K, Lundqvist A, Jassal SK, Barrett-Connor E, Zhang C, Eaton CB, May HT, Anderson JL, Sesso HD. Circulating 25-hydroxy-vitamin D and risk of cardiovascular disease: A meta-analysis of prospective studies. Circ Cardiovasc Qual Outcomes. 2012 Nov 1;5(6):819-29.
 Song Y, Wang L, Pittas AG, Del Gobbo LC, Zhang C, Manson JE, Hu FB. Blood 25-hydroxy vitamin D levels and incident type 2 diabetes: a meta-analysis of prospective studies. Diabetes Care. 2013 May;36(5):1422-8.
 Veloudi P, Jones G, Sharman JE. Effectiveness of vitamin D supplementation for cardiovascular health outcomes. Pulse 2016;4:193-207 https://www.karger.com/Article/FullText/452742
 Donneyong MM, Taylor KC, Kerber RA, Hornung CA, Scragg R. Is outdoor recreational activity an independent predictor of cardiovascular disease mortality – NHANES III? Nutr Metab Cardiovasc Dis. 2016 Aug;26(8):735-42.
 Barengo NC, Antikainen R, Borodulin K, Harald K, Jousilahti P. Leisure-Time Physical Activity Reduces Total and Cardiovascular Mortality and Cardiovascular Disease Incidence in Older Adults. J Am Geriatr Soc. 2016 Dec 26. doi: 10.1111/jgs.14694. [Epub ahead of print]