A recent study suggest that it may not be the vitamin D that reduces cardiovascular disease. (3) In a Tedx Talk that can be found below Richard Weller discusses the research that Vitamin D status might just be a marker for sunlight exposure. The sunlight exposure itself may have cardiovascular benefits, even without increases in vitamin D levels.
The research has found that our skin contains large stores of nitrate, nitrite and several reactive nitrogen oxide species. When the skin is exposed to UV rays from the sun, these stores are converted to nitric oxide. They have shown that 30 minutes of sun exposure can increase circulating nitrite, lower blood pressure and increased blood flow. Nitric oxide is a vasodilator which lowers blood pressure. Nitrite not only dilates blood vessels but also protects organs against ischaemia/reperfusion (I/R) damage. (4)
Chris Masterjohn stated at his website Cholesterol-and-Health:
"Endothelial cells produce nitric oxide, a gas that protects LDL from oxidation, increases blood flow, decreases the adhesion of monocytes to the endothelium, and decreases blood clotting. Oxidized LDL impairs the endothelial cell's ability to produce nitric oxide" (5)
Vitamin D may very well have its own benefits when it comes to cardiovascular disease. While supplementing with D3 may be beneficial at times of the year when we do not get enough sunlight, this study demonstrates that we would be better off getting our vitamin D from the sun. It is always better to get nutrients from natural sources as much as possible. Whole foods, as well as sunshine, may have benefits that we have not yet identified. Supplements can supply some nutrients, but we miss out on all the unknown benefits found in nature.
This study also emphasizes why observational studies should be the starting point in science, not the end point. If these researchers had just accepted the epidemiology and concluded it must be just the vitamin D protecting against heart disease they would not have made this discovery. Not only do you risk giving credit or blame where it is not warranted, you miss the opportunity to ask the question, "What else could be causing this effect?"