Vitamin D has long been known as the sunshine vitamin because skin creates this hormone when exposed to ultraviolet light. However, winter in northern latitudes does not allow much vitamin D to be created. Research indicates that adequate vitamin D may improve the outcomes of assisted reproduction (Gaskins et al, American Journal of Obstetrics and Gynecology, online Feb. 8, 2019). Some evidence suggests that vitamin D supplements may also help reduce migraine frequency (Wells et al, Current Pain and Headache Reports, Feb. 21, 2019). On the other hand, the VITAL trial showed that vitamin D did not reduce cardiovascular disease or cancer. Consequently, many people wonder about the most appropriate dose and the best source for vitamin D.

Is Sunshine Really the Best Source for Vitamin D?

Q. When you think about supplementing vitamin D, your first choice should be sunshine, the most natural source. Vitamin D by itself doesn’t work; calcium, magnesium, phosphorus and iron are also necessary, along with vitamins A and K.

A. We love sunshine as a source of vitamin D, but there are circumstances when sun exposure isn’t practical. During the winter in most of the northern states, it is too cold and there isn’t enough sun to get vitamin D from sunshine on the skin. Even in the summertime, some people take medications that make them susceptible to sunburn. People with skin cancer must use sunscreens. They block vitamin D formation. There is still room for vitamin D supplements.

Other Supplements That Affect Vitamin D:

We think it does make sense to check your intake of magnesium as well as vitamin D. Additionally, some scientists propose that vitamin K2 is also important in the metabolism of vitamin D (Schwalfenberg, Journal of Nutrition and Metabolism, June 18, 2017). While we need vitamin D to absorb calcium well, we need vitamin K to get calcium into bones and keep it out of artery walls (Karpinski et al, Journal of the American College of Nutrition, July 2017). 

Over the course of the whole year, sunshine is an excellent source for vitamin D. Even certain individuals taking supplements of vitamin D3 have higher levels of 25-hydroxyvitamin D, the circulating form of this hormone, when they go out in the sun (O’Sullivan et al, Photochemistry and Photobiology, Jan. 16, 2019). We discuss dosing, signs of low vitamin D and home tests for vitamin D levels in our Guide to Vitamin D Deficiency

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