Questions and Answers About Vitamin D


The value of vitamin D supplementation is regularly debated.

The value of vitamin D supplementation is regularly debated.

Whenever I see my primary care physician, he asks me whether I’m taking a vitamin D supplement and insists on checking my serum vitamin D level. I think it’s time to take a look at some common questions and answers about vitamin D.

What does the evidence say about vitamin D’s health benefits?

There is ample evidence that vitamin D promotes bone health.

Along with calcium, vitamin D helps to protect older adults from bone loss. Vitamin D supplementation also appears to prevent falls in the frail elderly who are at risk for vitamin D deficiency.

Beyond bone health and possibly fall prevention, no other benefits for vitamin D supplementation have been proven.

Research comprised of mostly observational studies over the last 15 years suggests that adequate vitamin D levels might provide other benefits such as reduced risk for cardiovascular disease, cancer, diabetes, autoimmune diseases, and infectious respiratory diseases. Several large trials are underway to investigate the effects of vitamin D supplementation on outcomes such as cancer and cardiovascular disease.

Many health care providers promote vitamin D supplementation even in the absence of proven benefits. However, pharmacists must ensure that their recommendations are supported by strong clinical evidence.

Remember when vitamin E was deemed the magic elixir that was going to cure Alzheimer’s disease? Beta-carotene and selenium were also hyped in the past, but clinical trials demonstrated not only a lack of benefit, but also potential harm.

Can vitamin D supplementation treat depression or improve mood?

Virtually no evidence links vitamin D status to depression or related conditions.

Should health care providers regularly screen for vitamin D deficiency?

Most organizations do not recommend universal screening for vitamin D.

The US Preventive Services Task Force concluded that it could not determine the benefits or potential harms from vitamin D screening and early interventions. Furthermore, groups such as the Endocrine Society, the American Geriatrics Society, the American Academy of Pediatrics, and the American College of Obstetricians and Gynecologists have concluded that routine screening is not necessary.

In short, routine testing is a waste of health care resources.

Why do so many lab reports indicate a vitamin D deficiency?

There is no agreed-upon serum vitamin D level linked to health benefits. Therefore, laboratories often establish cut points based on their interpretation of the current literature.

An apparent increase in the prevalence of vitamin D deficiency is explained by the use of high cut points.

Are there concerns about vitamin D over-supplementation?

There is a common misconception that vitamin D supplementation is safe at any reasonable level, or that if some is good, then more may be better.

Vitamin D intake and serum 25-hydroxyvitamin D levels must be very high—perhaps 200 ng/mL to 400 ng/mL—to cause the classic toxicity of marked hypercalcemia and kidney and liver damage. There is also little concern about vitamin D supplementation at doses between 400 IU and 1000 IU per day.

However, concerns have been raised about supplementation in the range of 10,000 IU to 50,000 IU per day, which may be excessive.


Taylor CL, Thomas PR, Aloia JF, Millard PS, Rosen CJ. Questions About Vitamin D for Primary Care Practice: Input From an NIH Conference. Am J Med. 2015 Nov;128(11):1167-70.

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