DECODING THE HYPE: Vitamin D—a Bone of Contention?

Posted by The Evidence Blog on December 26, 2013

THE CONTROVERSY
Vitamin D is a hot topic in science, with studies suggesting various levels as a cause or a cure of illnesses ranging from cancer to multiple sclerosis. However, aside from bone health, the role of vitamin D in nonskeletal conditions is not really clear. In the United States, almost half of all U.S. adults take vitamin D supplements to the tune of $600 million per year.

Last week, a study published in one of the Lancet journals reported that vitamin D is more likely to be a marker of poor health, rather than a cause of any one disease itself. The study also suggests that supplementation may not reduce the risk in deficient patients if the dose is too low. To clarify some of this confusion, Hayes is happy to offer the following perspective.

THE EVIDENCE
The study, which appeared in The Lancet Diabetes & Endocrinology, was a review of 172 randomized controlled trials (RCTs) that studied the effect of vitamin D concentrations on nonskeletal health outcomes in adults older than 18 years of age. They compared these results with 290 observational studies to learn more about any purported gaps in the findings from the observational studies and the RCTs. All of the studies included in the analysis used blood levels of 25-hydroxyvitamin D to measure vitamin D sufficiency/insufficiency. Although the RCTs used various doses of vitamin D supplements, most of them used at least 800 units.

Here’s what they found.

  • In general, observational studies of people with high vitamin D levels showed more robust results than the RCTs in disorders related to cardiovascular disease, inflammation, glucose metabolism, infectious disease, disorders of mood and cognition, and all-cause mortality.
  • Observational studies showed no similar association, even in those patients who underwent vitamin D supplementation at baseline.
  • In 34 of the RCTs, a large number of participants did not show improved outcomes after taking 50 mcg of vitamin D daily. The exception was older women, who were able to reduce their all-cause mortality with 20 mcg/day of vitamin D supplements.
  • In 16 studies of vitamin D in patients with type 2 diabetes, vitamin D supplementation did not reduce HbA1c, a biomarker for diabetes control.

The researchers concluded that vitamin D deficiency is likely a marker of ill health, rather than a cause. They propose that all of the conditions noted above are associated with inflammation, which would reduce vitamin D levels.

THE BOTTOM LINE
There are several reasons why the RCTs found no link between vitamin D supplementation and disease prevention.

  • No link exists and the findings are true.
  • RCT participants did not have vitamin C levels low enough to benefit from supplementation.
  • The dose of vitamin D provided was too low.
  • The dose of vitamin D was not provided over a long enough period of time.

It is important to remember that this study did not focus on the role of vitamin D in bone health—only on the effects of diseases not affecting bone. The researchers report that such research is underway and may be ready in 2017.

In the meantime, the Institute of Medicine suggests that the majority of Americans are already taking in enough vitamin D without requiring supplements. They recommend that most Americans under the age of 70 years need no more than 600 IU of vitamin D daily to keep their bones healthy—an amount that seldom requires supplementation. Vitamin D is readily available in fortified products and from natural sunlight.

  1. Autier P, Boniol M, Pizot C, Mullie P. Vitamin D status and ill health: a systematic review. Lancet Diabetes Endocrinol. 2014;2(1):76-89. Epub ahead of print. December 6, 2013. Abstract available at: http://www.thelancet.com/journals/landia/article/PIIS2213-8587%2813%2970165-7/abstract. Accessed December 18, 2013.

Topics: Hayes Blog

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