Vitamin D controversies examined

Issue: April 2011

Since the Institute of Medicine’s report on Dietary Reference Intakes for Calcium and Vitamin D was released in November 2010, vitamin D has been the subject of controversy.

To address these topics of controversy, Richard Gallo, MD, PhD, reviewed some of the issues: 15 minutes of sunlight a day provides adequate vitamin D; vitamin D improves bone health; vitamin D protects against cancer; and vitamin D improves immune function.

Gallo, who spoke last week during the 69th Annual Meeting of the American Academy of Dermatology, highlighted a 1991 Danish study published in the British Journal of Medicine.

There is no reason to suspect that sunshine is not in some way associated with serum 25-hydroxyvitamin D, or 25(OH)D, levels. However, further examination of the study revealed interesting observations, including that most patients with sun-seeking behavior still had less than optimal serum vitamin D. More than 53% with sun-seeking exposure had serum 25(OH)D levels of less than 50 nmol/L, Gallo said in a press release.

A 2009 study of serum 25(OH)D levels in twins during the summer and winter provided additional evidence regarding sun exposure.

“Presumably, these pairs had relatively similar sun exposures, but there’s tremendous variability within this population in terms of their actual levels. It was concluded that 50% of this variation, particularly in the summer season, was more due to genetic influences than to sun exposure,” said Gallo, who is professor of medicine and pediatrics and chief of the division of dermatology at the University of California, San Diego.

He said the 2008 American Journal of Clinical Nutrition study by Cashman that looked at oral intake is also applicable to sun exposure as a source of intake. Although serum 25(OH)D levels increased, the relationship between dose and 25(OH)D was not linear.

Other data from a 2010 Journal of the American Medical Association study of women aged 70 years and older who received a single annual high dose of vitamin D showed a higher rate of falls and fractures compared with women who received placebo.

“Vitamin D improves bone health; however, there is still more to learn,” Gallo said.

Regarding whether vitamin D protects against cancer, Gallo said the 2009 Agency for Healthcare Research and Quality (AHRQ) Evidence Report, “Vitamin D and Calcium: A Systematic Review of Health Outcomes,” showed that the association between colon cancer and serum 25(OH)D levels varied with regard to increase and decrease of cancer risk in some individual studies.

According to Gallo, observations in tissue cultures systems and mouse models led to the biological plausibility that levels of vitamin D may improve resistance to infections.

“When you start to look at some of the human studies, you see that some are seasonal associations with viral infections of [upper respiratory infections], and that can be associated with the serum levels of 25-D,” Gallo said.

Although the evidence looks convincing, he said, few studies in the AHRQ Report concur. Observational studies associate tuberculosis with genetic polymorphisms in the vitamin D receptor. Only small clinical trials support association between change in immune function and vitamin D, and randomized controlled trials have not shown a clear protective effect against infection by vitamin D supplementation, according to Gallo.

“Vitamin D may protect against infection, but it is still too soon to know how or when,” he said.

The American Academy of Dermatology recently updated its position statement on vitamin D based on the IOM report. The position statement reflects the IOM’s findings, including the vitamin D blood level deemed adequate and safe for the human body (20 ng/mL), and the recommended dietary allowance for calcium and vitamin D intake to support skeletal health. The academy noted that the recommended dietary allowance for vitamin D reflect an assumption of minimal sun exposure.

For more information:

Gallo R. Hot topics. Presented at: The American Academy of Dermatology 69th Annual Meeting; Feb. 4-8, 2011; New Orleans.

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