JAMA Study Finds Vitamin D Doesn't Reduce Colds

CHICAGOVitamin D3 Supplementation did not reduce the incidence or severity of colds in healthy adults, according to a new study conducted at the University of Auckland, New Zealand (JAMA. 2012;308[13]:1333-1339). However, the supplement industry reminded that supplements are not likely to cure or prevent colds.

"I hope that we don't get misguided media articles that say 'vitamin D doesn't work,' because that's not what the author says, and it's not what the science says," said Duffy MacKay, N.D., vice president, scientific and regulatory affairs, Council for Responsible Nutrition (CRN). "Keeping vitamin D levels in the normal range is of vital importance. Most would agree supplementation is the most reliable and safe way to obtain vitamin D. "

MacKay said vitamin Dor any other supplement or drugwill likely not reduce colds. "The cure for the common cold has been a elusive target for literally centuries," he said. "It's important for healthy people to catch colds because it's how we exercise our immune systems. For the next couple of hundred years, we're probably going to realize the best cure for the common cold is chicken soup and rest."

Instead, Mackay said it would be better to look at what other roles vitamin D plays in immune health. He said many of observational studies show vitamin D can help reduce autoimmune disorders, chronic low immunity and overactive immune systems. "I'm hoping that we get more randomized trials that look at more interesting aspects of the immune system," he said.

Study Details

In this randomized, double blind, placebo-controlled trial, 322 healthy adults received an initial dose of 200,000 IU of oral vitamin D3, then 200,000 IU one month later, and then 100,000 IU each month for the next 16 months (n=161), or placebo administered in an identical dosing regimen (n=161) between February 2010 and November 2011 in Christchurch, New Zealand.

Throughout the 18-month trial, the vitamin D supplementation group had 593 upper respiratory tract infections (URTIs), and the placebo group had 611, with no statistically significant differences in the number of URTIs per participant (mean, 3.7 per person in the vitamin D group and 3.8 per person in the placebo group), number of days of missed work as a result of URTIs (mean, 0.76 days in each group), duration of symptoms per episode (mean, 12 days in each group) or severity of URTIs.

Study Implications

One reason the vitamin D supplementation may not have affected immunity in this study was that mean serum 25-hydroxyvitamin D (25-OHD)  level of participants at the beginning of the study was 29 ng/mL. The National Institutes of Health (NIH) says vitamin D levels higher than 20 ng/mL are generally considered adequate for bone and overall health. In this study, vitamin D supplementation resulted in an increase in serum 25-OHD levels that was maintained at greater than 48 ng/mL throughout the study; the NIH says 25-OHD levels higher than 50 ng/mL may be toxic.

Mackay said people with adequate vitamin D levels are unlikely to see cold-reducing benefits from raising their levels. In contrast, he noted a recent study that found vitamin D supplementation at the low dose of 300 IU/d significantly reduced the risk of acute respiratory tract infections in children with vitamin D deficiency.

Cara Welch, Ph.D., senior vice president, scientific and regulatory affairs, Natural Products Association (NPA), agreed and added, "Studies have shown that vitamin D supplementation has a beneficial effect on those truly deficient, and this particular study is not designed to address this. Research into vitamin D will continue, and I expect to see follow-up studies looking at daily intakes, not just monthly administrations, or looking at populations who are truly vitamin D deficient. For now, consumers should not be deterred from taking their vitamin D supplements."

A good piece of news from this study, according to Mackay, was that subjects received a high level of vitamin D at once, but did not experience adverse effects. "When the Institutes of medicine (IOM) revisited their recommendations for vitamin D and calcium, it set an upper limit of 4,000 IU/d of vitamin D," he said. "With more studies like this with really high doses, we may see comfort with using higher doses."

A 2010 study from the University of Copenhagen  reported vitamin D is crucial to activating the bodys immune defenses to help people fight off serious, life-threatening infections.  And earlier this year, two studies reported vitamin D deficiency may be linked to severe illness in children.