Vitamin D appears to do little to help stave off a cold or reduce the symptoms once one sets in, a new study suggests, despite its growing reputation as a tool to prevent a variety of illnesses and chronic disease.
Researchers in New Zealand say their study, conducted between February 2010 and November 2011, found that subjects who were given vitamin D supplements did not get fewer or less severe colds than subjects who received a placebo.
The researchers noted that studies have found an association between low vitamin D levels and respiratory tract infections. However, they also noted that research linking low vitamin D levels to a greater susceptibility to respiratory infections is thin.
Dr. David Murdoch of New Zealand鈥檚 University of Otago and colleagues recruited more than 320 healthy adults to participate in their study.
The subjects were randomly assigned to receive an initial dose of 200,000 International Units (IU) of oral vitamin D, another dose one month later, and then 100,000 IU monthly for 18 months, or a placebo on the same dosage regimen.
In the end, they found no statistical difference in the number of colds among the participants over the study period. There was an average of 3.7 colds per person in the group that received vitamin D and 3.8 colds per person in the placebo group.
Symptoms lasted for an average of 12 days in both groups, and subjects missed the same number of work days.
The researchers said the results remained the same when they factored in winter cold seasonand the baseline vitamin D levels of participants at the beginning of the study.
They do acknowledge that vitamin D may yet prove to be a useful tool for warding off colds.鈥淔urther research is required to clarify whether there is benefit from supplementation in other populations and with other dosing regimens,鈥� they conclude.
The findings are published in the Journal of the American Medical Association.
In an accompanying editorial, Dr. Jeffrey A. Linder of Boston鈥檚 Brigham and Women鈥檚 Hospital and Harvard Medical School noted that while there are many products available to relieve symptoms, there are no known proven preventive or curative treatments for colds.
According to Linder, vitamin D 鈥渋s an appealing agent to prevent respiratory tract infections鈥� because studies have shown that it can boost the immune system and protect against infection.
In his editorial, Linder made reference to the 2011 report from the Institute of Medicine, which recommended higher daily vitamin D intake for bone health, including increased bone density and reduced facture rates. The new recommendations called for most children and adults to get between 600 and 800 IU of vitamin D per day.
That report concluded that there was insufficient evidence that vitamin D offers benefits related to other health conditions, and made clear the daily dosage recommendations were solely for bone health.
The report did say that research showing an association between vitamin D and improved immune function, including the prevention of colds, warranted further study.
Linder writes that the New Zealand study 鈥渉as rigorously addressed this question,鈥� saying that vitamin D should be included among the therapies listed 鈥渁s being ineffective for preventing or treating upper respiratory tract infections in healthy adults.鈥�
However, in a commentary on the study, Dr. Aileen Burford-Mason, an immunologist and author of Eat Well, Age Better said the results only add to the confusion around vitamin D and its role in cold prevention.
She notes that starting levels of vitamin D in both the placebo and treatment group were 鈥渘ear normal,鈥� meaning none of the participants was deficient in the nutrient.
As well, Burford-Mason also notes that unlike drugs, nutrients like vitamin D do not work alone in the body to support its many systems. Subjects were allowed to take a multivitamin during the study, which may have boosted levels of other nutrients, which may have affected the results and 鈥渟hould have been controlled for.鈥�
鈥淭his study, then, does not tell us anything new about the role of vitamin D in preventing colds,鈥� Burford-Mason writes. 鈥淎ll it can do is remind us once again that nutrients are not drugs, and should not be studied as such.鈥�
