Mega-doses of vitamin D once per month did not reduce the number of upper respiratory tract infections (URTIs), compared to placebo, but would differences have been observed in people with lower levels?
New data published in the Journal of the American Medical Association (JAMA) indicated that a monthly dose of 100,000 IUs of vitamin D3 for 18 months was associated with the same number of URTIs per participant, the duration of symptoms, and the number of days of missed work as the placebo group.
In an accompanying editorial, Jeffrey Linder, MD, from Brigham and Women’s Hospital and Harvard Medical School, Boston, said the results of the VIDARISstudy “suggest that vitamin D should join the therapies listed in the Cochrane reviews as being ineffective for preventing or treating upper respiratory tract infections in healthy adults.”
However, such conclusions were challenged by renowned vitamin D researcher Michael Holick PhD, MD, from Boston University Medical Center. Dr Holick told NutraIngredients-USA: “This trial showed that people who were already vitamin D sufficient did not receive an additional benefit from vitamin D supplements.”
The average blood levels of vitamin D of the study participants at the start of the study – measured by 25-hydroxyvitamin D (25-OHD) levels - was 29 ng/mL. Sufficient levels are 30 ng/mL or above.
The new study should not mean that people stop taking vitamin D supplements, said Dr Holick. “What we still do not know is whether supplements of vitamin D would alter the rate of upper respiratory tract infections in people with deficient or insufficient levels of the vitamin.”
Dr Holick added that the evidence suggested it would since it is well-known that children with rickets had significantly higher incidences of upper respiratory tract infections.
This point was noted by the authors of the VIDARIS study - David Murdoch, MD, et al. from the University of Otago in New Zealand: “It is possible that an effect may be observed in a population with a higher prevalence of vitamin D deficiency, as occurred in a recent trial of vitamin D supplementation to reduce exacerbations of chronic obstructive pulmonary disease.
“In that trial, vitamin D supplementation significantly reduced exacerbations only in patients with baseline 25-OHD levels less than 10 ng/mL.”
Cara Welch, PhD, Sr VP, scientific & regulatory affairs for the Natural Products Association (NPA) told this website: “We’ve seen vitamin D supplementation have a beneficial effect on those who are truly deficient and this study is not set up to change this understanding.
“The investigation of vitamin D will continue and I would expect to see follow-up studies looking at daily intakes as opposed to monthly administrations or looking at populations who are truly vitamin D deficient.
“In the meantime, consumers should not be dissuaded from taking vitamin D supplements.”
Dr Murdoch and his co-workers followed 322 healthy people in New Zealand from February 2010 until November 2011. Participants were randomly assigned to receive an initial dose of 200,000 IU oral vitamin D3, then 200,000 IU one month later, then 100,000 IU or placebo every month for 18 months.
Results showed that average 25(OH)D levels increased from an initial level of 29 ng/mL to 48 ng/mL in the vitamin D group.
During the course of the study, 593 URTI episodes were documented in the vitamin D group and 611 in the placebo group.
Statistically, there were no significant differences in the average number of URTIs per participant (3.7 per person in the vitamin D group and 3.8 in the placebo group), the average duration of symptoms per episode (12 days in each group), and the average number of days of missed work as a result of URTIs.
In his editorial, Dr Linder added: “The VIDARIS trial, which assessed upper respiratory tract infections as they actually occur in the real world, demonstrated that vitamin D supplementation does not reduce the incidence of respiratory tract infections in adults who have sufficient levels of 25-OHD.
“In developed countries, for bone health, most persons should already have daily vitamin D intake sufficient to achieve adequate 25-OHD levels. Those seeking preventive interventions for the common cold are likely to be similar to the participants in the VIDARIS trial.”
2012, Volume 308, Number 13, Pages 1333-1339, doi:10.1001/jama.2012.12505
“Effect of Vitamin D Supplementation on Upper Respiratory Tract Infections in Healthy Adults: The VIDARIS Randomized Controlled Trial”
Authors: D.R. Murdoch, S. Slow, S.T. Chambers, et al.
2012, Volume 308, Number 13, Pages 1375-1376, doi: 10.1001/jama.2012.13130
“Vitamin D and the Cure for the Common Cold”
Authors: J.A. Linder