Vitamin D is for "doesn't do diddly" for the common cold (RCT) - PulmCCM
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Oct 262012
 
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Extra Vitamin D Doesn’t Prevent Colds in Healthy Adults (JAMA)

It looks like you can add Vitamin D to list of supplements (echinacea, vitamin C, etc.) who’ve gone up against the common cold and lost. (Scorekeepers will note that zinc held its own, though, in a Cochrane analysis.)

Vitamin D plays an important role in immune responses, most significantly by inducing cathelicidins, specialized antimicrobial proteins made by white blood cells which are necessary for fighting infections. Although the cathelicidins are best-known for their antibacterial effects, they seem to help against viruses, too. Seeking to harness this natural antibiotic mechanism, investigators have been testing vitamin D supplementation in numerous infections. The results have mostly been disappointing, but a recent randomized trial showed vitamin D supplementation accelerates recovery from  tuberculosis.

The existing trials testing vitamin D supplementation to prevent the common cold were relatively low quality and had conflicting results. David Murdoch, Sandy Slow, Robert Scragg et al fixed that with the publication of their VIDARIS trial in the October 3 JAMA, concluding that giving healthy adults with essentially normal vitamin D levels (mean 29 ng/mL) high doses of vitamin D for 18 months (400,000 IU orally over 2 months, then 100,000 IU / month) did not reduce the number or severity of upper respiratory tract infections (colds) compared to placebo.

The 322 participants in Christchurch, New Zealand got ~3.7 colds during the year-and-a-half follow-up period, regardless of treatment assignment. (The URIs were defined through symptoms, and nasopharyngeal swabs were collected and confirmatory in a minority of participants.)

People missed 0.76 days of work on average, had 12 days of symptoms, and equal severity of symptoms between groups, as well. The people with the lowest vitamin D levels at baseline did not gain a benefit from vitamin D supplements, when analyzed separately. There were no detected episodes of hypercalcemia or other adverse events.

Only 5 of their participants had baseline vitamin D levels less than 10 ng/mL, so it’s still possible that vitamin D supplementation could prevent upper respiratory or other infections in people with true vitamin D deficiency.

This study tested vitamin D supplementation in healthy people with normal levels (depending on your definition) at baseline. Low baseline serum vitamin D or vitamin D deficiency has been linked to many chronic conditions, including chronic obstructive pulmonary disease (COPD), asthma, diabetes, hypertension, and numerous cancers. Vitamin D deficiency and critical illness are also associated.

It has never been clear, though, whether low vitamin D levels are a contributor to these illnesses and their severity, or if vitamin D levels just fall for some reason during chronic illness, without real clinical significance. To my knowledge, randomized trials have not yet shown any consistent benefit of vitamin D supplementation for people with vitamin D deficiency and asthma, COPD or other chronic illnesses, with the possible exception of osteoporosis.

David R. Murdoch et al. Effect of Vitamin D Supplementation on Upper Respiratory Tract Infections in Healthy Adults. The VIDARIS Randomized Controlled Trial. JAMA 2012; 308: 1333-1339.

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  2 Responses to “Vitamin D is for “doesn’t do diddly” for the common cold (RCT)”

  1. Was unaware that vitamin D was meant to prevent COPD exacebations. I have IPF, however I take it with Calcium for osteoporosis. I do take large doses of Vitamin C however, have done for many years, and have not had a head cold for as long back as I can remember. (tend to have bronchial problems intermittently due to the IPF and taking immune suppressants). In my childhood, teens and early 20s I had so many colds and chest infection during each year it was unbelievable. After starting on Vitamin C I did not have another cold for over 3yrs, and then by increasing the dosage of Vitamin C, it lasted less than 24hrs. No Doctor will ever convince me that Vitamin C does not work!

  2. If no doctor (and presumably no scientist) will ever convince you that vitamin C doesn’t work, you aren’t doing science. Nothing wrong with that, but you can’t claim your beliefs are justified (by science anyway). Fortunately vitamin C is easily excreted in urine and relatively cheap so the risks are low.

    Note that high doses of vitamin C have an antihistamine effect, so it’s quite possible you are getting just as many infections as you were before but the symptoms are supressed. Other options include a maturing immune system, reduced exposure (children are far more exposed to other sick children than adults are) and observation bias.

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