Vitamin D and Colds: The Sequel

Some interesting and poorly-publicized developments regarding the benefits of vitamin D arrived at the end of the year. Specifically, the Institute of Medicine (IOM) released their long-awaited recommendations for supplemental D dosing, as well as their assessment of the growing body of vitamin D research. Commissioned by the US and Canadian governments, you can read the executive summary as well as view the table of doses by age group  — but don’t expect any wild conclusions.

A lot of folks were hoping the IOM would stretch the available data a little and create some controversial guidelines — imagine a Charlie Sheen/Lindsay Lohan hookup for the scientific community. But they played it much more Tom Hanks and Rita Wilson — solid, dependable, but let’s face it: nothing to make us race to the newsstands.

Vitamin D, as I mentioned in a previous post, has been touted as a preventive for everything from certain cancers to depression. As a result, some advisory groups recommend D in massive doses, with the goal of achieving high blood levels.

But a close review of the science shows most of these studies are associative at best. The New England Journal of Medicine, in an April 14, 2011 editorial, cautions:

“Association therefore cannot prove causation. Many micronutrients that seemed promising in observational studies (e.g., beta carotene, vitamins C and E, folic acid, and selenium) were not found to reduce cancer risk in randomized clinical trials, and some were found to cause harm at high doses.”

Until further data are available, steer clear of megadoses of vitamin D (those in excess of Institute of Medicine recommendations) and aim for a total 25(OH)D (also known as 25-hydroxyvitamin D) blood level of 20 ng/ml — despite what other groups might advise.

On to the common cold….

It’s still mighty chilly in Portland, and that means we’re all inside more and passing germs around with greater ease. If it makes you feel any better, not even your doctor has been spared. The Baskin household has been a rhinovirus revolving door since November.

A recently-published meta-analysis revived interest in zinc, the nutritional supplement that (in nasal form) was associated with numerous cases of anosmia a few years back. In response, the maker, Matrixx, pulled the formulation, while maintaining its safety.

But the oral form of zinc was never implicated, and remains on the market. The new study summarizes all available information since 1984 on zinc and colds, and offers the following conclusions:

  • Zinc is an effective cold remedy in adults and children, shortening duration and severity of cold symptoms if taken within 24h of symptom onset.
  • When used as a preventive in school-age children, zinc also reduces absenteeism associated with colds.
  • If taken continuously for 5 months, zinc cuts cold frequency by about a third.
  • No one knows how zinc works to fight cold viruses.
  • Zinc causes mild-to-moderate side effects, including bad taste, nausea, constipation, diarrhea, abdominal pain, dry mouth and oral irritation.
  • Studies used a wide variety of formulations (zinc gluconate or acetate lozenges, zinc sulfate syrup) and dose ranges (30 to 160 mg/day), so the optimal regimen is unknown.

This meta-analysis was conducted by the highly respected Cochrane Group, so I’m inclined to trust the methodology.

Whether it’s worth it to take a pill that tastes bad, causes a fair number of side effects and reduces cold duration by only a day is up to the consumer. For individuals who catch a lot of colds, that one-third reduction in cold frequency might be sufficient reward to suffer through preventive treatment for a season.

As for me, I’ll stick with chicken soup.

Posted in Medical Blog Posts. RSS 2.0 feed.

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