Vitamin D & influenza - randomized trial

Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren:

Design: From December 2008 through March 2009, we conducted a randomized, double-blind, placebo-controlled trial comparing vitamin D3 supplements (1200 IU/d) with placebo in schoolchildren. The primary outcome was the incidence of influenza A, diagnosed with influenza antigen testing with a nasopharyngeal swab specimen.

Results: Influenza A occurred in 18 of 167 (10.8%) children in the vitamin D3 group compared with 31 of 167 (18.6%) children in the placebo group [relative risk (RR), 0.58; 95% CI: 0.34, 0.99; P = 0.04]. The reduction in influenza A was more prominent in children who had not been taking other vitamin D supplements (RR: 0.36; 95% CI: 0.17, 0.79; P = 0.006) and who started nursery school after age 3 y (RR: 0.36; 95% CI: 0.17, 0.78; P = 0.005). In children with a previous diagnosis of asthma, asthma attacks as a secondary outcome occurred in 2 children receiving vitamin D3 compared with 12 children receiving placebo (RR: 0.17; 95% CI: 0.04, 0.73; P = 0.006).

I will attest to improvement in my own respiratory health since I began taking vitamin D supplements in 2007, but more studies need to be done to confirm that this is a robust finding.

Citation: Am J Clin Nutr (March 10, 2010). doi:10.3945/ajcn.2009.29094

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Maybe the relavent question is: Does enough evidence exist now for public health officials to recommend that doctors start checking their patients' vitamin D status? Here's another recent study:

Vitamin D Required for T cell Activation

"For the research team, identifying the role of vitamin D in the activation of T cells has been a major breakthrough. âScientists have known for a long time that vitamin D is important for calcium absorption and the vitamin has also been implicated in diseases such as cancer and multiple sclerosis, but what we didnât realize is how crucial vitamin D is for actually activating the immune system â which we know now."

The study you link to used 1200iu/daily.

Circulating 25-Hydroxyvitamin D Levels in Fully Breastfed Infants on Oral Vitamin D Supplementation
This paper shows it generally takes 100iu/daily per 2.5lbs or 1000iu/daily per 25lbs to raise status sufficiently for breast milk to flow vitamin d replete and babies to develop optimum bone mineral density. 1200iu/daily is probably an ideal amount for a kid weighing 35lbs. The average schoolkid getting only 1200iu/daily will remain vitamin d insufficient.
Similarly it usually takes 3 months to replete D3 status. This trial stopped at 3 months. As Vitamin D3 production in the skin is reduced in those with higher 25(OH)D status it is safe to take up to 10,000iu/daily (kids half that amount) and still go out in the sunshine. As vitamin D3 improves the natural photo-protection of the skin it is worth improving status BEFORE regular sunbathing. It is also worth continuing taking D3 through the summer so by the Autumn you have a STORED reserve of D3 to improve your immune function through the winter. We only begin to store D3 above 42ng/ml 110nmol/l. and only about 150nmol/l 60ng/ml do we find least incidence of chronic illness.

Hi there,

There is a wealth of information on this topic at the Vitamin D Council's website:

Since interviewing Dr. John Cannell, one of the council's founders, for a story I wrote years ago, I have been diligent about monitoring my Vitamin D levels as well as my husband's (his initial test score was 12, after living in Canada for years; mine was 43, after living in San Diego).

We've not suffered from flus or colds ever since -- and my husband works in a medical hospital where a top challenge is getting physicians to wash their hands (as is true for most hospitals). :-)

Nice blog. Very cute kid!

Gina Pera, author
Is It You, Me, or Adult A.D.D.?

The primary endpoint is barely significant, and this is a fairly small trial. It's promising data, but like you say we need more corroborating data.

This from an online news story about the Vit.D & influenza trial:

"Mitsuyoshi Urashima, the Japanese doctor who led the trial, has told media that vitamin D was more effective than vaccines in preventing flu. Data supporting that comment was not part of the published study. However, antiviral drugs that are highly toxic and too dangerous for children (even though doctors recklessly prescribe them for prevention of the flu) only reduce the chance of getting the flu by 8%. The data shows that a vitamin is highly superior to these drugs at preventing the flu â a fact that will either be ignored by the FDA or cause their Big Pharma stomachs to churn."