Vitamin D as effective as vaccine in preventing flu

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Taking high doses of vitamin D3 supplements in winter helps reduce risk of acquiring seasonal flu in winter, a new Japanese trial demonstrated.

The trial results, reported in the March 10, 2010 issue of American Journal of Clinical Nutrition, show that children given vitamin D(3) supplement were 42 percent less likely to get infected with seasonal flu than those who were given a placebo.

The efficacy is remarkable as it may be comparable to that of flu vaccine, which is generally low because the virus used to construct the vaccine is likely different from the circulating one.

Deficiency of Vitamin D, which is synthesized after human skin is exposed to sunlight or UV rays, has been associated with increased risk of seasonal flu and swine flu as well.  However, most of such studies were epidemiological or observational.

In the randomized, double-blind, placebo-controlled trial, Dr. Mitsuyoshi Urashima and colleagues at Division of Molecular Epidemiology Jikei University School of Medicine Minato-ku in Tokyo Japan gave one group of schoolchildren 1,200 international units per day of vitamin D(3) and another group a placebo to see how vitamin D would prevent seasonal flu.

The primary outcome of the trial was the incidence of influenza A and diagnosis was established by testing a flu antigen in a nasopharyngeal swab specimen.

During the trial between Dec 2008 and March 2009, 18 of 167 (10.8%) children given vitamin D tested positive for flu infection compared to 31 of 167 (18.6) children in the placebo group.  The relative risk is 0.58, meaning those taking vitamin D were at 42 percent reduced risk of seasonal flu.

The anti-flu effect was found much more significant among children who had not been taking other vitamin D supplements and who started nursery school after age 3.  The reduction in the risk was 64 percent for both groups.

In a subgroup of children who were previously diagnosed with asthma, 2 children taking vitamin D supplements experienced asthma attacks while 12 children receiving placebo suffered asthma attacks - meaning that vitamin D cut the risk by 83 percent.

The researchers concluded that the results suggest that vitamin D3 supplementation during the winter time may reduce the incidence of influenza A.

Dr. John Cannell, one of most knowledgeable vitamin D experts in the world and director of Vitamin D Council, a non-profit organization, and colleagues earlier published a heavy-weight review article in a scientific journal called Virology explaining that vitamin D is needed for the production of antibacterial peptides which help prevent flu. 

In winter, people tend to stay indoors.  Those who lack exposure to sunshine are prone to becoming vitamin D deficient. This is why people in winter are at higher risk of influenza including seasonal flu.

Dr. Cannell suggests adults can take 5,000 IU per day and try to maintain a blood level of 50 to 80 ng/mL (or 125 to 200 nm/L) year-round.  One early study suggests that it is safe for schoolchildren to take 2,000 IU per day for a year without any noticeable side effects.

Vitamin D is found only in a few foods including eggs and fatty fish like salmon.  Because of this, the vitamin D is fortified in some foods like milk, orange juice and cereals.  But vitamin D levels in such foods are fairly low and you may have to drink literally 20 glasses of milk to get enough vitamin D.  Vitamin D supplements are a good source of the nutrient even though sunshine is the best.

Dr. Cannell cautions that high intake of vitamin A can reduce the efficacy of vitamin D.  Cod liver oil, high in vitamin A while relatively low in vitamin D, is not as good as it used to be as a vitamin D source.

A health observer suggests that regardless of your vaccination status, an adequate level of serum vitamin D should be maintained to prevent flu and many other serious diseases like cancer, heart disease and diabetes..

For more detailed information on vitamin D, visit Vitamin D Council.

By David Liu and editing by Denise Reynolds

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