Lee Swanson Research Update

Vitamin D Shows Promise Against Seasonal Flu

April 2010

Increased intakes of vitamin D may reduce the incidence of seasonal flu. That’s what a randomized, double-blind, placebo-controlled trial from Japan shows.

While the link between vitamin D and colds and flu is not new, researchers led by Mitsuyoshi Urashima from Jikei University School of Medicine state that until now, this has not been tested in rigorous clinical trials.

Writing in the American Journal of Clinical Nutrition, the Japanese researchers report that daily supplements of vitamin D-3 reduced the influence of seasonal flu (influenza A) by over 40%.

Vitamin D’s role in immune health is well reported and was the subject of a positive opinion from the European Food Safety Authority’s Panel on Dietetic Products, Nutrition and Allergies.

The panel concluded that "a cause-and-effect relationship has been established between the dietary intake of vitamin D and contribution to the normal function of the immune system and healthy inflammatory response, and maintenance of normal muscle function."

In the current study, 334 schoolchildren were recruited to participate in the study, and the children were randomly divided into two groups: One group received daily supplements of vitamin D-3 (1,200 IU), while the other group received placebo. The diagnosis of influenza was performed by trained physicians.

During the course of four months (December 2008 to March 2009), the incidence of flu was 11% in the vitamin D-3 group, compared with 19% in the placebo group, the researchers said.

The benefits of vitamin D supplementation were even more noticeable in children who had low levels of vitamin D at the start of the study, with a 74% reduction in the incidence of flu observed.

The researchers also noted benefits beyond flu, with asthma attacks significantly reduced in asthmatic children in the vitamin D group, compared with asthmatic children in the placebo group.

"This study suggests that vitamin D-3 supplementation during the winter may reduce the incidence of influenza A, especially in specific subgroups of schoolchildren," Urashima and co-workers wrote.

American Journal of Clinical Nutrition Published online ahead of print.

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