Increased intakes of vitamin D may reduce the incidence of seasonal ‘flu, according to results of a randomized, double-blind, placebo-controlled trial from Japan.
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 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 D3 reduced the influence of seasonal ‘flu (influenza A) by over 40 per cent.
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 (EFSA) Panel on Dietetic Products, Nutrition and Allergies (NDA).
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”.
Indeed, only recently Danish scientists reported that vitamin D is necessary to trigger T cells – the immune system’s killer cells – into action, and insufficient levels of the vitamin mean the cells remain dormant and inactive (Nature Immunology, doi: 10.1038/ni.1851).
Three hundred and thirty four schoolchildren were recruited to participate in the study, and the children were randomly divided into two groups: One group received daily supplements of vitamin D3 (1200 International Units), while the other group received placebo. The diagnosis of influenza was performed by trained physicians.
During the course of four months (December 2008 until March 2009), the incidence of ‘flu was 11 per cent in the vitamin D3 group, compared with 19 per cent in the placebo group, said the researchers.
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 per cent 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 D3 supplementation during the winter may reduce the incidence of influenza A, especially in specific subgroups of schoolchildren,” wrote Urashima and co-workers.
Canada’s Public Health Agency of Canada (PHAC) confirmed last year that it would investigate the role of vitamin D in protection against swine flu.
The agency started a study in 2008 on the role of vitamin D in severe seasonal influenza, which it said it will adapt to the H1N1 swine flu virus.
“Researchers in PHAC are working with colleagues at McMaster University and with partners at other universities and hospitals to determine whether there is a correlation between severe disease and low vitamin D levels and/or a person's genetic make up. This line of research in seasonal influenza will be adapted to H1N1,” wrote the agency in an e-mail to our sister site, NutraIngredients-USA.com.
Source: American Journal of Clinical Nutrition
Published online ahead of print, doi:10.3945/ajcn.2009.29094
“Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren”
Authors: M. Urashima, T. Segawa, M. Okazaki, M. Kurihara, Y. Wada, H. Ida