Vitamin D may reduce the incidence of seasonal influenza

Increased intakes of vitamin D may reduce the incidence of seasonal flu, according to a new study.

In the randomized controlled trial, 334 Japanese schoolchildren were randomly divided into two groups: One group received daily supplements of vitamin D3 (1,200 International Units), while the other group received a placebo (1). During the course of four months, the incidence of influenza was 11 percent in the vitamin D3 group, compared with 19 percent in the placebo group.

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 percent 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.

The study suggests that vitamin D3 supplementation during the winter may reduce the incidence of influenza A, especially in schoolchildren, the researchers concluded.

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”.

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.

1. Urashima M. et al. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. American Journal of Clinical Nutrition. 2010.