Epidemic influenza and vitamin D

In 1981, R. Edgar Hope-Simpson proposed that a ‘seasonal stimulus’ intimately associated with solar radiation explained the remarkable seasonality of epidemic influenza. Solar radiation triggers robust seasonal vitamin D production in the skin; vitamin D deficiency is common in the winter, and activated vitamin D, 1,25(OH) 2 D, a steroid hormone, has profound effects on human immunity. 1,25(OH) 2 D acts as an immune system modulator, preventing...