[Human anti-infectious defence may be enhanced by vitamin D]

Findings about the significance of vitamin D for intrinsic immune defense may explain the effects of sunlight on immunity. Beyond the skin and the mucus layer of mucosae, antimicrobial peptides constitute the first-line defence, acting very rapidly. Their synthesis is dependent on vitamin D. Certain antimicrobial peptides inhibit the function of influenza virus. The most important factor affecting vitamin D production is sunlight, whereby the levels of this vitamin exhibit seasonal variation. Risk groups should pay special attention to the supply of vitamin D particularly during the winter infection season.