Sunlight, Vitamin D and allergy

Vitamin D is well known for its role in bone metabolism but it also has an important role in modulation of the immune response. Vitamin D (Vit D) results from the conversion of Vitamin D3 at the level of the skin after exposure to ultraviolet (UBV) light or following the ingestion of Vitamin D2 or D3. At extreme latitudes, the intensity of the UBV in winter is not strong enough to synthesize enough Vit D, which can lead to Vit D deficiency with skeletal or extra-skeletal signs. Among the extra-skeletal manifestations, which can be associated with the immune system, are certain autoimmune diseases, such as type 1 diabetes, multiple sclerosis and allergies. Concerning allergies, in particular an increase in food allergies and/or anaphylaxis; asthma and atopic dermatitis might be included. Here we discuss observations collected from asthmatic patients; many of them allude to a Vit D deficiency while a smaller number report possible aggravation of their allergic symptoms after taking Vit D. This latter possibility explains the cautious attitude of physicians vis-a-vis Vit D supplementation, and when this is considered, they choose to recommend increased natural light exposure. (C) 2016 Elsevier Masson SAS. All rights reserved.