Vitamin D is a fat-soluble vitamin that is synthesized in the deeper layers of the epidermis of the human skin when exposed to ultraviolet (UV-B) sunlight. Vitamin D is also available from foods of plant and animal origin, but these foods do not contain high levels of this vitamin. The most abundant sources of vitamin D are found in oily fish (salmon, herring, eel), egg yolk, liver, butter and cheese. The amount of vitamin D produced in the skin is not always sufficient, even in summer, and more than 80 % of the population in our latitudes does not get enough during the cold season. It is important to ensure that this important vitamin is not deficient, as vitamin D has many functions in the body.
- The main well-known function of vitamin D is to help maintain the proper concentration and absorption of calcium and phosphorus in the body. This vitamin is essential for the normal development and growth of bones and teeth.
- Vitamin D is important for the immune system. Many immune cells (peripheral mononuclear cells, T lymphocytes of the first and second type (Th1, Th2), B lymphocytes) have been shown to have receptors for vitamin D. This vitamin is involved in the normal functioning of the immune system.
- The analysis of the research data concluded that vitamin D supplementation with 400-1000 IU/day for up to 12 months is safe and helps to support the upper respiratory tract immune system.