Vitamin D and living in northern latitudes--an endemic risk area for vitamin D deficiency.

OBJECTIVES: To review the current literature on the health effects of vitamin D, especially the effects on inhabitants living in the northern latitudes. STUDY
DESIGN: Literature review.
METHODS: The scientific literature concerning health effects of vitamin D was reviewed and the current dietary recommendations for inhabitants living in northern latitudes were discussed.
RESULTS: Vitamin D is a steroid-structured hormone produced in the skin upon exposure to UVB-radiation or obtained from certain food products (for example, liver). Its production is mediated by the vitamin D receptor, which belongs to the nuclear receptor family, and exerts its function as a transcription factor regulating several target genes. Active metabolites of vitamin D play an important role in calcium and phosphate homeostasis. Deficiency of vitamin D results in diminished bone mineralization and an increased risk of fractures. In addition, vitamin D is connected to a variety of other diseases that include different cancer types, muscular weakness, hypertension, autoimmune diseases, multiple sclerosis, type 1 diabetes, schizophrenia and depression.
CONCLUSIONS: Vitamin D plays a fundamental role in calcium and phosphate homeostasis. A deficiency of vitamin D has been attributed to several diseases. Since its production in the skin depends on exposure to UVB-radiation via the sunlight, the level of vitamin D is of crucial importance for the health of inhabitants who live in the Nordic latitudes where there is diminished exposure to sunlight during the winter season. Therefore, fortification or supplementation of vitamin D is necessary for most of the people living in the northern latitudes during the winter season to maintain adequate levels of circulating 25(OH)D3 to maintain optimal body function and prevent diseases.