[Adequate level of vitamin D is essential for maintaining good health].

The high prevalence of vitamin D deficiency and insufficiency in the human population results from its inadequate cutaneous production and low dietary intake. Vitamin D status in the organism is determined by circulating levels of 25-hydroxycholecalciferol [25(OH)D3]. 25(OH)D3 is metabolized by a renal 25-hydroxyvitamin D-1alpha-hydroxylase (CYP27B1) into the vitamin D hormone 1,25 dihydroxycholecalciferol (calcitriol), which generates a wide range of biological responses via both the regulation of gene transcription and nongenomic pathways. Most of the circulating metabolite originates from cholecalciferol, which is synthesized in the skin upon exposure to the UVB spectrum of sunlight. The dietary source of vitamin D is extraordinarily low (10%) compared with endogenous production (90%). Recent epidemiological data demonstrated a strong association between poor vitamin D status (i.e. serum 25(OH)D3 levels below 50 nmol/l) and increased risk for chronic illnesses of various etiology. It is now recognized that maintaining a serum 25(OH)D3 level of 80 nmol/l (32 ng/ml) or greater is beneficial in the prevention of osteoporosis, cardiovascular diseases, certain autoimmune diseases, and some forms of cancer. It seems that sensible sun exposure and the use of supplements are the most effective ways of preventing vitamin D deficiency. The aim of the present article is to review new developments related to vitamin D deficiency and insufficiency and their consequences.