Diet, sun, and lifestyle as determinants of vitamin D status

Vitamin D status can be assessed by measuring concentrations of 25-hydroxyvitamin D (25(OH)D). Sunlight is the most important source of vitamin D and stimulates the production of vitamin D-3 in the skin during the summer, depending on age, skin pigmentation, clothing style, and sunscreen use. Seasonal variation in serum 25(OH)D is between 10 and 20 nmol/L in adults and almost absent in nursing home residents. Sunscreen use decreases, but does not abolish, vitamin D production in the skin. Clothing style has a large influence on vitamin D production. Furthermore, vitamin D status can be improved by ingestion of fatty fish and the fortification of milk or orange juice. A high dietary calcium intake has a vitamin D-sparing effect, because it increases the half-life of 25(OH)D. A combination of sunlight exposure, nutrition, food fortification, and supplements is desirable to obtain sufficient vitamin D status in the population of most countries throughout the year.