What is the potential importance of taking vitamin D?

Vitamin D can be obtained from the diet or from sunlight exposure, but these sources can be insufficient, especially in older people and vegans during the winter months. In healthy adult Western European populations, 6 to 14% percent have been reported to be vitamin D deficient, but good data are not available for the US. Vitamin D insufficiency is associated with bone loss and fractures in older people. Reduced bone loss from vitamin D supplements has been reported in some,though not all, studies. In one double-blind study, supplementation with 800 IU per day of vitamin D prevented bone loss more effectively than 200 IU per day in postmenopausal women. In addition, vitamin D supplementation has been shown to reduce the risk of falls in older people. While vitamin D is known to be toxic in very high amounts, up to 2000 IU per day is considered safe.