The main function of vitamin
D is to allow a better intestinal absorption of calcium and to integrate it into the bones to strengthen them. Vitamin D is obtained both by diet, and by exposure to natural sunlight. A significant lack or deficiency
of vitamin D, thus has a major impact on adults, including weakened, brittle bones. In children, this can lead to rickets, a condition that has become rare in industrialized countries, but still possible in poor countries, causing impaired growth and bone deformities. Vitamin D is also produced naturally by the skin under the effects of the sun, its deficiency can also result in particular in elderly and sedentary people, who have insufficient sun exposure. Vitamin D supplements are frequently available in vials for drinking for small children as well as the elderly.