The side effects of excessive intake of vitamin D may lead to hypervitaminosis D, even poisoning, manifesting as headache, anorexia, increased serum calcium and phosphorus, calcification of soft tissue, renal failure, hypertension and other symptoms. Excessive intake of vitamin D by babies may affect the development of intelligence and lead to ossification of the bones.
Vitamin D (abbreviated as VD) is a fat-soluble vitamin, a kind of cyclopentane polyhydrogenated phenanthrene compound. It is a group of vitamins structurally related to sterols and functionally prevents rickets. The most important ones are vitamin D3 and D2. The former is formed by ultraviolet irradiation of 7-dehydrocholesterol under human skin. The latter is formed by ultraviolet irradiation of ergosterol contained in plants or yeast. The main function of vitamin D is to promote the absorption of calcium and phosphorus by intestinal mucosal cells. Calcium ion absorption in the intestine requires a calcium-binding protein, and 1,25-dihydroxyvitamin D3 can induce the synthesis of this protein, promote Ca2+ absorption, and also promote the renewal of calcium salts and the formation of new bones. It also promotes phosphorus absorption and the reabsorption of calcium and phosphorus by renal tubular cells, thus increasing the concentrations of blood calcium and phosphorus, which is beneficial to the formation and calcification of new bones. In addition, vitamin D also promotes the growth, differentiation, and immune regulation of skin cells. Generally, adults who are frequently exposed to sunlight are unlikely to suffer from vitamin D deficiency. Infants, pregnant women, lactating mothers, and elderly people who do not often go outdoors should increase their vitamin D intake to 10 μg (equivalent to 400 international units) per day. Children who lack vitamin D may suffer from rickets, and adults may suffer from osteomalacia. Food sources of vitamin D are relatively abundant in high-fat seafish, animal liver, egg yolk, and cream, with high content in cod liver oil.
