Vitamin D is an essential nutrient for maintaining the life of higher animals and belongs to Group A B、C、 The general term for molecules with the same structure as the D ring but different side chains. The structures of the A, B, C, and D rings are derived from the cyclopentadienyl phenanthrene ring structure of steroids. Vitamin D comes in various forms such as D2, D3, D4, D5, D6, and D7 depending on its side chain structure. The only active forms that truly play a role in animal nutrition are D2 (ergocalciferol) and D3 (cholecalciferol).
Vitamin D2, also known as ergocalciferol derived from plants, is named 9,10-broken chain - (5Z, 7E) -5,7,10 (10), 22-gastotenetetraen-3 β - ol. It is a colorless crystal with a melting point of 115-118 ℃, insoluble in water but easily soluble in ethanol and other organic solvents; Vitamin D3 is a cholecalciferol present in animal tissues and fish liver oil, officially named 9,10-broken chain (5Z, 7E) -5,7,10 (19), 22-cholesterol-3 β - ol ergocalciferol. Its precursor is ergosterol from plants, which is a colorless crystal with a melting point of 84-85 ℃ and insoluble in water
Vitamin D3 can promote bone calcification by increasing calcium and phosphorus absorption in the small intestine. Even if the absorption in the small intestine does not increase, it can still promote bone salt deposition, which may be the result of vitamin D3 allowing Ca2+to enter bone tissue through the osteoblast membrane. The deficiency of VD3 can lead to calcium absorption and bone mineralization disorders, causing the occurrence of rickets [7]. Children who lack sunlight for a long time are prone to poor bone growth due to insufficient bone calcification. Simply increasing calcium in food, if vitamin D3 is insufficient, still cannot meet the requirements for bone calcification. But 1,25-dihydroxyvitamin D3 has a dual effect on bone tissue. Biological doses of 1,25-dihydroxyvitamin D3 can enhance osteoblast activity and increase the number of osteoblasts, while exceeding physiological doses can increase osteoclast activity
