As early as the early 1930s, scientists discovered that exposure to sunlight or consumption of olive oil, flaxseed oil, and other UV irradiated foods could combat osteoporosis. Further research by scientists identified and named vitamin D as the active ingredient in the human body for combating osteoporosis.

Vitamin D (VD for short) is a fat soluble vitamin, which is a group of steroid derivatives with anti rickets effects and similar structures. The most important ones are vitamin D3 (cholecalciferol, cholecalciferol) and vitamin D2 (calciferol). Vitamin D in the diet mainly comes from animal based foods such as fish liver, egg yolk, butter, etc. After ingestion, it is absorbed from the small intestine in the presence of bile and transported into the bloodstream in the form of chylomicrons. It is converted into 1,25-dihydroxyvitamin D3 by liver, kidney, and mitochondrial hydroxylase, which has biological activity and can stimulate the synthesis of calcium binding protein (CaBP) in the intestinal mucosa, promote calcium absorption, and promote bone calcification. 7-dehydrocholesterol, a cholesterol derivative in the human body, is stored subcutaneously and can be converted into cholecalciferol under sunlight or ultraviolet radiation. It is an endogenous vitamin D that promotes the absorption of calcium and phosphorus.

VD is a derivative of steroids. It is a white crystal, soluble in fat, with stable properties, high temperature resistance, antioxidant, not resistant to acid and alkali, and can be destroyed by fatty acid decay. Animal liver, fish liver oil, and egg yolk are rich in content. The daily requirement for infants, children, adolescents, pregnant women, and nursing mothers is 400 IU (international units). When lacking, adults are prone to osteomalacia, and children are prone to rickets. If blood calcium decreases, there may be hand and foot twitching, convulsions, etc., which are also related to the development of teeth. Excessive intake of vitamin D can cause high blood calcium, loss of appetite, vomiting, diarrhea, and even ectopic ossification of soft tissues