At present, vitamin D is also considered as a steroid hormone. The main effective component of calcium tablets is calcium.

The importance of calcium in ensuring strong bones and teeth and preventing osteoporosis. Once calcium is insufficient, it will easily lead to tooth decay, osteoporosis and osteomalacia, and children are prone to developmental retardation, low back pain and knee pain.

The most important members of vitamin D family are VD2 (ergocalciferol) and VD3 (cholecalciferol). Vitamin D is a derivative of different provitamins after ultraviolet irradiation. Plants do not contain vitamin D, but both animals and plants contain provitamin.

Vitamin D is a fat-soluble vitamin with five compounds, among which vitamin D2 and vitamin D3 are closely related to health. They have the following three characteristics: they exist in some natural foods; 7- dehydrocholesterol produced by cholesterol is stored under the skin of human body and can be converted into vitamin D3 after ultraviolet irradiation. Proper sunbathing is enough to meet the human body's demand for vitamin D.

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