Today, typical calcium deficiencies like rickets, chicken chest, and hunchback are rare. However, mild calcium deficiency is still a prominent problem in children and adolescents. Mild calcium deficiency or the early stage of calcium deficiency is mainly manifested by psycho-neurological symptoms, such as irritability and abrasiveness, disobedience and crying, strange temper; restless sleep, such as not easy to fall asleep, night terrors; sweating a lot, sweating even when it should not. In fact, many of the symptoms of calcium deficiency are very atypical, they are just risk factors for the occurrence of a certain symptom such as dental caries, or even a decrease in immunity, resistance, easy to catch a cold, fever, diarrhea, etc., which may all be related to calcium deficiency. 5 factors affect calcium absorption: 1. Age, children and adolescents in the growth period have strong calcium absorption ability, and the absorption rate of calcium decreases when they grow older. Infants and young children can be as high as 50% to 60%, children and adolescents 30% to 40%, adults 20% to 30%, middle-aged people 10% to 20%, more than 60 years of age less than 10%. Therefore, the intake of sufficient calcium from a young age is of profound significance to the quality of bones in old age. 2, vitamin D can promote the absorption of calcium, maintain the ratio of calcium and phosphorus in the blood, so that calcium is deposited in the bones, so while supplementing calcium, vitamin D must be involved in order for calcium to be absorbed and utilized. The most important factor affecting calcium absorption is vitamin D. To be exact, it is the active vitamin D in the body. This active vitamin D is produced by the vitamin D in food and 7-dehydrocholesterol in human skin after sunlight exposure and then synthesized into vitamin D3, and then in the liver, especially the kidney, by hydroxylation reaction. It promotes the absorption of calcium in the small intestine and even in the colon. If the body is deficient in active vitamin D, the absorption of calcium is only 10%. If vitamin D is supplemented and active vitamin D is synthesized in the liver and kidneys, calcium absorption will increase to about 60% in cases of severe calcium deficiency. 3, high-fat diet or poor absorption of fat will cause calcium to combine with fatty acids to form insoluble calcium soap and affect absorption. 4, diarrhea and other digestive tract diseases resulting in malabsorption as well as tension, depression, resentment and other emotional states will also affect the absorption of calcium. 5, the consumption of vegetables containing high oxalic acid, such as wild rice, bamboo shoots, spinach, amaranth, can make calcium become insoluble calcium oxalate and not easily absorbed. If cooked in hot water for one minute before putting in the pot, it can remove most of the oxalic acid in the vegetables. The amount of calcium supplementation varies from person to person, roughly calculated, health care calcium supplementation for: infants and children can supplement 200-300 mg per day, school-age children 300-400 mg, 500-600 mg for adolescents. According to incomplete statistics, there are nearly 200 kinds of calcium supplement products on the domestic market, but there are only about ten kinds of calcium sources, such as calcium carbonate, calcium oxide, calcium gluconate, calcium citrate (calcium citrate), calcium lactate, calcium hydroxyphosphate and various kinds of calcium amino acids. When choosing calcium supplements, the first thing to consider is the calcium content, followed by the calcium solubility and absorption, and again, the price and taste. The ideal calcium supplements should not only have high calcium content, good solubility and high release rate in gastric juice, good absorption rate, no side effects, easy to take, good taste, etc., but also contain a variety of amino acids, vitamins and trace elements needed by the human body, so that it can achieve both calcium and promote the absorption of calcium. Tips: Calcium supplementation, too much is too little. Although calcium is an essential element for the human body, but it is not a complete pill, calcium supplement is not more than good. Scientific experiments have proven that too much calcium can easily cause constipation. Some preparations containing only calcium, if the dosage is too much, can lead to a lack of phosphorus in the body. Phosphorus is closely related to nerve tissue, and at the same time, it causes bone softening. Therefore, it is important not to blindly overdose when giving calcium to children.