? Calcium in food needs to undergo a complicated process of digestion and absorption in human body before it can truly become a part of human body and play its important physiological role. There are two main ways of absorption:
1. intracellular transport pathway
Calcium ions are first swallowed by epithelial cells on one side of the intestine to form vesicles, then slowly spread to the other side of the cell membrane, and finally actively transported to the blood circulation through the calcium pump. This transport does not require the participation of vitamin D, but the absorption is very slow. The other way is to open the channel of calcium ion on intestinal cell membrane in a few seconds under the action of vitamin D, so that a large number of calcium ions can quickly cross the cell membrane and enter the human cytosol. At the same time, active vitamin D promotes calcium ions to enter the cells by binding with calcium-binding protein on the cell membrane of intestinal mucosa, and then discharges calcium ions from the cells into the blood through the action of calcium pump. This process requires a certain amount of energy, so it becomes active absorption.
2. Cell bypass pathway
When the concentration of calcium ion in intestinal cavity is high, a part of calcium ion can directly diffuse into blood along the concentration gradient through cell bypass. Vitamin d can also promote this process. This form of absorption does not consume energy, but the absorbed calcium only accounts for a very small part of the total, which is often ignored. The absorption of calcium by human intestine is limited. When the daily calcium intake of normal people is in the range of 5 ~ 10 mg/kg body weight, the absorption increases with the increase of calcium intake, and the calcium ion absorbed by the intestine increases linearly. However, when the calcium intake is above 10 mg/kg body weight, it is saturated by active absorption through intracellular transport. At this time, increasing calcium intake will not significantly increase the amount of calcium absorbed by the intestine.
? So eating egg skin powder to supplement calcium is just one way. There is no science or not. In our food, a normal diet can actually ensure calcium intake. We know the absorption process of calcium by human body, so we should pay attention to how to increase the absorption of calcium by human body, rather than what is beneficial to eat.
? Here are some precautions for you.
? (1) Vitamin D can promote intestinal absorption of calcium and phosphorus. When adults take vitamin D 100 ~ 200 international units orally every day, the absorption of calcium increases obviously. Foods rich in vitamin D include cod liver oil, egg yolk, cream, pig liver, milk and so on. While plant food contains almost no vitamin D, human skin contains 7- dehydrocholesterol, which is converted into vitamin D after being irradiated by ultraviolet rays or sunlight. Therefore, children often bask in the sun, which is conducive to promoting bone development.
? (2) Lactose can promote the absorption of calcium. Because lactose and calcium form low molecular weight soluble compounds and promote the absorption of calcium, lactose can accelerate the absorption of calcium by small intestine.
? (3) Adequate protein supply in diet is beneficial to calcium absorption. Amino acids decomposed by protein, especially lysine and arginine, form soluble calcium salts with calcium, which is beneficial to the absorption of calcium. It was observed in adults that a constant amount of calcium was provided under the conditions of different protein supply, and the observation period of a certain dose was 15 days. It is found that increasing the supply of protein can obviously increase the absorption of calcium.
? (4) Appropriate ratio of calcium to phosphorus can promote calcium absorption. It is generally believed that the ratio of calcium to phosphorus is 2: 1, which is beneficial to the absorption of calcium. Some nutritionists recommend that the ratio of calcium and phosphorus in infancy is 1.5: 1, and one year later it is 1: 1. Animal experiments show that when the ratio of calcium to phosphorus is lower than 1∶2, the dissolution and detachment of calcium from bone increase, which may lead to osteoporosis in severe cases.
? (5) Lysine, arginine and tryptamine can increase calcium absorption, especially lysine. Amino acids can form easily absorbed calcium salts with calcium, so a proper amount of protein in diet can increase the absorption rate of calcium in small intestine, but excessive intake of protein can also increase urinary calcium excretion, resulting in a negative calcium balance. When the daily intake of protein is in the range of 47 ~ 93g, a positive calcium balance can be maintained, that is, calcium remains in the body. ?
(6) Phytic acid, cellulose, uronic acid, sodium alginate and oxalic acid can reduce the absorption of calcium. They all exist in common foods and can form salts with calcium that are not easily absorbed. Calcium can only be absorbed by human body unless it is destroyed by enzymatic hydrolysis. Some people think that rye contains more phytase, which can destroy the combination of phytic acid and calcium. For this reason, some people advocate adding rye to pasta. Calcium in foods containing more oxalic acid, such as spinach, water spinach, taro stalks, thick-skinned leaves, amaranth and cut roots, is difficult to be absorbed, which affects the absorption of calcium in other foods by gastrointestinal tract. The theoretical value of available calcium is -30 ~-384, so we should pay attention to the content of phytic acid and oxalic acid when choosing calcium-supplemented food.
? (7) Excessive fat intake or fat malabsorption can lead to excessive free fatty acids, which combine with calcium to form insoluble calcium soap, which is discharged from feces. The longer the fatty acid carbon chain, the higher the saturation and the lower the utilization rate of calcium. Medium chain fatty acids can improve the absorption of fat and calcium.
? (8) Excessive alcohol and nicotine will affect the absorption of calcium, so drink less and smoke less.
? (9) Acidic medium is beneficial to the absorption of calcium, and it can keep the dissolved state of calcium because of its low PH value. Most calcium is absorbed in acidic environment before the upper part of small intestine.
? (10) Exercise can increase calcium absorption. When there is no exercise, the absorption and utilization of calcium decrease.
? (1 1) hormones play an important role in calcium absorption. When blood calcium decreases, parathyroid hormone secretion increases, which stimulates the synthesis of 1.25- dihydroxy vitamin D3, promotes the absorption of calcium in intestine and the release of calcium in bone. On the contrary, when blood calcium increases, calcitonin secretion increases, which promotes calcium in blood to enter bones. Thyroid hormone, adrenocortical hormone and the like are not conducive to the absorption of calcium.