Because the dietary characteristics of Chinese residents are mainly plant-based food, and the proportion of milk and dairy products is very small, which makes the calcium in the diet more difficult to be absorbed and utilized, so it is more likely to cause calcium deficiency. There are many factors affecting the absorption and utilization of calcium in the diet.
Factors promoting calcium absorption:
1. Vitamin D can increase the active absorption of calcium by increasing the synthesis of specific calcium-binding protein in intestinal epithelial cells.
2. According to the study of calcium balance of newborns, the absorption rate of calcium in breast milk is higher than that in cow milk, which is 25% – 66% and 5% – 38%, respectively.
3. Lactose fermentation results in a decrease in pH or lactose hydrolysate can promote the absorption of calcium. Protein in milk and dairy products can increase calcium absorption.
4. Generally, the absorption of calcium increases when the protein intake goes from the lack to the appropriate level, but when the protein intake exceeds the recommended supply, there is no further impact.
5. In the normal calcium intake, phosphorus has no significant effect on calcium absorption and retention, unless there are too much phytate and calcium forming a complex to inhibit calcium absorption. Long term intake of excessive phosphorus, 1.0-1.5g per day (molar ratio of calcium to phosphorus < 1:3), can damage the balance mechanism, change calcium metabolism, cause hypocalcemia and secondary hyperparathyroidism. In 1989, the ideal ratio of calcium to phosphorus recommended by the United States was 1:1, but the actual ratio of calcium to phosphorus was 1:1.6 for men and 1:1.6 for women, which was not conducive to the absorption of calcium.
6. The absorption rate of calcium in infants and children is higher than that in adults, that in low birth weight infants is higher than that in normal infants, and that in preterm infants is higher than that in term infants. In the period of bone growth, the absorption rate of calcium is as high as 75% in children and 20% – 40% in adults. The secretion of gastric acid and bile contributes to the dissolution and absorption of calcium salts.
Factors that inhibit calcium absorption:
The factors that inhibit calcium absorption include oxalic acid, phytic acid, fatty acid and sodium salt in food. Oxalic acid can form insoluble calcium salt with calcium in food and inhibit calcium absorption. Because vegetable contains more phytic acid, the bioavailability of calcium in the vegetable is very low. When milk and amaranth were eaten at the same time, the calcium absorption rate decreased. Some people compared the absorption rate of calcium in spinach and milk of healthy adults. Milk was significantly higher than spinach, 27.6% and 5.1% respectively. Although phytic acid can inhibit the absorption of calcium, because phytic acid can be hydrolyzed by phytase in the intestine, the effect of phytic acid on calcium utilization is important unless the intake of calcium is very low. Fatty acids (especially saturated fatty acids) can form insoluble soap with calcium in the gastrointestinal tract, reducing the absorption rate of calcium. In girls aged 8-13, high sodium intake reduced calcium retention in bone, accompanied by a decrease in bone mineral density.
