Calcium carbonate: It is insoluble in water and needs to be neutralized with gastric acid. It is highly irritating to the stomach, prone to constipation, and has low absorption rate.

Calcium lactate, L-calcium lactate, and calcium gluconate: The calcium content is low. Calcium lactate supplements calcium and brings in lactic acid that causes fatigue; calcium gluconate is not suitable for people with diabetes; the preparations add pigments , fragrance, are particularly harmful to children’s health. But their advantage is: high absorption rate.