Calcium carbonate D3, a calcium supplement, is recommended to be taken before meals. Because the concentration of stomach acid is higher when you take it before meals, under the condition of high concentration of stomach acid, calcium becomes free calcium relatively more, and this free calcium is absorbed best. Moreover, vitamin D3 is a fat-soluble vitamin, which can be combined with the fat of food, and the absorption effect will be better. When taking vitamin D3 you should be careful to avoid alcohol and coffee drinks, which can affect the absorption of calcium, and eating a lot of food containing fiber can also affect the absorption of calcium. Calcium carbonate D3 is not recommended to be taken with milk, which may lead to the occurrence of milk-alkaline syndrome, manifested as hypercalcemia, alkalosis and renal insufficiency. In patients with kidney stones it is important to control the total amount of calcium, which usually does not increase the risk of urinary stones when not exceeding 800-1000 mg of elemental calcium per day.