The friend above is right. The key to calcium supplementation is absorption. If absorbed well, any calcium will do. But it is better for middle-aged and elderly people to eat oyster calcium carbonate. Oyster calcium carbonate contains vitamin D, which can promote the absorption of calcium, so it is easy to absorb. There is a lot of calcium on the market now, which is a mixture of fish and pearls. Be sure to see the ingredients and calcium content clearly!