In the strictest sense, cod liver oil is not a calcium supplement, but is rich in vitamin A and vitamin D. Vitamin A is mainly used to treat eye diseases, especially those caused by vitamin A deficiency, such as dry eyes, which can be treated through the intake of cod liver oil. The other component of cod liver oil is vitamin D. The role of vitamin D is to promote the absorption of calcium and phosphorus in the mucous membrane cells of the small intestine, although it can promote the absorption of calcium, but it does not mean that cod liver oil is a calcium supplement, because cod liver oil does not contain calcium ions, and the intake of cod liver oil will not increase the content of calcium ions in the blood, so cod liver oil is not a calcium supplement.