The main difference between vitamin D3 and cod liver oil is the difference in the composition of the vitamins contained. Vitamin D3 is one of the D vitamins and is a fat-soluble vitamin. Vitamin D3 can promote intestinal absorption of calcium, promote bone mineralization, promote the formation of bone trabeculae and strengthen bones, and is often used clinically to treat and prevent diseases such as osteoporosis and rickets, which are caused by various causes of vitamin D3 deficiency. Cod liver oil contains vitamin D as well as vitamin A. In addition to the role of vitamin D supplementation, cod liver oil also has a protective effect on the skin and eyesight due to the vitamin A in its composition, but vitamin A is prone to accumulation of toxicity causing damage to liver function.