Cod liver oil is suitable for what age group? Cod liver oil is a nutritional supplement rich in vitamins A and D. It is most suitable for children over 3 years old, the elderly, and people who are deficient in vitamins A and D. Because these people are often deficient in vitamins A and D, cod liver oil can help them supplement these vitamins. Effects of children eating cod liver oil 1. Help children supplement nutrition: Cod liver oil is rich in vitamins A and D, which helps children’s growth and development. 2. Enhance immunity: Vitamin A in cod liver oil can strengthen the immune system