People who take multivitamins, cod liver oil or supplements are being warned to check how much vitamin A they are taking, as too much can trigger hair loss. Some people may be doubling up on products without realising they are stacking the same vitamin from several sources. Vitamin A, also known as retinol, is needed for the immune system, vision in dim light and healthy skin. It is found in foods including cheese, eggs, oily fish, milk, yoghurt and liver.