Quote Originally Posted by manothemoors View Post
The richest source is oily fish, in particular cod liver oil. Dairy products contain smaller amounts. Fortified breakfast cereals contain some, but not nearly enough.
Fish oil derived from the flesh of the fish is much higher in vitamin D than cod liver oil. Cod liver oil also has the disadvantage that it is extremely high in vitamin A, so that if you take too much of it you risk an overdose of that. Too much vitamin A is lethal. Quite a lot of people have died through eating polar bear liver, which is enormously high in vitamin A.