Vitamin A can be toxic if taken in excessive quantities. Usually if a vitamin is obtained from food,
rather than pills, it can be regarded as safe. However, some foods that contain large quantities of
vitamin A, such as liver from marine or polar animals, can also be potentially toxic.
The body can convert a number of other dietary constituents into vitamin A. These are known as provitamins A and include a number of orange to yellow compounds called carotenes. As long as vitamin A is obtained from food in the provitamin A forms it is not even toxic. So the safest forms of vitamin A are the provitamins A in plants such as green leafy and yellow vegetables.