An Introduction to Vitamin A
Vitamin A is one of the fat-soluble vitamins, and is in fact a group of related compounds including retinol, retinal, retinoic acid and vitamin A precursors called carotenoids.
It carries out numerous important functions in the body, acting as an important antioxidant, contributing to the formation of white blood cells and strengthening the immune system, helping with normal growth and bone development, keeping epithelial cells moist and healthy, and is especially important in the eye where it is needed to form rhodopsin, a molecule which absorbs light and is needed to see in low light conditions, as a result, night blindness is one of the first symptoms of vitamin A deficiency.
Importantly for plant-based people, the retinoids are only found in animal products, therefore our main source of vitamin A is from provitamin A carotenoids such as beta-carotene, alpha-carotene and also beta-cryptoxanthin, which are compounds that can be turned into vitamin A.
Plant sources of carotenoids (and therefore vitamin A) are extremely numerous and getting enough vitamin A is not a problem for us plant-eaters.
Great sources of vitamin A are red bell peppers, sweet potato, carrots, broccoli and spinach among many others, and carotenoids are more easily absorbed from cooked food.
Unfortunately, some populations around the world are still vulnerable to vitamin A deficiency, especially in the developing world, with hundreds of thousands of children becoming blind and suffering developmental problems every year as a result. In these circumstances supplementation is essential.
For those of us who are eating a varied whole-food plant-based diet supplementation is definitely unnecessary and high doses of vitamin A from supplements may even be harmful, interfering with the actions of vitamin D and potentially even causing birth defects.
Interestingly, arctic explorers became sick after eating polar bear liver which is extremely high in retinol, causing a condition known as hypervitaminosis A.
Fortunately for the plant-powered among us, these toxicity problems result only from the intake of retinoids from animal sources or supplements and not from the carotenoids that we find in our plant foods. Yet another reason to stick to plants!