Too much vitamin A can actually be harmful. Although it is important to get sufficient vitamin A, you should do this by eating well, not by taking supplements. You should especially avoid megadosing (taking very large doses). In fact, taking more than 2,500 international units (IU) a day increases your risk of cancer and appears to increase your risk of bone fractures. Do not take more than 2,500 IU a day, which is below the standard dosage in many vitamin supplements. In choosing a supplement, try to find one that has less than 2,500 IU of vitamin A and its precursor, beta carotene, combined. While the body will not convert beta carotene into vitamin A if it has no need for it, both substances in excess can increase your risk of cancer.
Why can megadosing be dangerous? Because vitamin A is a nutrient that is "level-sensitive." When vitamin A levels in the body are moderate, it works as an antioxidant and is important to the functioning of your body. Remember we do not know if antioxidants effects are valuable in deceasing aging or age-related disease. However, when you megadose, the surplus vitamin A does the opposite. Rather than functioning as an antioxidant, high doses of vitamin A work to oxidize tissues, cause DNA damage, and deplete your bones of calcium. So, taking too much vitamin A makes you age faster.
A study in Finland showed that people taking vitamin A had a higher risk of lung cancer, atherosclerosis, and, for smokers, stroke. Several other studies have confirmed these findings. Also, excessive amounts of vitamin A may cause liver damage. Smokers need to be especially careful about taking any kind of vitamin A, even the beta carotene form of vitamin A; when combined with smoke, vitamin A and beta carotene can be toxic and can increase rates of cancer.
Too much vitamin A can actually be harmful. Although it is
important to get sufficient vitamin A, you should do this by eating
well, not by taking supplements. You should especially avoid
megadosing (taking very large doses). In fact, taking more... More