What are the side effects of vitamin A?

If you take too much vitamin A, it can cause severe side effects. If you have liver disease and or drink a lot of alcohol, vitamin A could damage your liver. Smokers who drink alcohol and take beta-carotene (a form of vitamin A) can have a higher risk of cardiovascular disease and lung cancer.

You should not take vitamin A if you are pregnant unless your doctor tells you to take it. Vitamin A can cause birth defects if taken in large amounts. You may need a special prenatal vitamin created for women who are pregnant. Your dosage may need to be adjusted if you are breastfeeding.

Using preformed vitamin A (such as retinol, which comes from animal sources) has a greater risk of producing side effects than provitamin (such as beta-carotene, which comes from plant sources).

Dr. Michael Roizen, MD
Internal Medicine
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.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.