Like HowStuffWorks on Facebook!

Vitamin A Supplements

How much is enough? For general health, limit vitamin A supplementation to 5,000 IU (1,000 RE) for men and 2,500 IU (500 RE) for women. A high dose of up to 50,000 IU (10,000 RE) for one or two days only to treat a viral infection is acceptable. Pregnant women should use carotenes instead.

When shopping for carotene supplements, look for "mixed carotenoids" so that you get some of the other helpful carotenes besides just beta-carotene. The best source of these supplements is palm oil. You don't need to worry about fat intake, because the carotenes are extracted from the palm oil. Carotenes from the algae D. salina are second best. Avoid synthetic preparations. A daily amount of 25,000 IU is recommended for general health purposes.

Don't overdo it. Large amounts of vitamin A are clearly toxic. One massive dose or large doses taken over an extended period of time can cause hair loss, joint pain, nausea, bone and muscle soreness, headaches, dry and flaky skin, diarrhea, rashes, enlarged liver and spleen, cessation of menstruation, and stunted growth.

Two recent studies indicate that toxicity can occur at levels far lower than previously thought. Researchers report that daily doses exceeding 25,000 IU over a period of time have caused lasting liver damage. And a recent study of pregnant women found a fivefold increase in the risk of having a baby with a birth defect for women taking more than 10,000 IU compared with those getting less than 5,000 IU.

Excessive intake of retinol can be detrimental to your health, specifically your heart and bone health. One clinical trial showed that people who took 25,000 IU of vitamin A per day for 3-4 years saw their triglycerides and total cholesterol increase while their good cholesterol (HDL) decreased. Both animal and human studies show that excessive vitamin A intake can accelerate bone loss and inhibit formation of new bone, increasing the risk of osteoporosis. In humans, small studies have found these effects at about 85,000-125,000 IU per day. Therefore you should limit retinol supplementation to 500-600 RE per day if you are at risk for either cardiovascular disease or osteoporosis. In other words, limit intake if you plan to live past age 50!

In a few reported instances, vitamin A toxicity has occurred after eating large amounts of liver. (Polar bear liver is especially high in vitamin A; it contains as much as 560,000 IU (169,697 RE) per ounce!) Because the liver stores vitamin A, eating large amounts daily is not wise.

This information is solely for informational purposes. IT IS NOT INTENDED TO PROVIDE MEDICAL ADVICE. Neither the Editors of Consumer Guide (R), Publications International, Ltd., the author nor publisher take responsibility for any possible consequences from any treatment, procedure, exercise, dietary modification, action or application of medication which results from reading or following the information contained in this information. The publication of this information does not constitute the practice of medicine, and this information does not replace the advice of your physician or other health care provider. Before undertaking any course of treatment, the reader must seek the advice of their physician or other health care provider.