& Joannie Dobbs Saturday
June 30, 2007
Too much Vitamin A can be toxic
MORE THAN 150 years ago, blindness and eye disease in Africa was thought to be due to a dietary deficiency. About 60 years later, vitamin A was found to be the deficient component.
Even now, an estimated half-million children worldwide annually suffer from vitamin A deficiency. This not only causes serious eye problems, but also death from common illnesses like measles due to impaired immune functions.
Question: What does vitamin A do in the body?
Answer: In addition to eye health, vitamin A is needed for normal growth, reproduction, bone health, blood cell production, skin health and immune function. The carotenoid forms of vitamin A also function as antioxidants.
Q: What foods provide vitamin A?
A: In ancient Greece, Hippocrates found that eating liver successfully treated night-blindness. This worked because liver is extremely high in the most active form of vitamin A called retinol. Another form of vitamin A, sometimes called provitamin A, is found in a variety of fruits and vegetables that are yellow, orange or green. Provitamin A is composed of specific types of carotenoids like beta-carotene. This is the compound that gives carrots their characteristic orange color and can be converted into retinol in the body.
Q: How much vitamin A does the body need?
A: Daily needs are less than one milligram of retinol per day. This tiny amount is present in a fourth of an ounce of beef liver (about 2 teaspoons). To meet daily vitamin A needs with plant food sources, the average person needs to eat one of the following: 1/2 cup of sweet potato or baby carrots, a large mango or papaya, one cup of cooked spinach or chopped red bell pepper, or a fourth of an average cantaloupe.
Q: Can you consume too much vitamin A?
A: Yes. Vitamin A (especially the retinol or retinyl forms) is one of the most toxic vitamins. Ongoing consumption of two to three times the current recommended intake of vitamin A in the retinol or retinyl form is associated with increased bone loss and bone-fracture risk as people age. Also, there is evidence that pregnant women may increase the risk of birth defects in their offspring by consuming too much vitamin A during pregnancy.
Q: Are dietary supplements with vitamin A safe to take?
A: It depends on the amount of vitamin A in a person's diet and how everything adds up. Just remember that due to outdated labeling regulations, if a supplement label indicates 100% of the "Daily Value" for vitamin A, it contains about double the current recommended intake (RDA) of vitamin A for adults.
Alan Titchenal, Ph.D., C.N.S. and Joannie Dobbs, Ph.D., C.N.S.
are nutritionists in the Department of Human Nutrition, Food and Animal Sciences,
College of Tropical Agriculture and Human Resources, UH-Manoa.
Dr. Dobbs also works with the University Health Service
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