The ABC's of the RDA
A fat-soluble vitamin, A is important for healthy skin, good vision, and resistance to infection. It also appears to have antioxidant properties. It comes in two forms: retinol, which the body can readily use, and is found in butter fat, cod liver oil, liver, and egg yolks; and as "previtamins" called carotenoids, some of which the body converts into vitamin A. Carotenoids include beta carotene. They are found in orange, dark yellow, and dark green fruits and vegetables (such as carrots, sweet potatoes, apricots, and spinach).
Hopkins has a tremendous legacy in vitamin A research. Elmer V. McCollum, who would go on to become the chair of Biochemistry at Hopkins, announced the discovery of fat-soluble vitamin A in 1913 while working at the Wisconsin Agricultural Experiment Station. McCollum reported that lab rats deprived of vitamin A-containing foods developed eye lesions and infections, and failed to grow. At Hopkins, he spoke publicly about and wrote numerous popular articles on nutrition. Thanks partly to his congressional testimony, milk is now fortified with vitamins A and D.
In studies in Asia in the 1970s and '80s, Hopkins epidemiologist and ophthalmologist Al Sommer demonstrated that vitamin A can prevent xerophthalmia, a blinding disease that once affected hundreds of thousands of children, mainly in developing countries. Sommer, who is now dean of the School of Public Health then demonstrated that vitamin A supplementation also dramatically reduces the childhood death rate. International health agencies now widely employ vitamin A capsules as a disease prevention tool.
What's New at Hopkins:
In a recent study in Nepal, Hopkins public health researcher Keith West found that low-dose vitamin A or beta carotene capsules reduced mortality of pregnant women by an average of 44 percent. (Pregnancy-related problems claim 500,000 women each year worldwide, mainly in developing countries. In Nepal, the maternal mortality rate is at least 70 times the U.S. rate.) Researchers are still investigating the mechanism underlying the vitamin A miracle. One possibility: supplements reduce the risk of infection, a leading cause of maternal mortality.
What We Can Do:
Although researchers are studying the immune-boosting and antioxidant properties of vitamin A, experts advise caution in taking supplements, especially for pregnant women. Where this vitamin is concerned, there is a narrow barrier between a safe and toxic dose. Excess A can cause liver damage, hair loss, and brittle nails. Only a few times the recommended levels can cause birth defects. For now, the safest thing to do is consume foods that are rich in vitamin A, such as those listed above, as well as milk, bread, or cereals that are vitamin A-fortified. --MH
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