Between cod-liver oil capsules and a multivitamin, I get 5,500 international units (IU) per day of vitamin A in the retinol form. Could that be harmful? —M.K., El Segundo, Calif.

Yes. The body gets vitamin A in two forms: from retinol, or "preformed" vitamin A, and from beta-carotene, which the body converts into vitamin A. Over time, a high intake of retinol can cause nervous-system and liver damage and increase the risk of birth defects, hip fractures, and premature death. That’s why men and women should get no more than 3,000 IU or 2,300 IU of retinol a day, respectively. Since the evidence on cod-liver oil is limited—just a few studies suggesting that it may reduce depression and certain risk factors for heart disease—you should probably skip it given its retinol content (about 1,250 IU in a typical gel-cap supplement). And ask your doctor about having your blood tested for excessive levels of the vitamin.