Vitamin A Is a Balancing Act
Too much vitamin A might promote cancer, birth defects and bone loss. Too little makes you more prone to infections, vision problems and — yes, again –bone loss. What’s the right dose?
It’s confusing to describe, because food and supplements give you two forms of vitamin A: plant-derived beta-carotene that the body converts into vitamin A, and “preformed” animal-derived retinol.
Here’s the latest on both types:
- BETA-CAROTENE. You can’t depend on it for vitamin A activity. People convert from 0% to at best 11% of beta carotene into vitamin A, says biochemist Betty Burri of the USDA and the University of California at Davis. Megadoses may promote cancer, notably in heavy smokers.
- Bottom line: Smokers shouldn’t take pure beta-carotene supplements, Burri says. All others should avoid high doses (30 milligrams or more daily) except on the advice of a health professional. Instead, eat fruits and vegetables, especially carrots, spinach and sweet potatoes. Chop or mash them, and add a little fat to up the odds of absorption.
- RETINOL. Too much is toxic, harms the liver and may promote birth defects. Whether it weakens bones is a new controversy. In a Harvard study, getting more than 10,000 IU of vitamin A daily (as from liver, milk and supplements) hiked fracture risk 48% in older women, prompting advice to limit supplements to 5,000 IU daily. However, two recent studies did not find a link between high intake of vitamin A and lower bone mineral density or increased fractures in older women.
- Bottom line: Restrict intake to 10,000 IU daily, the upper “safe” limit set by the Institute of Medicine. Beware of liver: Eating just 1 ounce brings you to the limit.
This EatSmart column is reprinted from USAWEEKEND Magazine and is copyrighted by Jean Carper. It cannot be reprinted without permission from Jean Carper.
