A Recommended Dietary Allowance for Carotene?

Do carotenoids--the bright red, yellow and orange pigments in fruits and vegetables--warrant a Recommended Dietary Allowance? New findings about the thyroid and oxidation could bring researchers closer to answering this question.

Two Agricultural Research Service experiments with female volunteers examined effects of meals low in carotenes. The experiments--one lasting 14 weeks and the other, 17 weeks--were the longest and most rigidly controlled low-carotene studies using human volunteers. A dozen women participated in each study.

Thyroxine, a key thyroid hormone, increased when the women ate few carotenes or other carotenoids at mealtimes. This finding adds to the few previously known links between carotenes and the thyroid.

Researchers also found more evidence suggesting carotenes act as antioxidants to protect the body from harmful oxidation. Antioxidants are thought to help prevent heart attack, stroke and cancer. During the low-carotene stints, researchers recorded several biochemical signs of oxidative damage. For example, they found more carbonyl compounds--breakdown products of oxidation--in the volunteers' blood and breath. The scientists apparently were the first to note these changes in humans in a carotenoid study that featured familiar foods. Later experiments elsewhere found similar results.

Further ARS studies will try to shed more light on whether a specific minimum daily intake of carotenoids is important for good health.

Scientific contact: Betty J. Burri , Western Human Nutrition Research Center, Agricultural Research Service, USDA, San Francisco, Calif., phone (415) 556-6285.