A Recommended Dietary Allowance for Carotene?
November 25, 1996
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
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)