Carotenoids are red, orange, and yellow pigments found in fruits and vegetables. About 600 carotenoids have been identified. All of them have antioxidant properties; some of them can be converted in the body to vitamin A , and these are called “provitamin A” carotenoids.
Many proponents of alternative medicine considered this outcome paradoxical, and attempted to explain it away in various ways:
- Beta-carotene alone may not be as useful as mixed carotenoids (and other healthful substances) found in fruits and vegetables.
- Synthetic beta-carotene may be less effective than natural beta-carotene.
- The participants in these studies were the wrong group of people (generally, smokers).
However, while any of these explanations may be correct, it is also quite possible that carotenoids simply do not provide any of the healthful effects attributed to them. Observational studies are notoriously unreliable for proving a treatment effective. Such studies only find associations between events, rather than cause and effect. It is quite possible, for example, that people who tend to eat more fruits and vegetables may be healthier in various other ways than those who do not, and that these other factors account for the apparent improvements. Consider the history of medical beliefs about hormone replacement therapy (HRT) for menopausal women. Observational studies had found evidence that women who used hormone replacement therapy had less heart disease, and on this basis millions of women were prescribed HRT. However, when proper double-blind studies were done, the results indicated that HRT actually caused heart disease. (For information on why double-blind studies are the best type of study, see Why Does This Database Rely on Double-blind Studies? )
- Reviewer: EBSCO CAM Review Board
- Review Date: 07/2012 -
- Update Date: 07/25/2012 -