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 ef