Epidemiological studies suggest that
cancer risk is related to dietary intake of
carotenoid-rich fruit and vegetables. Whether or not
carotenoids are the active component has yet to be definitively proven, although some of these studies have shown that after elimination of obvious factors, such as fibre content, these foods still possess anticancer properties. On the other hand, two large intervention studies have shown that
beta-carotene supplementation increases the risk of
lung cancer in smokers. However, high doses of
beta-carotene were used in these studies. Experimental work on animals and cells has shown that treatment with
carotenoids can inhibit the development of
cancer. Such studies have revealed a variety of mechanisms, in addition to
antioxidant and conversion to
vitamin A, including up-regulation of gap junctional communication, induction of detoxifying
enzymes and inhibition of proliferation. Studies on tumour cells indicate that
carotenoids can interfere with the growth of transformed cells, suggesting that they may be effective in the treatment of some
cancers.