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.