Antioxidants and the prevention of hormonally regulated cancer

Epidemiological studies provide convincing evidence that a diet rich in antioxidant-containing foods, mostly fruits and vegetables, is associated with a lower incidence of most cancers, but results on hormonally regulated cancers, such as breast and prostate cancer, are inconsistent. Although studies in animals and cell cultures affirm the cancer preventive potential of single and/or combined antioxidant supplements, most intervention trials using supplementation with single or multiple antioxidant nutrients, given at relatively high doses, have not shown a consistent effect in reducing cancer risk. Intervention with a vitamin E supplementation reduced the risk of colorectal adenomas and prostate cancer and selenium supplementation reduced the incidence of total cancer, prostate, lung and colorectal cancer. Differences between the sexes in the reduction of cancer risk following antioxidant supplementation are partly due to differences in baseline values, metabolism and hormonal regulation. Among phytochemicals that have high antioxidant activity, garlic, aged garlic extract, flavonoids, carotenoids, and compounds found in brassica vegetables have shown anti-cancer effects. In human studies high serum levels of total carotenoids, beta-carotene and lycopene were linked to lower risk of breast cancer. Diets high in lycopene or brassica vegetables reduced the risk of prostate cancer. High intakes of allium vegetables (onion and garlic) reduced the risk of gastrointestinal and prostate cancer. A wide range of flavonoids from a variety of foods was shown to reduce the risk of gastrointestinal and respiratory tract cancer and a high intake of green tea to reduce the risk of breast cancer in Asian women.