Indole-3-carbinol is one of the major anticancer substances found in cruciferous (cabbage family) vegetables. It is a member of the class of sulfur-containing chemicals called glucosinolates.1 It is formed from parent compounds whenever cruciferous vegetables are crushed or cooked.2 3
Indole-3-carbinol and other glucosinolates (e.g., other indoles and isothiocyanates such as sulforaphane) are antioxidants and potent stimulators of natural detoxifying enzymes in the body.4 5 Indole-3-carbinol and other glucosinolates are believed to be responsible for the lowered risk of cancer in humans that is associated with the consumption of broccoli and other cruciferous vegetables like cauliflower, cabbage, and kale.6 7 8 9 10 11 12
Feeding indole-3-carbinol or broccoli extracts rich in indole-3-carbinol has dramatically reduced the frequency, size, and number of tumors in laboratory rats exposed to a carcinogen. It appears to be especially protective against breast13 14 15 16 and cervical17 18 cancers because of a number of actions, including an ability to increase the breakdown of estrogen. However, while most animal studies report protective effects, a few indicate that indole-3-carbinol may actually promote cancer formation in certain situations, depending upon the chemical initiator of cancer, method of exposure, and species of animal studied.19 20
Until there is further research and more human clinical data to determine if indole-3-carbinol actually inhibits rather than stimulates cancer formation, some researchers have recommended proceeding with caution when using isolated indole-3-carbinol as a dietary supplement.21 The areas where its use has currently been documented in humans are only preliminary, but the results are promising. Indole-3-carbinol reduced or halted the formation of precancerous lesions (papillomas) in 12 out of 18 people with recurrent respiratory tract papillomas.22 In addition, in a small double-blind trial, supplementation with 200 or 400 mg of indole-3-carbinol per day for 12 weeks reversed early-stage cervical cancer in 8 of 17 women.23 Preliminary studies have also shown indole-3-carbinol has significantly increased the conversion of estrogen from cancer-producing forms to nontoxic breakdown products.24 25
Where is it found?
Indole-3-carbinol is found in highest concentrations in broccoli, but is also found in other cruciferous vegetables, such as cauliflower, cabbage, and kale.