Indole-3-Carbinol Overview

Indole-3-carbinol (I3C), a chemical found in vegetables of the broccoli family, is thought to possess cancer preventive properties.

Indole-3-carbinol appears to work in several ways:

• Facilitating the conversion of estrogen to a less cancer-promoting form ¹
• Partially blocking the effects of estrogen on cells ²
• Directly killing or inhibiting cancer cells ³
• Reducing levels of free radicals, which can promote cancer by damaging DNA ⁴

I3C is found in cruciferous vegetables ( Brassicaplants), such as cabbage, broccoli, brussels sprouts, cauliflower, kale, kohlrabi, and turnips. A typical Japanese diet provides the equivalent of about 112 mg of I3C daily; intake in Western diets is lower. ⁵

A 4-week, double-blind, placebo-controlled trial of 57 women found that a minimum dose of 300 mg of I3C daily may be necessary to reduce risk of estrogen-promoted cancers. ⁶ Another study found benefits with 400 mg of I3C per day. ⁷ However, until the overall effects of I3C are better understood, we recommend obtaining this substance through consumption of broccoli family vegetables rather than taking it as a supplement. (See Safety Issues .)

A 12-week, placebo-controlled trial of 30 women with stage II or III cervical dysplasia found that treatment with I3C at a daily dose of 200 or 400 mg significantly improved the rate at which the cervix spontaneously returned to normal. ⁸

1. Michnovicz JJ. Increased estrogen 2-hydroxylation in obese women using oral indole-3-carbinol. Int J Obes Relat Metab Disord. 22(3):227-9.
2. Yuan F, Chen DZ, Liu K, Sepkovic DW, Bradlow HL, Auborn K. Anti-estrogenic activities of indole-3-carbinol in cervical cells: implication for prevention of cervical cancer. Anticancer Res. 19(3A):1673-80.
3. Bradlow HL, Sepkovic DW, Telang NT, Osborne MP. Multifunctional aspects of the action of indole-3-carbinol as an antitumor agent. Ann N Y Acad Sci. 889():204-13.
4. Arnao MB, Sanchez-Bravo J, Acosta M. Indole-3-carbinol as a scavenger of free radicals. Biochem Mol Biol Int. 39(6):1125-34.
5. Heaney RK, Fenwick GR. Natural toxins and protective factors in brassica species, including rapeseed. Nat Toxins. 3(4):233-7; discussion 242.
6. Wong GY, Bradlow L, Sepkovic D, Mehl S, Mailman J, Osborne MP. Dose-ranging study of indole-3-carbinol for breast cancer prevention. J Cell Biochem Suppl. 28-29():111-6.
7. Bell MC, Crowley-Nowick P, Bradlow HL, Sepkovic DW, Schmidt-Grimminger D, Howell P, Mayeaux EJ, Tucker A, Turbat-Herrera EA, Mathis JM. Placebo-controlled trial of indole-3-carbinol in the treatment of CIN. Gynecol Oncol. 78(2):123-9.
8. Bell MC, Crowley-Nowick P, Bradlow HL, Sepkovic DW, Schmidt-Grimminger D, Howell P, Mayeaux EJ, Tucker A, Turbat-Herrera EA, Mathis JM. Placebo-controlled trial of indole-3-carbinol in the treatment of CIN. Gynecol Oncol. 78(2):123-9.