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What is indole? Why do we need it?

Indole (also known as indole-3-carbinol) is a chemical found in leafy green vegetables that belong to the cabbage family. It is a member of a group of chemicals called glucosinates, and is created whenever cruciferous vegetables are crushed or cooked.

Indole is a powerful antioxidant. It is believed to be responsible for reducing the risk of cancer associated with people who consume large amounts of broccoli, cabbage, cauliflower and kale. In animal studies, indole appears to be especially effective against breast and cervical cancers because of its ability to increase the body's breakdown of estrogen. However, until future studies are conducted on humans, some researchers have recommended that indole be taken as a dietary supplement only with extreme caution.

How much indole should I take?

The amount of indole to be consumed depends on the condition being treated. Most animal studies examining the role of indole in breast cancer have used dosages ranging from 300 mg to 400 mg per day. Because indole is not an essential nutrient, recommended daily allowances have yet to be established.

What forms of indole are available?

Indole is available in a variety of cruciferous vegetables, such as kale, cauliflower and cabbage. It is available in its highest concentration in broccoli. In addition, indole is available as a dietary supplement, and can be found at many health food stores.

What can happen if I take too much indole? Are there any interactions I should be aware of? What precautions should I take?

As of this writing, there are no known side-effects associated with taking indole, nor are there any known drug interactions associated with indole. Because relatively few studies conducted on humans, some researchers have recommended that indole be taken as a dietary supplement only under the supervision of a health care provider. As always, make sure to consult with a licensed health care provider before taking indole or any other herbal remedy or dietary supplement.


  • Bradlow HL, Sepkovic DW, Telang NT, et al. Multifunctional aspects of the action of indole-3-carbinol as an antitumor agent. Ann N Y Acad Sci 1999;889:204-13.
  • Broadbent TA, Broadbent HS. The chemistry and pharmacology of indole-3-carbinol (indole-3-methanol) and 3-(methoxymethyl) indole. Part I. Curr Med Chem 1998;5:337-52.
  • Plumb GW, Lambert N, Chambers SJ, et al. Are whole extracts and purified glucosinolates from cruciferous vegetables antioxidants? Free Radic Res 1996;25:75-86.
  • Verhoeven DT, Goldbohm RA, van Poppel G, et al. A review of mechanisms underlying anticarcinogenicity by brassica vegetables. Chem Biol Interact 1997;103:79-129.
  • Yuan F, Chen DZ, Liu K, et al. Anti-estrogenic activities of indole-3-carbinol in cervical cells: implication for prevention of cervical cancer. Anticancer Res 1999;19(3A):1673-80.
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