Supplement Forms/Alternate Names :

  • I3C


Principal Proposed Uses

Other Proposed Uses

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 1-3,6
  • Partially blocking the effects of estrogen on cells 4,6,30
  • Directly killing or inhibiting cancer cells 6
  • Reducing levels of free radicals, which can promote cancer by damaging DNA 5


I3C is found in cruciferous vegetables ( Brassica plants), 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. 7,8

Therapeutic Dosages

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. 9 Another study found benefits with 400 mg of I3C per day. 10 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 .)

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