Cancer Protective Supplements?

I had a saliva test that showed a high level of estrone. My general practitioner prescribed indole-3-carbinol (I3C) plus DIM (di-indolyl-methane). I’ve read that in lab studies those supplements have actually caused cancer in some animals. Do you feel that I3C and DIM are safe and effective supplements?

– July 30, 2009

First of all, I don’t believe that saliva tests are accurate or reliable, so if I were you, I wouldn’t make any treatment decisions based on those results.

Indole-3-carbinol (I3C) is a compound that occurs naturally in broccoli, cabbage, and other cruciferous vegetables including Brussels sprouts, turnips, kale, cauliflower, and watercress. Some research in animals suggests that I3C inhibits the development of cancers of the breast, stomach, colon, lung and liver.

I discussed your question with my colleague Victoria Maizes, M.D., executive director of the Arizona Center for Integrative Medicine. She told me that the National Institutes of Health is currently engaged in research to determine whether I3C can prevent breast cancer, and noted that there is a concern that it could actually promote rather than prevent cancer if a tumor already exists. As things now stand, she believes that I3C is "not ready for prime time" and does not recommend it to her patients. Dr. Maizes added that there is even less research on DIM than there is on I3C. Instead of taking either of these two supplements, she recommends that her patients eat cruciferous vegetables to protect themselves from cancer.

Population studies have shown that people who eat a lot of broccoli and other cruciferous vegetables have lower rates of cancer than those who don’t. Unfortunately, we don’t yet know what constituents of these vegetables are responsible for the protective effect. It may be I3C, the carotenoid pigments, vitamin C, or sulforaphane, a compound thought to suppress tumors. Or the cancer-protective effects may be due to two or more of these components acting together.

Until we have more information on the benefits of taking I3C as a dietary supplement, I agree with Dr. Maizes’ recommendation: eating plenty of cruciferous vegetables will give you many proven cancer-fighting compounds, all in safe, affordable forms.

Andrew Weil, M.D.

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