DIM supplement: what it does and who should avoid it
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- DIM 200 mg capsules. Best for: Adults whose doctor has approved trying DIM. See options on Amazon
- Lower-dose DIM capsules. Best for: People who want a smaller amount. See options on Amazon
- Indole-3-carbinol (I3C) capsules. Best for: People comparing DIM with its parent compound. See options on Amazon
What DIM is
MSK's About Herbs database explains that DIM is a breakdown product of indole-3-carbinol (I3C), a compound in cruciferous vegetables. It is the most studied I3C metabolite. Food sources include broccoli, Brussels sprouts, cauliflower and cabbage.
After a week of oral DIM, its breakdown products appeared in human blood and urine within 10 to 12 hours. Supplements are sold mainly for estrogen metabolism, detoxification and cancer prevention claims.
What the research shows
| Use | What MSK reports |
|---|---|
| Estrogen metabolism | Small studies show changes in pre- and postmenopausal women |
| Prostate cancer | Limited data; possible benefit in castration-resistant disease |
| Cervical cell changes | Mixed results |
| Breast cancer with tamoxifen | Better estrogen metabolite ratio, but lower tamoxifen metabolites |
| Bone, inflammation | Preclinical only |
Estrogen. Small studies suggest DIM changes how estrogen is broken down in premenopausal women and in postmenopausal women with a history of early-stage breast cancer. Changing urine hormone metabolites is not the same as proving a health benefit.
Cancer. Lab studies show anti-inflammatory and anti-cancer effects. In people, limited data suggest daily DIM may help some men with castration-resistant prostate cancer by blocking the androgen receptor, while studies in women with abnormal cervical cells are mixed.
The tamoxifen concern
In a randomized trial of women with estrogen receptor-positive breast cancer taking tamoxifen, daily DIM shifted estrogen metabolism toward the 2-hydroxyestrone form linked with lower tumor risk. But it also lowered the level of endoxifen, an active form of tamoxifen that binds estrogen receptors more strongly. MSK says more research is needed on how DIM affects tamoxifen's effectiveness. Anyone on tamoxifen or other hormone therapy should not take DIM without talking with their oncologist.
DIM vs indole-3-carbinol (I3C)
I3C is the parent compound in cruciferous vegetables. NOW Foods explains that in the acidic stomach, I3C is readily converted into DIM plus other compounds. MSK notes DIM is thought to be superior to I3C for chemoprotection against breast and prostate cancers, though this comes mainly from lab and early research.
I3C supplements differ from DIM products. NOW Foods' I3C, for example, combines 200 mg I3C with 200 mg flax seed lignan extract, is taken 1 to 2 times daily with food, and may cause digestive upset in sensitive people. Either way, the same hormone cautions apply.
Effects in men. MSK reports DIM has shown androgen-blocking effects, which is why it is studied in prostate cancer. Men considering DIM for hormone reasons should talk with their doctor too.
Safety
- Pregnancy and nursing. MSK says women who are pregnant, planning pregnancy or nursing should not take DIM because of its hormonal effects. NOW Foods' label says the same.
- Birth control pills. Consult a health professional before use.
- Vision. A case of central serous chorioretinopathy, a fluid buildup under the retina, occurred after excessive daily DIM for 2 months and resolved 8 weeks after stopping.
- Blood clots and stroke. Case reports link DIM use to an ischemic stroke in a 38-year-old woman and a pulmonary embolism with deep vein thrombosis in a 65-year-old man.
- Skin. A severe rash with eosinophilia and body-wide symptoms has been reported.
- Lab tests. DIM alters estrogen metabolites in urine, so tell your doctor before hormone testing.
How to choose a DIM supplement
- Check the dose. NOW Foods' DIM 200 gives 200 mg DIM per capsule, taken once daily with a meal.
- Check extras. That product also contains 100 mg calcium D-glucarate and 20 mg sodium copper chlorophyllin. Other brands add ingredients such as BioPerine or pomegranate.
- Food first. Cruciferous vegetables supply the parent compound naturally.
- Avoid if pregnant, trying to conceive, nursing or on tamoxifen unless your doctor approves.
- Talk with your doctor about hormone symptoms rather than self-treating.
What to look for when you buy
DIM 200 mg capsules
Best for: Adults whose doctor has approved trying DIM
NOW Foods lists 200 mg DIM per capsule with calcium D-glucarate and chlorophyllin, taken once daily with a meal.
Watch out: Not for pregnancy, trying to conceive or nursing. Ask your doctor if on birth control or tamoxifen.
See options on AmazonLower-dose DIM capsules
Best for: People who want a smaller amount
DIM is also sold in lower strengths such as 100 mg.
Watch out: Same hormonal cautions. Rare serious reactions have been reported.
See options on AmazonIndole-3-carbinol (I3C) capsules
Best for: People comparing DIM with its parent compound
DIM is made from I3C, found in cruciferous vegetables; NOW Foods sells I3C separately.
Watch out: Ask your doctor first; it shares DIM's hormonal concerns.
See options on AmazonQuestions people ask
- What does a DIM supplement do?
- It can change how estrogen is broken down. Whether that improves health has not been proven.
- Is DIM good for women?
- It is marketed for estrogen balance, but evidence is limited. Avoid it in pregnancy, when trying to conceive or while nursing.
- Can I take DIM with tamoxifen?
- Only with your oncologist's approval. DIM lowered endoxifen, an active tamoxifen form, in a clinical study.
- What are DIM side effects?
- Rare case reports include vision problems, severe rash, stroke and blood clots.
- Can I get DIM from food?
- Broccoli, Brussels sprouts, cauliflower and cabbage contain its parent compound, indole-3-carbinol.
Sources
- Diindolylmethane (mskcc.org), Memorial Sloan Kettering Cancer Center, About Herbs
- DIM 200 Diindolylmethane Veg Capsules (www.nowfoods.com/products/supplements/dim-200-diindolylmethane-veg-capsules), NOW Foods
- Indole-3-Carbinol (I3C) 200 mg Veg Capsules (www.nowfoods.com/products/supplements/indole-3-carbinol-i3c-200-mg-veg-capsules), NOW Foods