DIM (diindolylmethane)

DIM (diindolylmethane)

DIM is a phytochemical that is found in broccoli, cabbage, turnip and mustard greens, kale, brussel sprouts, collards, etc. "The first development in this research using chemically altered [sic] DIM from broccoli came when the growth of breast cancer cells was inhibited in laboratory studies. Subsequent research showed these compounds also inhibited growth of pancreatic, colon, bladder and ovarian cancer cells in culture, Safe said. Limited trials on lab mice and rats have produced the similar results, he noted." "Researchers from the University of California at Berkeley looked at the effects of broccoli on human breast cancer cells. According to findings, compounds in broccoli known as indoles are digested and broken down in the stomach to a compound called 3,3'-diindolylmethane (DIM). This compound may be the key to keeping cancer at bay."

The Cruciferous Choice: DIM or 13C? Phytonutrient Supplements for Cancer Prevention and Health Promotion

Cruciferous vegetable phyto-nutrients include natural substances whose supplemental use has great potential for the prevention of human cancer. The additional discovery that the cruciferous indoles, diindolyl-methane (DIM®) and indole-3-carbinol (I3C), also promote healthy estrogen metabolism has expanded their usefulness as dietary supplements for many estrogen-related conditions. Beyond cancer prevention, effective uses of absorbable DIM have included benefits for perimenopausal women, in premenstrual syndrome (PMS), in endometriosis, and in cervical dysplasia. Also benefited from supplementation are women on estrogen replacement (HRT), as well as men with estrogen-related conditions including prostate hypertrophy. In choosing dietary supplement formulations containing DIM or I3C, it is important to understand basic differences in their phytochemical characteristics and interaction potential. These differences have important implications as to their relative safety for long-term use.

Introduction to the Cruciferous, Indole Phytonutrients

Cruciferous vegetables (broccoli, cabbage, cauliflower, Brussels sprouts, bok choy) are in the news as powerful sources of cancer-preventive phytonutrition. A recent study of Seattle men showed that three or more servings of cruciferous vegetables a week can reduce prostate cancer risk almost by half.[ 1] For women however, the news is not so clear. In a large prospective study of 350,000 women, no protection from breast cancer could be attributed to dietary fruits and vegetables, or to the highest intake of cruciferous vegetables.[ 2] Since other controlled studies in women have documented clear, beneficial action from cruciferous dietary supplements,[ 3] there is a growing basis for adding cruciferous phytonutrients to the fruits and vegetables of a healthy diet. The active substances in cruciferous vegetables benefiting estrogen-related disorders have proven to be absorbable diindolylmethane (DIM®) and its precursor indole-3-carbinol (I3C).[ 4] Supplemental use of these substances has a long history in cancer prevention research. With expanding applications in preventive nutrition, their use in women has actually been shown to reduce risk status for breast cancer,[ 5] and cause the regression and disappearance of advanced cervical dysplasia.[ 6] The supplemental use of DIM and I3C are under active investigation.[ 7] These natural products are increasingly available as dietary supplements for healthier estrogen metabolism, peri-menopause, men's health and cancer risk-reduction.
Significant amounts of DIM are found in cruciferous plants following crushing.[ 8] This is unlike I3C which, due to its unstable nature, is only transiently present, primarily during digestion.[ 9] I3C is the natural precursor to DIM, which is formed from a "condensation reaction" in which one I3C molecule combines with another. The resulting DIM is a "di-indole" or double molecule formed from two I3C molecules. Release of active DIM is facilitated by enzymes in the plant and is also due to the action of gastric acid on I3C released during digestion. Pure forms of these natural substances derived from plant-based precursors are now available as dietary supplements. The choice of precursor I3C, or active DIM as a supplement requires an understanding of their relative merits and safety as phytonutrients. This review will compare and contrast the important differences between DIM and I3C.

DIM and I3C - Different Physical and Phytochemical Characteristics

Based on well known physical characteristics, DIM is very stable in water and acid but highly insoluble. I3C is soluble but highly reactive, resulting in over 20 condensation products, including DIM, after I3C is exposed to stomach acid.[ 10] When I3C is kept dissolved in water, or buffered in weakly acidic solutions, a greater conversion to DIM occurs. DIM requires a special dietary supplement formulation to provide for improved solubility and complete gastrointestinal absorption. I3C requires careful storage, avoiding heat, moisture and light to slow its rapid breakdown on the shelf. Taken as a dietary supplement, I3C requires gastric acid for conversion to active products. I3C is more irritating to the stomach than DIM, due to its chemical reactivity.[ 11] I3C is much more sensitive to interaction with components of food, especially vitamin C, which limit its conversion into DIM and other condensation products. Conversion from I3C into DIM not only requires a precise acidity, it requ ires time. This conversion may proceed slowly, requiring more than a typical intestinal transit time to be complete.

A compelling study favoring the use of DIM over I3C demonstrated the fact that following an oral dose of I3C in humans only DIM and no I3C was found circulating in the bloodstream of test subjects.[ 12] This finding confirms that I3C disappears after entry into our stomachs, and since a highly sensitive detection method was used, no direct benefits can be attributed to absorbed I3C. Based on this study it is also documented that over 90% of an oral dose of I3C goes unaccounted for in the form of non-DIM "condensation products" of uncertain structure, uptake and activity.
A compelling study favoring the use of DIM over 13C demonstrated the fact that following an oral dose of 13C in humans only DIM and no 13C was found circulating in the bloodstream of test subjects.

Benefits for Healthy Estrogen Metabolism

The history of supplemental use of cruciferous vegetable phytonutrients begins over 20 years ago with research showing that either broccoli,[ 13] pure DIM,[ 14] or pure I3C[ 14] prevented chemically induced breast cancer in animals. In the last 10 years it has been discovered that supplemental use of both DIM and I3C is associated with a beneficial shift in estrogen metabolism.[ 15] Both specially formulated DIM[ 16] and I3C,[ 5] used as dietary supplements, have been shown to reliably increase the 2-hydroxylation of estrogen, increasing the 2/16 ratio of estrogen metabolites. This ratio (also known as the "good to bad" balance of estrogen[ 17]) has now been shown to be a predictor of future breast cancer in a prospective study of 5,000 Italian women.[ 18] In this study, the future risk of developing breast cancer over a 4 year period was reduced in the premenopausal women who demonstrated the highest 2/16 ratio. In a second study, a favorable ratio of higher 2/16 was also seen in benign cond itions compared to breast cancer cases which had lower ratios.[ 52]

A patented formulation of absorbable DIM,[ 19] has been shown to result in a significant increase in the 2/16 ratio at one tenth of the dose using I3C. Supplemental I3C at 300 or 400 mg/day is required by women to significantly increase the ratio.[ 5] Animal studies have clearly shown that it is DIM and not I3C that is the active promoter of greater 2-hydroxylation of estrogen which is associated with a cancer-resistant estrogen metabolism.[ 20]

Besides being the active phytonutrient promoting beneficial estrogen metabolism, DIM has now been shown to actually treat breast cancer in animals.[ 21] In this study, breast cancer was induced in animals with dimethylbenz-anthracene (DMBA). Once tumors were present DIM supplementation was begun. DIM, at the same dose now in use in human studies, completely stopped tumor growth. When the same study was conducted with I3C, using a dose 50 times greater than current human use, no effect on tumor growth was observed.[ 22] However I3C, like DIM,[ 14] has been shown to prevent the occurrence of breast cancer in animals. In separate studies, I3C was shown to prevent spontaneous[ 56] and induced[ 14, 57] breast cancer.

Apart from therapeutic potential, dietary supplement use of DIM and I3C relates to hormonal balance and symptoms of "estrogen dominance." Supplemental use requires consideration of long term safety. The reactivity, instability, and observed side effects from I3C raise questions and concerns about its safety in comparison to DIM.
How Does the Safety of Absorbable DIM Compare to Supplemental I3C?

DIM is less reactive and less of an enzyme inducer than I3C. This difference accounts for a number of the side effects seen with I3C. Doubling the typical dose of I3C from 400 to 800 mg/day causes dizziness and unsteady gait, signs of nervous system toxicity in humans.[ 23] Similar effects were observed during I3C use in animals.[ 24] No side effects of any sort are seen when pure DIM is used even in huge doses in animals, or when the usual dose of 40 mg/day of DIM (contained in 150 mg of absorbable, patented DIM) is tripled to 450 mg/day in human subjects.[ 25]

Safety concerns relate to the long-term use of I3C as a dietary supplement. These concerns with I3C have to do with its action as a non-specific inducer of powerful cytochrome enzymes responsible for "Phase I" detoxification metabolism.[ 26] Overactive Phase I metabolism may be a risk for activating potential carcinogens especially in the colony A study in rats has shown increased colon tumors in chemically treated rats given I3C as a dietary supplement.[ 28] One notable example of an unwanted product from I3C arising in stomach acid is indolocarbazole or ICZ.[ 29] ICZ is produced from I3C during digestion and resembles dioxin in structure and enzyme inducing activity. ICZ has been linked to oxidative DNA damage[ 30] and unwanted estrogen metabolites.[ 31] With more stable DIM, there is zero production of ICZ or other unwanted I3C reaction products. DIM is able to promote beneficial estrogen metabolism, and improve perimenopausal symptoms at a lower dose than I3C without creation of extraneous, reaction products of uncertain safety.

Since supplemental diindolyl-methane does not result in the wide array of enzyme induction that I3C provokes, there is less chance of interaction with other nutrients, hormones, or medications using diindolylmethane. With I3C, all antacids and heartburn medications will tend to change an individual's response to due to I3C's dependence on stomach pH for activation. Regarding its safe use in young women, diindolylmethane has been initially tested during combined use with oral contraceptives. Based on its lack of enzyme induction or inhibition, no problem interactions were seen.[ 32] I3C has not been tested with oral contraceptives, but its powerful enzyme inductive activities have great potential to alter the metabolism of both oral contraceptives, certain herbs, various prescription drugs, and hormones other than estrogen. In each side by side tests of I3C and diindolylmethane, I3C has proven to be the most enzyme inductive.[ 34, 53, 54] DIM is clearly a more specific modulator of enzyme activity than I3C.

Maintaining Healthy Testosterone in Perimenopause, PMS, and Male Aging

Differences in enzyme inducing activity of DIM versus I3C, impact the metabolic pathways for maintaining healthy testosterone balance in both women and men. I3C in animals has been shown to promote more rapid metabolism and inactivation of testosterone.[ 33] A recent comparison of I3C and absorbable DIM in an independently conducted safety test in animals,[ 34] showed that at the typical human dose, only I3C not DIM, promoted increased liver enzyme activity responsible for testosterone metabolism.[ 35] At higher doses for both I3C and DIM, dramatic increases in these and other enzyme activities were seen with I3C but not with DIM. The enzyme subtypes induced by I3C and typical substances influenced included: CYP2B1 (testosterone metabolism), CYP3A4 (oral contraceptives, testosterone, natural substances, drugs), CYP2C9 (anti-seizure medications), CYP2D6 (prescription drugs) and CYP2E1 (prescription drugs). As an inducer of CYP3A4 enzymes, I3C is acting in an analogous fashion to hypericin from extracts of St. John's wort (Hypericum perforatum).[ 36] St. John's wort preparations have been shown to accelerate the metabolism and clearance of anti-viral drugs used in HIV infection, the transplant immune-suppressant, cyclosporine, and the heart phytomedicine, digoxin.[ 37] I3C may possess similar activity but has not been tested clinically.
Perimenopause is a time in women's lives characterized by higher than normal estrogen production and lower progesterone production, especially during the second half or "luteal" phase of the menstrual cycle.[ 38] In women suffering from PMS (premenstrual syndrome), severity of symptoms is associated with the degree of estrogen elevation in affected women.[ 39] Also notable in perimenopausal women is a deficiency of "free" or unbound testosterone during the middle of the menstrual cycle.[ 40] Deficiency of testosterone is known to be associated with depressed mood, loss of libido, and weight gain. Resolution of symptoms with testosterone replacement in perimenopausal women confirms the importance of the delicate testosterone balance in middle aged women. Since free testosterone levels in women are 25 times lower than in men, even small changes in testosterone levels and protein binding can be associated with symptoms. As a supplement which helps support testosterone and progesterone level s, DIM is the preferred cruciferous indole for perimenopausal nutritional support. As a more efficient promoter of beneficial 2-hydroxy estrogen metabolism than I3C, DIM can more predictably and safely increase 2-hydroxy estrogen metabolites. These unique estrogen metabolites stimulate progesterone production,[ 55] and compete with testosterone for protein binding. This helps to maintain testosterone in its active, free form, specifically shown to support healthy mood and libido in women with PMS.[ 41]

Cruciferous Supplements for Men

The same dynamics for maintaining higher total and free testosterone levels apply to healthy aging in men. Estrogen metabolism is slowed during aging in men, especially in association with obesity and regular alcohol use. Avoiding overactive testosterone metabolism, and reducing the conversion of testosterone into estrogen are goals of nutritional support in middle aged and older men. It is well documented that estrogen accumulates in the prostate gland starting at age 50[ 42] and that estrogen is associated with the degree of prostate enlargement.[ 43] Based on animal and human testing, DIM is again preferable to I3C in the area of men's health. Using DIM in men avoids accelerating testosterone metabolism, especially regarding unwanted conversion of testosterone into estrogen. In the safety study reported,[ 34] I3C and not DIM increased activity of "aromatase" (CYP19), the enzyme responsible for converting testosterone into estrogen. Regarding men's health, supplementation with absorbab le DIM has resulted in reports of improved prostate function based on reduced nighttime urination in symptomatic older men.

Use of DIM vs I3C More Closely Resembles the Human Diet

Once absorbed, DIM is uniquely active in promoting healthy estrogen metabolism and improving symptoms of estrogen-related imbalance in both men and women. However, absorption of crystalline DIM by itself does not occur due to DIM's extreme lack of solubility from the crystalline state. In early testing, human volunteers took 300 mg of crystalline DIM for one week without a change in before and after measurements of urinary estrogen 2/16 metabolites. Subsequently, taking one tenth of this amount of DIM in an absorbable formulation (30 mg of DIM provided in 100 mg of formulation), caused significantly increased levels of beneficial 2-hydroxy estrogen metabolites in urine. 30 mg of DIM is about twice the amount of DIM obtainable from large daily portions of cruciferous vegetables. The absorption advantage for absorbable DIM,[ 16] allows an intake of DIM that is only 3-4 times more than the amount of DIM available from cruciferous vegetables alone. The use of this patented formulation effe ctively provides an absorbable amount of DIM equal to or above that found in two pounds of raw cabbage.

When I3C is used as a supplement, a maximum of 10% is converted to DIM, even if the I3C can be targeted to the higher pH environment of the upper intestine (duodenum). It is not surprising that a minimum of 300-400 mg/day of I3C is needed to dependably improve the 2/16 estrogen ratio,[ 5] since this would relate to 30-40 mg/day of DIM. The requirement for 300-400 mg/day of I3C puts the supplement dose at 30-40 times the possible dietary exposure to I3C equivalents. Many of the non-DIM condensation products from I3C are highly enzyme inducing.

Compatibility with Other Hormone Balancing Substances: Soy, Red Clover, Black Cohosh, and Chasteberry Extract
Soy, Red Clover, Black Cohosh, and Chasteberry are sources of phytonutrients utilized for their hormone modulating qualities. As seen with the interaction described for I3C and St. John's wort, the actions of CYP3A and CYP2B cytochrome enzymes are often involved in the metabolism of active phytochemicals.[ 36] The greater enzyme inductive effects of I3C compared to DIM creates a risk for overactive metabolism and elimination of desirable phytoestrogens. Ideally these substances should be able to be taken in conjunction with cruciferous phytonutrients. While both DIM and a triple molecule derived from I3C called the "Cyclic Trimer" have been noted to have estrogenic qualities,[ 44, 45] these actions have not been observed during human use. In fact neither DIM, I3C, nor the phytoestrogens listed above can substitute for the desirable activities of natural estrogen and estrogen's beneficial metabolites.

Regarding the potential of soy phytoestrogen for breast cancer prevention, a recent large study from Japan revealed no benefit, even after years of soy intake with more isoflavones than with regular use of isoflavone concentrates.[ 46] Though supplementation with approximately 200 mg/day of soy isoflavones has been shown to modestly increase the production of beneficial estrogen metabolites,[ 47] this is much less of an effect than that seen with absorbable DIM or I3C. Of more concern is the stimulation of breast cancer cell growth seen with phytoestrogens.[ 48] Most important are observations made in humans on soy supplementation. Normal women maintained on a soy supplemented diet showed significant hyper-proliferation of breast epithelial cells.[ 49] Unlike DIM and I3C, soy isoflavones do not inhibit chemically induced breast cancer in animals.[ 50] While phytoestrogens like the isoflavones found in soy and those found in red clover and black cohosh can be used in conjunction with DIM, t hey do not offer the same advantage in terms of beneficial modulation of estrogen action seen with DIM. As competitors to estrogen, phytoestrogens may interfere with normal estrogenic support for successful brain aging. Recent reports suggest that soy phytoestrogen intake may be associated with accelerated brain aging and cognitive decline in both women and men.[ 51] Unlike use of soy isoflavones, which can make breast symptoms worse, supplementation with absorbable DIM has been associated with improvement in premenstrual breast pain, and resolution of breast cysts. In addition, improved symptoms of PMS, improved cervical health as documented by normalized Pap Smears, and reduced menstrual pain are documented in association with absorbable DIM supplements. In both women and men, facilitated weight loss has been noted on lower carbohydrate diets at higher doses of absorbable DIM. None of these benefits have been observed with soy supplementation alone.

Summary and Conclusion

There are important differences in the phytonutrient characteristics of DIM and I3C. As a dietary supplement, absorbable DIM provides an active, known entity from cruciferous vegetables, augmenting DIM in the diet, and added to the diet at only 3 times more than dietary DIM levels. Use of I3C requires a 30 times greater dose of a more reactive and unpredictable phytochemical. The diverse products resulting from digestion of I3C may contribute to benefits but may also create safety risks. The table summarizes the risk and benefit profiles of absorbable DIM and I3C. Practitioners and patients should take note of the differences as they more widely turn to cruciferous phytonutrients for hormonal balance, healthy aging, and cancer prevention.


Michael A. Zeligs, MD BioResponse, LLC P.O. Box 288 Boulder, Colorado 80306 USA E-mail: zeligsmd@bio-response.com


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By Michael A. Zeligs

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