November 2001 Issue of Nutrition Science News
New research pinpoints how nutrition may prevent estrogen's carcinogenic activity by directing metabolites down favorable pathways
By Dan Lukaczer, N.D.
The continuing controversy over the health benefits and risks of estrogen is a complex and evolving story. Part of the reason is because estrogen is a much more complicated substance than originally believed. Although most people think of estrogen as a single entity, these hormones are actually three biochemically distinct molecules the body produces naturally—estrone (E1), estradiol (E2), and estriol (E3). These three estrogen molecules have different activities that make them more or less "estrogenic." The estrogenic activity often determines the mutagenic or carcinogenic potential of an estrogen.
It is widely believed that cumulative estrogen exposure is the most critical breast cancer risk factor. Breast cancer risk increases with early menarche, late menopause, long-term use of birth control pills, and estrogen replacement therapy.1 When women gain weight, grow taller, have fewer children (and have them later in life), they increase their lifetime exposure to estrogen, and its associated risks.
Researchers are gaining new insights into the processes through which E1, E2, and E3 are metabolized, detoxified, and excreted. These estrogens break down or are detoxified into estrogen metabolites—daughter compounds—called 2-hydroxyestrone, 4-hydroxyestrone, and 16-hydroxyestrone. These metabolites can have stronger or weaker estrogenic activity—and thus increase a woman's risk of breast, uterine, and other cancers—depending on how they are metabolized.
We know estrogen metabolism depends on three factors:
a woman's genetic makeup, lifestyle and diet, and environment. Therefore, understanding estrogen metabolism, and the things we can do to affect it, offers significant opportunities to reduce cancer risks, particularly of breast and uterine cancers.
Estrogen Metabolism
In premenopausal women, the ovaries produce the estrogen estradiol (E2), which converts into estrone (E1), both of which must eventually be broken down and excreted from the body. This breakdown occurs primarily in the liver, and the excreted metabolites flow out in the bile or urine. Estradiol and estrone undergo this breakdown through a process called hydroxylation, an enzymatic activity in which the parent estrogen is transformed by the addition of a hydroxyl (OH) group at specific positions on estrogen's molecular ring.
Estrogen molecules are composed of carbon ring structures that are named numerically. Estradiol has 17 carbon atoms and can be hydroxylated at particular points on that ring. Considerable research has shown that major metabolites of estradiol and estrone are those hydroxylated at either the C-2 or the C-16 positions. Hydroxylated metabolites at the C-4 position also are present, but in lesser amounts. We might think of this process as parent estrogens (estradiol and estrone) begetting daughter estrogens (C-2, C-4, and C-16 hydroxyestrones and hydroxyestradiols). The problem is, some of these are the proverbial good daughters and some are bad daughters. I'll describe how the "bad" daughters can cause significant trouble.
What makes an estrogen good or bad? That has to do with the biological activity, or potency, of that estrogen. Estrogens are important in a host of cellular activities that affect growth and differentiation in various target cells. This is normal and beneficial, but too much estrogenic stimulation can have a negative effect. Therefore, properly metabolizing and excreting estrogens is crucial. This is how the daughter compounds differ substantially. If these estrogens are metabolized into the 2-hydroxylated estrone and estradiol, they lose much of their cell proliferative and estrogenic activity and are termed "good" estrogen metabolites. Studies show that when 2-hydroxylation increases, the body resists cancer, and that when 2-hydroxylation decreases, cancer risk increases.
However, the C-4 and C-16 hydroxylated estrone and estradiol metabolites are different from C-2 because these metabolites have more estrogenic activity than their mother compound.3 Research strongly suggests that women who metabolize a larger proportion of their estrogens down the C-16 pathway, as opposed to the C-2 pathway, have elevated breast cancer risk,4 and that the daughter estrogens metabolized down the C-16 route may be associated with direct genotoxic effects and carcinogenicity.5
Predicting Cancer Risks
In one recent large trial of 10,786 premenopausal women at the State University of New York at Buffalo, researchers found that those who went on to develop breast cancer had significantly less 2-hydroxyestrone and more 16-alphahydroxyestrone metabolites than women who did not. Following women for 5.5 years, they found that participants with increased levels of 2-hydroxyestrone had a 40 percent decrease in the occurrence of breast cancer.6
In a longer-term study on postmenopausal women, women with the highest C-2:C-16 ratio (a higher ratio means more C-2 and less C-16, proportionally) had 30 percent less risk of developing breast cancer than women with lower ratios.7 With this information, it would seem useful to discover what, if any, dietary or lifestyle modifications could guide estrogens down the C-2 pathway.
Estrogens are metabolized by a series of oxidizing enzymes in the cytochrome P450 family. These are the detoxification enzymes that break down all manner of drugs, hormones, and environmental toxins into generally less harmful metabolites. By closely studying this family of 30 or so enzymes, scientists have discovered how the parent estrogen compounds are modified in the C-2, C-4, or C-16 pathways. Researchers found that if particular enzymes within this family, namely cytochrome P450 1A1 and 1A2, are activated or stimulated, then more parent estrogens are metabolized into C-2-hydroxylated compounds.8 However, if cytochrome P450 3A4 and 1B1 are activated, then more C-4 and C-16 are produced9. The C-16-alpha version tends to damage DNA and cause abnormal cellular proliferation, while the C-2 metabolite has less estrogenic activity.2-4 If the proportion of C-16-alpha-hydroxyestrone can be decreased while the C-2-hydroxyestrone is increased—changing the ratio between the two—cancer risk could be reduced.
Nutrition And Estrogen
Epidemiological studies suggest the protective effects of soy protein on breast cancer rates in Asian countries where soy is a dietary mainstay.10 While soy protein is a complex mixture of nutrients and phytochemicals, it appears that part of its benefit is related to the isoflavones genistein and daidzein. Studies suggest that they change the way estrogens are metabolized, therefore changing the C-2:C-16 ratio. In studies on both pre- and postmenopausal women, it has been shown that isoflavones increase the beneficial C-2-hydroxyestrone at the expense of the C-16-hydroxyestrone, therefore increasing the C-2:C-16 ratio.11,12
It appears that isoflavones found in other plants might also have beneficial effects. Kudzu (Pueraria lobata), a vine found in the southern United States, contains unique isoflavones. It was found that one of kudzu's isoflavones—puerarin—induced cytochrome P450 enzymes 1A1 and 1A2, among others, which pushed estrogen through the beneficial C-2-hydroxylation metabolic pathway.13
Lignans found in fiber-rich foods such as seeds and grains, and in particularly high concentrations in flaxseeds, contain phytochemicals that, when acted upon by bacteria in the gut, are converted to the metabolites called enterolactone and enterodiol, which appear to have similar effects as isoflavones. Researchers have demonstrated in animal and cell studies that lignans have chemoprotective effects, and they may influence estrogen production and metabolism.14,15 Studies also have shown that women with breast cancer, or at risk for breast cancer, have low excretion levels of urinary lignans. In cell-culture studies, lignans have been shown to inhibit estrogen-sensitive breast cancer cell proliferation.14 When flax was supplemented at five and 10 grams per day for three seven-week periods in a group of 28 postmenopausal women, the levels of C-2 hydroxyestrone increased in the urine, which increased the ratio of C-2:C-16.15 This suggests that flax may have a beneficial effect on estrogen metabolism.
The Phytonutrient I3C
The results of epidemiological studies on cruciferous and mustard family vegetables (Brassica genus)—including bok choy, broccoli, brussels sprouts, cabbage, cauliflower, kale, kohlrabi, mustard, rutabaga, and turnip—suggest that diets high in these vegetables lower the breast cancer rate. Increasing the amount of cruciferous vegetables in the diet can increase the C-2: C-16-estrogen ratio.16 The vegetables' phytochemicals seem to have a specific estrogen-modulating effect, and indole-3-carbinol (I3C) may be the most important phytonutrient in this regard.
Eating broccoli, kale, or other crucifers releases I3C, which is transported to the stomach. I3C is not the only indole formed17 but is probably the most important and well studied.
In the stomach, I3C is converted into many active compounds, one of which is diindolylmethane (DIM). Although DIM appears to be one important metabolite of I3C, most of the past and ongoing studies are performed on I3C itself. This is because I3C breaks down into a number of indole products, aside from DIM, which also may have estrogen-modulating activity.18,19 Cell-culture studies and human clinical trials have shown that I3C at doses of 200–400 mg/day can influence estrogen metabolism and promote formation of 2-OH-estrone, and therefore may be useful in breast cancer prevention.20,21 Current U.S. research studies are under way on I3C and women at increased risk for breast cancer.22
There is some controversy with I3C and when it should be administered. Most studies with I3C suggest it is best used as a preventive agent for women at high risk. Supplementing with I3C after cancer is present is less clear as far as benefit, as animal studies have been conflicting on this issue.23,24
Environmental Effects
Researchers who completed a large study last year concluded that the environment plays a much larger role in cancer development than most people realize. For example, more than 44,000 pairs of twins were assessed for a possible cancer connection in each pair. If inheritance played a major role, there would have been a strong health and disease correlation in both twins, but inherited factors for breast cancer were estimated at 30 percent, at most. Researchers concluded that inherited genetic factors make a minor contribution to cancer susceptibility, and that environmental factors play the principal role.25
The World Health Organization recently reported that breast cancer has become the most common cancer in women throughout the world.26 D. Lindsay Berkson, in Hormone Deception (Contemporary Books, 2000), reports on the accumulation of synthetic molecules in the environment from pesticides, plastics, and a variety of other sources that mimic the effects of the "bad" estrogens and add to cancer risk. Even if a woman doesn't have cancer in her family, with this ever-increasing environmental burden of estrogen-mimicking molecules, she needs to think about cutting her risk: what to do about internal and external environments. There is credible scientific evidence to suggest that consuming certain foods and phytonutrients may have a favorable effect on the risk of estrogen-related cancers.
The Estrogen Dilemma
Dan Lukaczer, N.D., is director of clinical research at the Functional Medicine Research Center, a division of Metagenics International Inc., in Gig Harbor, Wash. Metagenics supplies medical foods and supplements, including those containing lignans, isoflavones, and I3C, to health care practitioners.
References
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"We are conducting a vast toxicological experiment in which our children and our children's children are the experimental subjects." Dr. Herbert Needleman
