Rising rates of breast cancer in women…declining sperm counts in men…girls maturing at ever younger ages…boys born with deformed urinary tracts. Some say these seemingly unrelated trends are part of the mounting evidence that man-made chemicals can impair or amplify the effects of such hormones as estrogen, progesterone, androgen and thyroid hormones.
The suspect substances have been labeled hormone disrupters, endocrine disrupters or pseudohormones because they mimic the body’s natural hormones. It is not entirely understood how they do this, though studies of cells show these substances can attach to receptor sites normally reserved for human hormones.
By doing so, they theoretically can interfere with the body’s hormonal balance, perhaps contributing to certain cancers, birth defects and reproductive abnormalities, suggests Kenneth Korach, Ph.D., of the National Institute of Environmental Health Sciences (NIEHS). Many researchers believe the effects of hormone disrupters may explain, in part, the steady rise in breast cancer, cancers of the testes and prostate, and the decline in men’s sperm counts and quality, as well as the rise in urogenital defects in baby boys. Many other researchers vociferously disagree.
Man-Made vs Natural. Many known hormone disrupters are man-made chemicals, such as pesticides, herbicides, insect repellents, compounds used to make detergents, and byproducts of the manufacture of plastics. Although estimates of the number of such compounds already in the environment go as high as 70,000, Korach says, researchers are only just beginning to screen manufactured compounds for their possible estrogenic effects.
The most widely studied disrupters include dioxin and other chemicals known best by their acronyms: DDT and PCB’s. Although DDT and PCB’s “have been banned for use in the U.S. for many years, they degrade so slowly that the air, the water and the ground still show trace amounts. Moreover, these chemicals continue to be used in many other countries. And most man-made hormone disrupters are stored in body fat (both animal and human), where they can build up over a lifetime.
Other hormone disrupters are estrogens that occur naturally in foods such as soybeans, flaxseed, fruits, vegetables and animal fat. But unlike their synthetic counterparts, these pseudo-strogens or phytoestrogens are not stored in body fat for long periods of time. Thus it is less likely they are harmful to humans, explains Lenore Kohlmeier, Ph.D., of the University of Noah Carolina School of Public Health. “Several studies show that phytoestrogens are actually protective against certain diseases,” she says. Some experts think these natural hormone disrupters may be protective because they compete with synthetic hormone disrupters for the same receptor sites on cells. Overall, however, the research in this area has been inconclusive.
Important or Inconsequential? The question that remains to be answered is: Does everyday, low-dose exposure to pesticides and other environmental pollutants with hormonal properties pose a health risk?
“There are two main schools of thought,” says NIEHS’s Korach. “One believes there’s no concern because there’s no [evidence from population studies] to support the belief that environmental estrogens pose a health risk. The other looks at wildlife exposure and animal studies and believes they are just a tip-off to what can happen in humans.”
Several animal studies and limited population studies provide evidence that hormone disrupters can be dangerous. Wildlife exposed to high levels of estrogenic pesticides have suffered reproductive problems such as infertility and genital malformations. Off-spring of adult animals exposed to these chemicals were severely affected, developing numerous urogenital defects, infertility and other health problems.
What about evidence in humans? Laboratory studies of human cancer cells show exposure to certain estrogenic chemicals can stimulate tumor cell growth. But clinical studies have generally found effects in humans only at very high levels of exposure, such as in the children of workers who apply pesticides to crops.
Are hormone disrupters to blame for the rise in breast cancer rates? Despite much conjecture, published research so far suggests no. An extensive review of the research recently concluded there appears to be no effect from exposure to DDT and PCB’s on breast cancer risk. “If anything,” says University of North Carolina’s Kohlmeier, “the data suggests they may slightly protect against breast cancer.”
That’s not as far-fetched as it sounds, since natural phytoestrogens in soy have been touted for the same thing. Many studies have suggested that the large amounts of soy consumed by Asians protects them against breast cancer. Animal and test tube research reveals the phytoestrogens in soy compete with harmful estrogens that promote the growth of certain tumors.
But other researchers believe it’s too early to rule out the theory that some hormone disrupters may contribute to breast cancer in some women. “There are eight to 10 studies looking at this issue now,” says Gwen Collman, Ph.D., of Environmental Epidemiology at the NEIHS. She explains there may be a group of women with a particular genetic defect that makes them sensitive to low-dose exposure to hormone disrupters.
The Bottom Line. Research in this field is still in its infancy, so it’s far too early to tell who’s right in this debate. But we may have more answers in the next five years, because a White House scientific panel recently declared hormone disrupters a national health priority and allocated millions of dollars for research.
For now, there is little concrete evidence that low-dose exposure to hormone disrupters will cause you harm. Yet to be prudent, and within practical reason, you may want to limit your exposure to known man-made hormone disrupters. Here’s how:
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