Another Enviro-Scare Debunked
By Stephen Safe
Copyright 1999 Wall Street Journal
August 20, 1997
It was one of the big health scares of the '90s.
"The Estrogen Complex," Newsweek dubbed it in 1994: "Sperm counts
down, [animal] penises shriveled... It may be from chemical pollutants in water
and food." "Environmental estrogens," found in pesticides and
other industrial chemicals, were blamed for both reducing men's sperm counts and
increasing women's risk of breast cancer. Last year's book "Our Stolen
Future," which pushed that thesis, created quite a media splash.
Lawmakers responded: In a pair of 1996 laws, the
Safe Drinking Water Act and the Food Quality Protection Act, Congress mandated
that the Environmental Protection Agency develop screening and testing
guidelines for endocrine disruptors, the chemical family that includes
estrogens. But new evidence raises serious questions about the hypotheses on
which these laws are based.
Endocrine systems in humans and animals are
highly regulated signaling pathways in which specific hormones, such as
estrogens, are synthesized and delivered to various target tissues, where they
bind hormone receptors and trigger a wide range of responses. Endogenous
estrogens (those produced by the body itself) are necessary for the development
of the female reproductive tract and secondary sex organs, and are also
important in maintaining the integrity of the bone structure and cardiovascular
systems. They may also influence brain degeneration and Alzheimer's disease.
A woman's lifetime exposure to estrogens is the
most well-characterized risk factor for both breast and endometrial cancer.
Moreover, both sons and daughters of women who took the potent estrogenic drug
diethylstilbestrol (DES) during pregnancy exhibit high incidences of some
serious health problems.
The Press's Ignominious Role
The current scientific and regulatory focus on
environmental estrogens--also called xenoestrogens--and other hormonally active
chemicals was based in part on the experience with DES. Recent reports raised
scientific concerns about the potential global threat of endocrine disruptors on
human health. In 1992 a group from the University of Copenhagen published a
paper that analyzed 61 sperm-count studies from laboratories around the world
and concluded "that sperm density has declined appreciably during
1938-1990"--by more than 40%. Soon after, the British journal Lancet
published an article hypothesizing that a world-wide decline in male
reproductive capacity may be related to exposure to estrogens and other
endocrine disruptors. At about the same time, two studies on a small number of
breast cancer patients in the northeastern U.S. reported higher levels of
organochlorine pollutants (PCBs or DDE) in the patients than in a control group
of women not suffering from breast cancer. It was hypothesized that estrogenic
pollutants may contribute to the increased incidence of breast cancer.
One of the most intriguing studies was a paper by
scientists at Tulane University in New Orleans. They reported in the June 1996
issue of Science that mixtures of some weakly estrogenic chemicals were up to
1,600 times more active than the compounds alone. These reports, coupled with
research showing that exposure to various endocrine-disrupting pollutants was
associated with reproductive problems in wildlife--including decreased penis
sizes in alligators living in a contaminated Florida lake--galvanized scientific
and public concern about environmental estrogen.
But some scientists--including me--were
skeptical. We pointed out that the human diet contains significant quantities of
estrogenic chemicals--including phytoestrogens in fruits, vegetables and nuts,
which have generally been associated with health benefits, including protection
from some hormone-related cancers. Estrogenic hormones are used with great
success by millions of postmenopausal women as hormone-replacement therapy, and
the antiestrogenic compound tamoxifen is used as the first line of defense for
the treatment of women with breast cancer. Moreover, birth-control pills and
several other hormonally active drugs are used for treating prostate cancer and
other diseases. The dietary intake of natural estrogenic compounds in various
foods and estrogenic drugs used in pharmaceuticals far outweighs exposure to
trace dietary levels of xenoestrogens.
The sperm-count issue has been hotly debated and
intensively investigated since the appearance of the 1992 paper. Reports from
France, Belgium and Sweden also showed declining sperm counts from donors in
local clinics over a period of 20 to 25 years. But other recent studies have
shown that over the same period sperm counts in California, Minnesota, New York,
Washington state, Finland and Toulouse, France, were unchanged.
Last summer, Per Emil Rasmussen of Denmark's
Odense University Hospital presented a scientific paper which showed that from
1993 to 1995, the average sperm count at the Odense clinic was 144 million sperm
per milliliter of semen -- significantly higher than the 70 million per
milliliter observed in Copenhagen (which formed part of the basis for the
initial scare). Other recent studies demonstrate clearly that there are
remarkable regional differences in sperm counts. Harry Fisch and his colleagues
at New York's Columbia-Presbyterian Medical Center reported that average sperm
counts in New York, Minneapolis and Los Angeles were 131.5 million, 100.8
million and 72.7 million per milliliter, respectively. These levels remained
constant from 1970 to 1994.
The causes of these regional differences are
unknown and require further study. But it is unlikely that they are related to
environmental estrogens and related contaminants, since levels of these
compounds in humans, wildlife and foods are similar in most regions, and some
have been declining.
Two recent studies also cast doubt on the
hypothesis that xenoestrogens are a cause of breast cancer. A 1994 study of 150
breast cancer patients and 150 control subjects in California reported that
there were no significant differences in serum PCB and DDE levels in either
group. And a study that appeared last month in the British Medical Journal
reported that DDE levels in 265 postmenopausal women with breast cancer and 341
control subjects were not significantly different. Genetics, diet and a woman's
lifetime exposure to estrogens are the major known risk factors for breast
cancer; no causal association between environmental chemicals and the disease
has been demonstrated.
What about the Tulane study published in Science
that so concerned the press? Subsequent work in several other laboratories
failed to produce any evidence of the effects the study had hypothesized. In the
July 25, 1997, issue of Science, the Tulane scientists formally withdrew their
original paper, acknowledging that they "have not been able to replicate
our initial results."
There are still claims that xenoestrogens and
other environmental compounds may affect the immune system and neurodevelopment
in children; these are being investigated and no conclusions have been reached
yet. However, it is clear that the best science now points to the conclusion
that xenoestrogens and related compounds are less harmful than had been
suggested. Which raises two questions: In light of the new findings, will
Congress reconsider the laws it passed last year? And will newspapers and
magazines pay as much attention to scientific news that isn't alarming?
Mr. Safe is a professor of toxicology at Texas