[Pharmwaste] Trends in disease don't always reveal environmental
Deborah.DeBiasi at deq.virginia.gov
Fri Jul 24 11:32:32 EDT 2009
Trends in disease don't always reveal environmental causes
Scientific evidence has demonstrated that a cluster of male
disorders-testicular cancers, poor semen quality, undescended testicles
and hypospadias-have common origins, and that environmental chemicals
might play a role. At the same time, some studies have shown that these
diseases and disorders are not increasing across all populations and
regions. Is this a contradiction? To scientists, no.
By Shanna Swan
University of Rochester
July 24, 2009
An increasingly convincing body of evidence has demonstrated that a
cluster of male disorders-testicular cancers, poor semen quality,
undescended testicles and hypospadias-have common origins, and that
environmental chemicals might play a role.
At the same time, some studies have shown that these diseases and
disorders are not increasing across all populations and regions of the
Is this a contradiction?
To scientists, no.
Many people think that if there is an environmental cause, then illness
rates must be going up everywhere. For example, if an air pollutant
causes cancer, then why isn't cancer increasing in all polluted cities?
But in fact, local trend studies seldom provide evidence to refute or
support causes of human disease.
On rare occasions, there is compelling data on changes in disease and
exposure over time that strongly support a cause and effect
relationship. For example, the pattern of sales of diethylstilbestrol
(DES), a drug marketed between 1947 and 1971 to prevent miscarriage,
showed a remarkable link to the number of cases of a rare vaginal cancer
diagnosed in the "DES daughters" twenty years later. Overwhelming
evidence that this unique cancer was rarely, if ever, seen in young
women prior to the sale of DES argues very convincingly that the
exposure caused the diseases. In fact, no other cause of this cancer in
young women has ever been identified.
This, however, is an exception. Why? First, diagnoses of most diseases
can change over time, and most are likely to be incompletely reported in
disease registries. For these reasons alone, disease rates can change
over time even when there has been no change in the factors that cause
Unlike the rare cancer caused by DES in young women, diseases and other
adverse outcomes, such as hypospadias, almost always have multiple
causes. These causes can also change over time. For example, researchers
have noted in two recent papers that this malformation in male newborns
increases with maternal age. And maternal age at birth has itself been
increasing as women postpone childbearing. Risk of hypospadias has been
linked to other environmental factors, including anti-androgens such as
the phthalate diethylhexyl phthalate (DEHP), which is present in food
and many vinyl products. All of these factors are subject to their own
In one recent study, the authors controlled for maternal age in their
analysis of 921,745 Danish births and reported that the rate of
hypospadias increased between 1977 and 2005. Another examined younger
and older mothers separately and saw no increase based on New York State
registry cases between 1983 and 2005. But neither of these studies can
provide evidence either for or against the hypothesis that DEHP or other
environmental risk factors are related to these trends. Why? First,
unlike the data about the sales of the miscarriage drug, we have no
reliable data about the changes in production or distribution of
environmental chemicals, such as DEHP. While it is highly likely that
exposure to DEHP is higher now than 50 years ago, we have no data with
which to compare current exposures to those in the more recent past.
They could have increased, decreased or remained constant. Moreover,
exposure patterns are unlikely to have been uniform globally.
So can scientists ever link environmental chemicals to disease? Yes.
Studies that utilize data on individual exposure are far more useful
than simply looking at trends. For example, one recent study found that
occupational phthalate exposure was associated with a three-fold
elevated risk of hypospadias.
Such studies can help identify the role played by environmental
chemicals in complex disease. Trend studies alone cannot.
Shanna Swan is Professor and Associate Chair for Research at the Dept.
of Obstetrics and Gynecology and
Director of the Center for Reproductive Epidemiology at the University
of Rochester School of Medicine and Dentistry.
She can be reached at shanna_swan at urmc.rochester.edu
Deborah L. DeBiasi
Email: Deborah.DeBiasi at deq.virginia.gov (NEW!)
WEB site address: www.deq.virginia.gov
Virginia Department of Environmental Quality
Office of Water Permit Programs
Industrial Pretreatment/Toxics Management Program
PPCPs, EDCs, and Microconstituents
Mail: P.O. Box 1105, Richmond, VA 23218 (NEW!)
Location: 629 E. Main Street, Richmond, VA 23219
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