Endocrine Disruptors
A growing body of evidence suggests that
numerous chemicals, both natural and man-
made, may interfere with the endocrine
system and produce adverse effects in
laboratory animals, wildlife, and humans.
Scientists often refer to these chemicals as
“endocrine disruptors.” Endocrine disruption
is an important public health concern that is
being addressed by the National Institute of
Environmental Health Sciences (NIEHS).
These chemicals are found in many of the
everyday products we use, including some
plastic bottles and containers, liners of metal
food cans, detergents, flame retardants, food,
toys, cosmetics, and pesticides. Although
limited scientific information is available on
the potential adverse human health effects,
concern arises because endocrine disrupting
chemicals present in the environment at
very low levels have been shown to have
adverse effects in wildlife species as well as in
laboratory animals. The difficulty of assessing
public health effects is increased by the fact
that people are typically exposed to multiple
endocrine disruptors simultaneously.
NIEHS and the National Toxicology Program
(NTP) support research to understand how
these chemicals work, and to understand the
effects they may have in various animal and
human populations, with the long term goal
of developing prevention and intervention
strategies to reduce any adverse effects.
What are endocrine disruptors?
Endocrine disruptors are naturally occurring
compounds or man-made substances that may mimic
or interfere with the function of hormones in the
body. Endocrine disruptors may turn on, shut off,
or modify signals that hormones carry, which may
affect the normal functions of tissues and organs.
Many of these substances have been linked with
developmental, reproductive, neural, immune, and
other problems in wildlife and laboratory animals.
Some research suggests that these substances are also
adversely affecting human health in similar ways,
resulting in reduced fertility and increased incidences
or progression of some diseases, including obesity,
diabetes, endometriosis, and some cancers.
These chemicals have also been referred to as
endocrine modulators, environmental hormones,
and endocrine active compounds. Environmental
chemicals with estrogenic activity are probably the
most well studied, however chemicals with anti-
estrogen, androgen, anti-androgen, progesterone,
or thyroid-like activity have also been identified.
The endocrine system keeps our bodies
in balance, maintaining homoestasis and
guiding proper growth and development.
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What is the endocrine system and why is it important?
The endocrine system is one of the body’s main
communication networks and is responsible for
controlling and coordinating numerous body
functions. Hormones are first produced by the
endocrine tissues, such as the ovaries, testes, adrenal,
pituitary, thyroid, and pancreas, and then secreted into
the blood to act as the body’s chemical messengers
where they direct communication and coordination
among other tissues throughout the body.
For example, hormones work with the nervous
system, reproductive system, kidneys, gut, liver,
and fat to help maintain and control:
• Body energy levels
• Reproduction
• Growth and development
• Internal balance of body systems, or homeostasis
• Response to surroundings, stress, and injury
Endocrine disrupting chemicals may interfere with
the body’s own hormone signals because of their
structure and activity.
How are people exposed to endocrine disruptors?
People may be exposed to endocrine disruptors
through the food and beverages they consume,
medicine they take, pesticides they apply, and
cosmetics they use. So, exposures may be through
the diet, air, skin, and water.
Some environmental endocrine disrupting
chemicals, such as the pesticide DDT, dioxins, and
polychlorinated biphenyls (PCBs) used in electrical
equipment, are highly persistent and slow to
degrade in the environment making them potentially
hazardous over an extended period of time.
What is NIEHS research telling us about
endocrine disruptors?
NIEHS has been a pioneer in conducting research
on the health effects of endocrine disruptors
for more than three decades, starting with the
endocrine-disrupting effects of the pharmaceutical,
diethylstilbestrol (DES).
From the 1940s–1970s, DES was used to treat women
with high-risk pregnancies, with the mistaken belief
that it prevented miscarriage. In 1972, prenatal
exposure to DES was linked to the development of
a rare form of vaginal cancer in daughters whose
mother received DES, and with numerous non-
cancerous changes in both sons and daughters.
NIEHS researchers developed animal models of
DES exposure that successfully replicated and
predicted human health problems, and have been
useful in studying the mechanisms involved in DES
toxic effects.1 NIEHS researchers also showed that
the effects of DES and other endocrine disruptors
involved the estrogen receptor.2
In addition to the fact that we now know that
endocrine disruptors are widely dispersed in our
environment, some other key points about exposure
to endocrine disruptors have emerged.
Exposures at low levels count.
The body’s own normal endocrine signaling involves
very small changes in hormone levels, yet we know
these changes can have significant biological effects.
This leads scientists to think that chemical exposures,
even at low doses, can disrupt the body’s delicate
endocrine system and lead to disease.
In 2000, an independent panel of experts convened
by NIEHS and NTP found that there was “credible
evidence” that some hormone-like chemicals can
affect test animals’ bodily functions at very low levels
— well below the “no effect” levels determined by
traditional testing.3
Four points about endocrine disruption:
• Low dose matters
• Wide range of health effects
• Persistence of biological effects
• Ubiquitous exposure