Over the past decade, a growing shown to have adverse effects Some scientists think these
body of evidence suggests in wildlife species, as well as chemicals also are adversely
that numerous chemicals, in laboratory animals at these affecting human health in
both natural and man-made, low levels. similar ways resulting in
may interfere with the endocrine The difﬁculty of assessing public declined fertility and increased
system and produce adverse health effects is increased by incidences or progression of
effects in humans, wildlife, the fact that people are typically some diseases including
ﬁsh or birds. Scientists often exposed to multiple endocrine endometriosis and cancers.
refer to these chemicals as disruptors simultaneously. These chemicals have also
“endocrine disruptors.” The National Institute of been referred to as endocrine
These chemicals are found in Environmental Health Sciences modulators, environmental
many of the everyday products (NIEHS) and the National hormones, and endocrine active
we use including some plastic Toxicology Program (NTP) compounds. Environmental
bottles, metal food cans, support research to understand chemicals with estrogenic
how these chemicals work activity are probably the most
and to understand the effects well studied however chemicals
that they may have in various with anti-estrogen, androgen,
animal and human populations anti-androgen, progesterone,
with the long term goals of or thyroid-like activity have also
developing prevention and been identiﬁed.
intervention strategies to reduce
any adverse effects. What is the Endocrine System
and Why is it Important?
What are Endocrine Disruptors?
The endocrine system is one of
Endocrine disruptors are the body’s main communication
naturally occurring compounds networks and is responsible for
or man-made chemicals that controlling and coordinating
detergents, ﬂame retardants, may interfere with the numerous body functions.
food, toys, cosmetics, and production or activity of Hormones are ﬁrst produced
pesticides. Although limited hormones of the endocrine by the endocrine tissues, such
scientiﬁc information is system leading to adverse as the ovaries, testes, pituitary,
available on the potential health effects. Many of thyroid and pancreas, and then
adverse human health effects, these chemicals have been secreted into the blood to act as
concern arises because endocrine linked with developmental, the body’s chemical messengers
disrupting chemicals while reproductive, neural, immune, where they direct communication
present in the environment at and other problems in wildlife and coordination among other
very low levels, have been and laboratory animals. tissues throughout the body.
PO BOX 12233
Research Triangle Park, NC 27709
For example, hormones work How do Endocrine such as Bisphenol A are
with the nervous system, Disruptors work? suspected endocrine disruptors
reproductive system, kidneys, From animal studies, researchers based on animal studies.
gut, liver and fat to help have learned much about the Bisphenol A (BPA) is a man-
maintain and control: mechanisms through which made chemical that can leach
• body energy levels endocrine disruptors inﬂuence out of plastic products when
• reproduction the endocrine system and alter heated. BPA is used in the
hormonal functions. manufacture of polycarbonate
• growth and development
plastics, often used for food and
• internal balance of body Endocrine disruptors can:
beverage containers, and epoxy
systems, called homeostasis • mimic or partly mimic naturally resins found in dental sealants.
• responses to surroundings, occurring hormones in the
body like estrogens (the female Bisphenol A (BPA)
stress, and injury
sex hormone) and androgens
Endocrine disrupting chemicals (the male sex hormone) and
may interfere with the body’s thyroid hormones, potentially
own hormone signals because producing overstimulation OH OH
of their structure and activity.
• bind to a receptor within a Some endocrine disruptors
cell and block the endogenous occur among a group of
hormone from binding. chemicals referred to as
Hormone The normal signal then fails phthalates, a class of chemicals
Receptor that soften and increase the
to occur and the body fails to
respond properly. Examples ﬂexibility of polyvinyl chloride
of chemicals that block or plastics. An example of a
antagonize hormones are anti- phthalate is a compound called
estrogens or anti-androgens. Di (2-ethylhexyl) phthalate
Nucleus (DEHP). DEHP is a high
• interfere or block the way
production volume chemical
natural hormones or their
Hormone used in the manufacture of
Mimic receptors are made or
a wide variety of consumer
controlled, for example by
products, such as building
blocking their metabolism
products, car products, clothing,
in the liver.
food packaging, some children’s
What are some examples products and some polyvinyl
of Endocrine Disruptors? chloride medical devices.
Recently, an independent panel
A wide and varied range of of experts assembled by the
substances are thought to National Toxicology Program
Hormone cause endocrine disruption. (NTP) found that DEHP
Blocker Chemicals that are known may pose a risk to human
endocrine disruptors include development, especially for
diethylstilbesterol (the drug critically ill male infants.1
DES), dioxin and dioxin like
compounds, PCBs, DDT, Phytoestrogens are naturally
and some other pesticides. occurring substances in plants
Some chemicals, particularly that have hormone-like activity.
pesticides and plasticizers, Examples of phytoestrogens
are genistein and daidzein disruptors for more than • Conducting epidemiological
which can be found in soy three decades starting with studies in human populations
derived products. the endocrine disrupting • Developing new assessment
effects of the pharmaceutical and biomarkers to determine
To speciﬁcally evaluate the
effects that chemicals have diethylstilbestrol (DES). exposure and toxicity levels,
on human reproduction, the From the 1940s -1970s, DES was especially how mixtures of
National Toxicology Program used to treat women with high chemicals impact individuals
(NTP) developed The Center risk pregnancies with the
• Developing intervention and
for the Evaluation of Risks to mistaken belief that it prevented
Human Reproduction (CERHR). miscarriage. In 1972, prenatal
This center has evaluated the exposure to DES was linked Some examples of ﬁndings in
endocrine disruptor effects with the development of a rare important research areas are
of seven phthalates and the form of vaginal cancer in the provided below.
phytoestrogen genistein found DES-daughters, and with
in soy infant formulas.2 numerous non-cancerous
changes in both sons and Research shows that endocrine
How are People Exposed to daughters. NIEHS researchers disruptors may pose the
Endocrine Disruptors? greatest risk during prenatal
developed animal models of
People may be exposed to DES exposure that successfully and early postnatal development
endocrine disruptors through replicated and predicted human when organ and neural systems
the food and beverages they health problems and have are developing. In animals,
consume, medicine they take, been useful in studying the adverse consequences, such
and cosmetics they use. mechanisms involved in DES- as subfertility, premature
toxic effects.3 NIEHS researchers reproductive senescence and
also showed the effects of DES cancer are linked to early
and other endocrine disruptors exposure, but they may not
involved the estrogen receptor be apparent until much later
protein mechanism.4 Researchers in life.5
are playing a lead role in Researchers supported by
uncovering the mechanisms of NIEHS at the University of
action of endocrine disruptors Cincinnati and the University
of Illinois found that animals
So, exposures may be Today, scientists are: exposed to low doses of the
through the diet, air, and skin.
• Developing new models and natural human estrogen
Some environmental endocrine
tools to better understand how estradiol, or the environmental
disrupting chemicals, such as
endocrine disruptors work estrogen bisphenol A (BPA),
DDT, are highly persistent
during fetal development and
and slow to degrade in the • Developing high throughput estradiol as adults were more
environment making them assays to determine which likely to develop a precursor of
potentially hazardous over chemicals have endocrine prostate cancer than those who
an extended period of time. disrupting activity were not exposed. This suggests
What Is NIEHS Research • Examining the long-term that exposure to environmental
Telling Us About effects of exposure to and natural estrogens during
Endocrine Disruptors? various endocrine disrupting fetal development could affect
The NIEHS has been a pioneer compounds during the way prostate genes behave,
in conducting research on the development, and on disease and may lead to higher rates of
health effects of endocrine and dysfunction later in life prostate disease during aging.6
Exposures at Low Levels disrupting agents to have New research funded by the
effects on other endocrine NIEHS also found that endocrine
In 2000, an independent panel of
systems not yet fully examined. disruptors may affect not just
experts convened by the NIEHS
Transgenerational Effects the offspring of mothers
and the National Toxicology
exposed during pregnancy,
Program (NTP) found that there There is some evidence that but future offspring as well.
was “credible evidence” that endocrine disruptors may The researchers found that two
some hormone-like chemicals not only impact the individual endocrine disrupting chemicals,
can affect test animals’ bodily directly exposed, but also caused fertility defects in male
functions at very low levels - future generations. rats that were passed down to
well below the “no effect”
Research from NIEHS nearly every male in subsequent
levels determined by traditional
investigators have shown generations. This study suggests
testing.7 Although, there is little
that the adverse effects of that the two compounds may
evidence to prove that low-dose
DES in mice can be passed to have caused changes in the
exposures are causing adverse
subsequent generations even developing male germ cells
human health effects, there
though they were not directly and that endocrine disruptors
is a large body of research in
exposed. The increased may be able to reprogram or
experimental animals and
susceptibility for tumors was change the expression of genes
wildlife suggesting that endocrine
seen in both the granddaughters without mutating DNA.10
disruptors may cause:
and grandsons of mice who The role of environmental
• reductions in male fertility were developmentally exposed endocrine disrupting chemicals
and declines in the numbers to DES.8 Mechanisms involved in the transmission of disease
of males born in the transmission of disease from one generation to another
• abnormalities in male were shown to involve is of great research interest to
reproductive organs epigenetic events.9 the NIEHS.
• female reproductive diseases
including fertility problems,
early puberty, and early
• increases in mammary,
ovarian, and prostate cancers
There are data showing that
exposure to Bisphenol A
as well as other endocrine
disrupting chemicals with
estrogenic activity may have
effects on obesity and diabetes.
These data while preliminary
and only in animals indicate
the potential for endocrine
NTP Brief on the Potential Human Reproductive and Developmental Effects of Di (2-ethylhexyl) Phthalate (DEHP). Draft, May 2006.
Endocrinology 147 (6) Supplement S11-S17, 2006.
Developmental Biology. 2001. 238:224-238.
Environmental Health Perspectives 103:83-87, 1995. Endocrinology 147 (6) Supplement S11-S17, 2006.
Cancer Research. 2006 Jun 1;66(11):5624-32.
National Toxicology Program’s Report of the Endocrine Disruptors Low-Dose Peer Review, 2001.
Carcinogenesis. 2000 Jul;21(7):1355-63. Carcinogenesis 19; 1655-1663.
Cancer Research 2000 60-235-237.
Science 3 June 20. Vol. 308. no. 5727, pp. 1466 - 1469.