What could be the effects on humans?
Little is known about the possible effects
of hormone disrupting chemicals on humans. Most of the evidence
for hormone disrupting toxicity has come from studies on animals
or on cell cultures, including human cell culture. There is little
data available on human effects, partly because of the unacceptability
of doing deliberate experiments on humans. However, there are
some worrying trends in the health of both men and women.
Worrying trends in male health
Testicular cancer has increased in incidence
by 55 per cent between 1979 and 1991 in England and Wales; there
were 1137 new cases of testicular cancer in 1991 (Cancer Research
Campaign Data, January 1998). Testicular cancer is believed to
result mainly from problems occurring during the development
of testes whilst the individual is developing in their mother's
womb, and hormone disrupting chemicals are hypothesised to be
a cause of the increase (Skakkebaek et al, 1998).
Since testicular cancer is mainly a disease
of young men, the increased age of the population is not a reason
for the increase of this cancer (as it is with many other cancers).
Rates of increase measured in other countries include: an increase
of 300% between 1945 and 1990 in Denmark and an annual increase
of 2.3% in the Baltic countries (IEH, 1995). It is clear that
rates of increase and incidence vary between different countries,
with Finland having among the lowest incidence in Europe; men
in Finland also seem to have the highest sperm counts in Europe
(Jensen et al., 1995).
It is thought that testicular cancer is
initiated early in life, before birth (see the endocrine
system page for more information).
Many studies in recent years have suggested
that sperm counts have reduced in the last 40 or so years. A
major re-analysis of results from many studies concluded that
sperm counts in Europe and the USA have been declining, with
sperm counts in Europe having declined at 3.1 million/ml/yr over
the period 1971-1990 (Swann et al., 1997). One of the authors
of this study summarises her most recent research on the ECME
One of the worrying trends to show up in
some studies is a correlation between the year of birth and the
sperm count, with those born most recently having the lowest
sperm counts (Lancet, 1995). A study of the sperm counts of Scottish
men has shown that men born in the 1970s are producing 24 % fewer
sperm than are men born in the 1950s (Irvine et al., 1996). However,
a smaller study published at the same time suggests that sperm
count has not declined in specimens collected in Toulouse, France
between 1977 and 1992. This is in contrast to earlier research
in Paris which did show a fall; the authors suggest that this
difference may be due to environmental differences (Bujan et
The reproductive abnormalities cryptorchidism
(undescended testes) and hypospadias (urethra opening on the
underside of the penis) may also be increasing, but the data
on cryptorchidism is very limited, and on hypospadias there are
problems of definition (IEH, 1995). However, clear increases
in cryptorchidism have been observed in England, and increases
in incidence of hypospadias have been observed in many countries
(Jensen, 1995). The incidence of hypospadias in Finland is lower
than in other Scandinavian countries (Jensen, 1995).
Reducing proportion of male babies?
The ratio of male to female births has
declined during the last 20-40 years in Denmark, the Netherlands,
Sweden, Germany, Norway, Finland, Canada and the US, so fewer
male babies are being born than would normally be expected. It
is not clear why this is happening, though environmental pollution
and hormone disrupting chemicals have been suggested as possible
causes. This hypothesis is supported by data from Seveso, Italy,
where an industrial accident released large amounts of dioxin
(see below). In the eight years after the accident 12 daughters
and no sons were born to nine couples with the highest dioxin
exposure (Davis et al, 1998; Raloff, 1998).
Worrying trends in the health of women
Breast cancer has been estimated to have
increased in incidence by one per cent per year since the 1940s
in the USA, and has increased by 50 per cent in Denmark between
1945 and 1980 (IEH, 1995). It has also increased in incidence
in the UK over the last few decades. Research has suggested a
link between breast cancer and exposure to hormone disrupting
chemicals such as DDT, dioxin and PCBs
(Wolf et al., 1997).
Research is suggesting that girls in the
US are now entering puberty earlier than has been found by studies
in the past (Herman-Giddens et al., 1997). The potential role
of chemicals in this change is supported by a study which compared
the onset of puberty in children with the levels of two persistent
synthetic chemicals, PCBs and DDE in their mothers whilst they
were pregnant. Girls whose mothers had the highest levels, and
who were therefore exposed to the highest amounts of DDE and
PCBs in the womb, entered puberty 11 months earlier than girls
with lower exposures. The onset of puberty in boys was not affected.
Other studies have shown that girls who enter puberty earlier
are at increased risk of breast cancer (Boyce, 1997).
This page was last
updated in October 1999
to the hormone disrupting chemicals home page
Boyce, N. 1997. Growing up too soon. New
Scientist 2nd August, p5.
Bujan, L., Mansat, A., Pontonnier, F. and
Mieusset, R. 1996. Time series analysis of sperm concentration
in fertile men in Toulouse, France between 1977 and 1992. British
Medical Journal 312: 471-472.
Davis, D. L., Gottlieb, M. B. and Stampnitzky,
J. R. 1998. Reduced ratio of male to female births in several
industrial countries: A sentinel health indicator? Journal
of the American Medical Association 279, p1018-1023
Herman-Giddens, M. E., Slora, E. J., Wasserman,
R. C., Bourdony, C. J., Bhapkar, M. V., Koch, G. G. and Hasemeier,
C. M. 1997. Secondary sexual characteristics and menses in young
girls seen in office practice: A study from the pediatric research
in office settings network. Pediatrics 99, p505-512.
IEH 1995. Environmental oestrogens: Consequences
to human health and wildlife. Institute for Environment and Health,
University of Leicester, Leicester, UK
Irvine, S., Cawood, E., Richardson, D.,
MacDonald, E. and Aitken, J. 1996. Evidence of deteriorating semen
quality in the United Kingdom: birth cohort study in 577 men in
Scotland over 11 years. British Medical Journal 312: 467-471.
Jensen, T.K., Toppari, J., Keiding, N.,
Skakkebaek, N.E. 1995. Do environmental estrogens contribute to
the decline in male reproductive health?. Clinical Chemistry 41:
Lancet 1995. Editorial: Male reproductive
health and environmental oestrogens. The Lancet 345: 933-935.
Raloff, J. 1998. Why are boys' birth rates
falling? Science News Online (www.sciencenews.org) 4/4/98.
Skakkebaek, N. E., Rajpert-De Meyts, R.,
Jørgensen, N., Carlsen, E., Peterson, P. M., Giwercman,
A., Andersen, A.-G., Jensen, T. K., Andersson, A.-M. and Müller,
J. 1998. Germ cell cancer and disorders of spermatogenesis: An
environmental connection? APMIS 106, p3-12.
Swann, S. H., Elkin, E. P. and Fenster,
L. 1997. Have sperm densities declined? A reanalysis of global
trend data. Environ. Health Persp. 105: 1228-1232.
Wolff, M. S. and Weston, A., 1997. Breast
cancer risk and environmental exposures. Environmental Health
Perspectives 105, p891-896.