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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

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).

Sperm counts

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 site here.

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 al., 1996).

Reproductive abnormalities

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

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).

Early puberty

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
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References

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: 1896-1901.

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.


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