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Two Scandinavian studies have provided further evidence that environmental
factors could be affecting men¹s reproductive health.
The studies, published online today (Thursday 28 April) in Europe's leading
reproductive medicine journal Human Reproduction, suggest that environmental
pollutants could be changing the ratio of sperm carrying the X or Y (sex
determining) chromosomes and that they could be contributing towards male
reproductive disorders.
A study by Swedish researchers[1] is the first to show that exposure to
persistent organochlorine pollutants (POPs) can affect the distribution of
sex chromosomes in sperm, leading to a slight increase in the number of
sperm bearing the Y chromosome
Aleksander Giwercman, professor of andrology at the Scanian Andrology
Centre, Fertility Centre, Malmö University Hospital, Lund University,
Sweden, and his colleagues looked at the effect of two POPs (CB-153 and DDE)
on semen in 149 Swedish fishermen, aged between 27 and 67, some of whom
fished off the east coast in the contaminated Baltic Sea, while others
fished off the west coast.
Prof Giwercman explained: ³Closed aquatic ecosystems, such as the Baltic
Sea, have become heavily polluted by POPs. In spite of decreases since the
1970s, this contamination has resulted in higher levels of POPs in humans,
such as fishermen, who consume large quantities of local fatty fish.²
POPs enter the environment in a number of ways. Tarmo Tiido, co-author and
PhD student at the Fertility Centre, said: ³The sources of contamination for
POPs are closely related to human activities such as domestic and industrial
discharge, automobile exhausts, street run-off, slum sewage and agricultural
chemicals. POPs from polluted soils are washed off the land into the sea.
Additionally, the atmosphere plays an important role in their transport over
long distances. POPs have a strong tendency to bioaccumulate in marine and
terrestrial food webs. Humans, being at the top of the food web,
particularly are exposed to POPs.²
The researchers found that larger amounts of both CB-153 and DDE in the
blood of the fishermen was associated with a statistically significant
increase in the proportion of Y chromosome bearing sperm in semen, and that
age, smoking and hormone levels had no effect.
³When we compared the 20% of fishermen with the highest exposure with the
20% with the lowest exposure, DDE was associated with an increase of 1.6% in
sperm with Y chromosomes and CB-153 with an increase of 0.8%. To our
knowledge this is the first study to show that the distribution of the sex
chromosomes in sperm can be affected by exposure to POPs,² said Prof
The study did not enable them to discover whether the increase in Y
chromosome sperm would lead to an increase in boys being born, or what might
be the mechanism involved. ³We need a much larger population in order to
investigate the implications of these changes on sex ratio of offspring as
the number of children born to these fishermen was small.
³However, we think the fact that exposure to environmentally derived
chemicals can change the sex chromosome ratio in sperm is worrying in itself
and requires more attention from scientists and the public,² said Prof
The second study by researchers from Denmark, Lithuania and Finland[2]
suggests that a higher than expected prevalence of cryptorchidism
(undescended testes) in Lithuania could be occurring because changing
environmental factors are affecting the reproductive development of male
Babies born with undescended testes are at higher risk of developing
testicular cancer between the ages of about 20 and 40, and of having
infertility problems. Cryptorchidism is one of the symptoms of testicular
dysgenesis syndrome (TDS) ­ a collection of male reproductive disorders,
possibly caused by errors in development of the foetal testes.
The Lithuanian study investigated 1,204 boys born in one hospital in
Lithuania between October 1996 and November 1997. The boys were examined at
birth and one year later. Sixty-nine (5.7%) of the boys had one or both
testes undescended. After one year the testes had descended fully in 51 of
the 68 children (75%) who were followed up, reducing the overall rate of the
condition from 5.7% to 1.4%.
Dr Niels Jorgensen, one of the authors, said the study was significant
because existing data on male reproductive health in Lithuania showed that
the incidence of testicular cancer was one of the lowest in Europe and that
semen quality in young men was good ­ a similar situation to that in
Finland. ³However, our results showed that the prevalence of cryptorchidism
at birth in Lithuania was 5.7%, which was lower than in Denmark (9%), but
higher than Finland (2.4%). These figures are not consistent with the data
on semen quality and testicular cancer in the Nordic-Baltic region. Based on
these data, we could have expected the frequency of cryptorchidism in
Lithuanian boys to be similar to that in Finnish boys.²

So what could be the reason for the discrepancy between these different
indicators for male reproductive health?
Dr Jorgensen said: ³Recent data show that semen quality and testicular
cancer development is probably determined during the foetal period, but
clinically this is usually not detected until the third decade of life.
Thus, the recent findings of good semen quality and low frequency of
testicular cancer in Lithuania may reflect the intrauterine environment
situation more than 20 years ago. However, cryptorchidism can be detected
immediately after birth and therefore the prevalence of congenital
cryptorchidism detected in this study may be a better reflection of the
current environmental situation than semen quality and the incidence of
testicular cancer.
³If the hypothesis is correct that TDS is caused by environmental
conditions, possibly interacting with genetic factors, the question arises
as to whether adverse changes in the environmental factors affecting male
reproductive health have taken place in Lithuania in the last 20 years.
³We need to look more closely at the role of environmental factors,
including those that can disrupt the hormone system, and the role of
genetics, lifestyle and other factors.²
The study found that cryptorchidism was associated with low birth weight,
preterm delivery, small gestational weight and other congenital
abnormalities of the genitalia. An interesting significant risk factor was
the father¹s weight; babies born to underweight fathers (body mass index
less than 20kg/m2) were six times more likely to have undescended testes.
However, Dr Jorgensen said: ³This finding should be treated with caution
because the number of cases was rather low and only larger studies will be
able to show whether this is a genuine association or not.²
The study did not find a statistically significant difference between boys
born to mothers who smoked or who worked in a potentially harmful
environment where they might be exposed to heat, vibration or chemical, but
the prevalence of cryptorchidism was slightly higher. It rose from 5.1% in
non-smoking mothers to 7.8% in smoking mothers, and from 4.9% to 7.13% for
mothers working in a potentially harmful environment.
³Although this increased risk was not statistically significant, it suggests
that environmental factors could be important,² said Dr Jorgensen.
[1]            Exposure to persistent organochlorine pollutants associates
with human sperm Y:X chromosome ratio. Human Reproduction.
[2]            Higher than expected prevalence of congenital cryptorchidism
in Lithuania: a study of 1204 boys at birth and 1 year follow-up. Human
Reproduction. doi:10.1093/humrep/deh887
1              PDF version of this press release and full embargoed text of
the paper with complete results can be found from 09:00hrs London time
Tuesday 26 April at: or is available from
Emma Mason
2              Human Reproduction is a monthly journal of the European
Society of Human Reproduction and Embryology (ESHRE).

Please acknowledge Human Reproduction as a source.

Dr Helen Beard, Managing Editor. Tel: +44 (0) 1954 212404


3            ESHRE¹s website is:
4            Abstracts of other papers in ESHRE¹s three journals: Human
Reproduction, Molecular Human Reproduction & Human Reproduction Update can
be accessed post embargo from
<>  Full text of papers available on request
from Margaret Willson (Tel: +44 (0)1536 772181. Mobile: +44 (0)7973 85334.



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