One
in three “non-toxic” chemicals used in the manufacture of everyday items
significantly affected the potency of sperm cells, which may account for the
high incidence of unexplained infertility in the human population, the
researchers said.
It
is the first time that a study has found a direct effect of the many ubiquitous
man‑made chemicals in the environment on a vital function of human sperm. The
findings will raise further concerns about the hidden toxicity of chemicals
deemed safe by toxicology tests.
But
the researchers believe they have developed a new way of testing the impact of
household chemicals on human sperm which will allow regulatory authorities in
Europe to decide whether to ban or impose restrictions on their use in certain
products.
The
study was part of wider research into so-called “endocrine‑disrupting” chemicals
that for several years have been linked with declining sperm counts and
widespread male infertility.
In
some cases, these chemicals are thought to mimic female sex hormones –
oestrogens – and in other cases act as anti-androgens, the male sex hormones,
thereby interfering with the male reproductive system.
However,
the scientists found that one in three common household chemicals found in
products such as sun screens, detergents and plastics directly sabotaged the
human sperm’s swimming behaviour and caused them to prematurely release the
critical enzymes needed to penetrate and fertilise the egg cell – which would
render the sperm infertile.
They
also found that the concentrations needed to trigger these adverse reactions
were similar to the very low levels commonly found within the human body. In
addition, they showed for the first time that there was a “cocktail effect”,
when a number of chemicals worked together to amplify their individual
effects.
“For
the first time, we have shown a direct link between exposure to
endocrine-disrupting chemicals from industrial products and adverse effects on
human sperm function,” Professor Niels Skakkebaek, of Copenhagen University
Hospital in Denmark, said.
“In
my opinion, our findings are clearly of concern as some endocrine-disrupting
chemicals are possibly more dangerous than previously thought. However, it
remains to be seen from forthcoming clinical studies whether our findings may
explain reduced couple fertility which is very common in modern societies,”
Professor Skakkebaek told The Independent.
Professor
Skakkebaek has pioneered the scientific investigation of rising male
infertility. In 1991, he produced the first evidence showing that human sperm
counts had fallen by nearly 50 per cent in less than 50 years – low sperm counts
are a major cause of male infertility.
Some
years later, scientists found that some common chemicals have an “oestrogenic”
or “antiandrogenic” effect on the male reproductive system, which could be
particularly important in the development of male foetuses in the womb during
the critical first six months when the reproductive tissues form.
However,
the latest research, published in EMBO reports and carried out with Timo
Strünker of the Centre of Advanced European Studies and Research in Bonn,
Germany, found that 30 out of 96 common household chemicals had a direct effect
on the “catsper” protein which controls the sperm cell’s motility, or swimming
agility, and its ability to enter the egg cell to trigger fertilisation.
“We
have found a completely novel way in which endocrine-disrupting chemicals may
affect human reproduction by direct interaction with human sperm,” Professor
Skakkebaek said.
Relatively
low concentrations of the chemicals – which previously were thought to be too
low to cause an effect – triggered the catsper reaction in test-tube
studies.
“In
human body fluids, one does not find one of a few particular chemicals, but
rather complex chemical cocktails with many different endocrine-disrupting
chemicals at very low concentrations. We tried to mimic this situation in our
experiments,” Dr Strünker said. “When mixed together the cocktail, despite the
extremely low concentration of its ingredients, evoked large and sizeable
responses in sperm. Thus, in complex mixtures [the chemicals] co-operate to
interfere with sperm function. This has not been shown before.”
People
ingest these chemicals every day either by consuming food and drink contaminated
with them or by absorbing them through the skin in personal-care products such
as sunscreens and soaps.
Professor
Richard Sharpe, a senior scientist at the Medical Research Council Human
Reproductive Sciences Unit in Edinburgh, said: “This study appears to open up a
new dimension of potential effects of common lifestyle or environmental
chemicals on male fertility.”
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