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By Anna-Marie Lever Health reporter, BBC News
The sperm count of French men fell by a third between 1989 and 2005, a study
suggests.
The semen of more than 26,600 French men was tested in the study, reported in
the journal Human Reproduction.
The number of millions of spermatozoa per millilitre fell by 32.3%, a rate of
about 1.9% a year. And the percentage of normally shaped sperm fell by 33.4%.
The average sperm count remained within the fertile range, but experts want to
see more research into possible causes.
One of the paper's authors, Dr Joelle Le Moal, an environmental health
epidemiologist, said: "To our knowledge, this is the first study concluding a
severe and general decrease in sperm concentration and morphology at the scale
of a whole country over a substantial period.
"This constitutes a serious public health warning."
Start Quote
Something in our modern lifestyle, diet or environment like chemical exposure,
is causing this.
Prof Richard Sharpe University of Edinburgh
But Dr Allan Pacey, senior lecturer in andrology at the University of
Sheffield, said: "The change in sperm concentration described, 73.6 to 49.9
million per millilitre [on average for a 35-year-old], is still well within the
normal range and above the lower threshold of concern used by doctors which is
suggestive of male infertility, 15 million per millilitre."
There has much been debate in the past 20 years over whether sperm quality has
decreased, with research supporting both sides of the controversy. This latest
research adds weight to the numerous European studies that suggest one in five
young men has a sperm count low enough to impair fertility.
Prof Richard Sharpe, from the University of Edinburgh, said: "Something in our
modern lifestyle, diet or environment like chemical exposure, is causing this.
"We still do not know which are the most important factors, but perhaps the
most likely is a combination, a double whammy of changes, such as a high-fat
diet combined with increased environmental chemical exposures."
The study analysed data from the French database Fivnat, which logs information
from 126 assisted reproduction centres. Researchers examined semen samples
provided by men aged between 18-70 whose partners were undergoing fertility
treatment because of blocked or missing fallopian tubes.
'Jury out'
As the study took place over a period of years, it is important that methods
remained the same for comparison- but critics have questioned this.
Dr Pacey said: "In the paper, the authors claim that the methods for
measurement of sperm concentration and motility 'have not changed noticeably
during the study period', yet to me this is an odd thing to say as in my
experience they have changed remarkably everywhere else in the world.
"I would argue that the 'jury is still out' on this issue."
While the study took into account factors that can affect sperm quality, such
as age, researchers were unable to control for socio-economic factors, smoking
or weight, which have been shown to have a major impact.