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（形态学） at the scale of a whole country over a substantial period.

 

"This constitutes a serious public health warning."

 

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 infertility², 15 million per millilitre."

 

There has much been much debate in the past 20 years over whether sperm quality has decreased, with research supporting both sides of the controversy³. This latest research adds weight to the numerous European studies that suggest one in five young men has a sperm count low enough to impair⁴ 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（祸不单行） 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 aged⁵ between 18-70 whose partner's were undergoing fertility treatment because of blocked or missing fallopian tubes（输卵管）.

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