Semen Concentration and Quality Fell in French Men Between 1989 and 2005

http://www.sciencedaily.com/releases/2012/12/121205083836.htm

ScienceDaily (Dec. 3, 2012) — New research shows that the concentration of sperm in men's semen has been in steady decline between 1989 and 2005 in France. In addition, there has been a decrease in the number of normally formed sperm.

The study is published online today in Europe's leading reproductive medicine journal Human Reproduction.

The study is important because, with over 26,600 men involved, it is probably the largest studied sample in the world and although the results cannot be extrapolated to other countries, it does support other studies from elsewhere that show similar drops in semen concentration and quality in recent years.

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They found that over the 17-year period there was a significant and continuous 32.2% decrease in semen concentration (millions of spermatozoa per millilitre of semen), at a rate of about 1.9% per year. The researchers calculated that in men of the average age of 35, semen concentrations declined from an average of 73.6 million/ml in 1989 to 49.9 million/ml in 2005.

In addition, there was a significant 33.4% decrease in the percentage of normally formed sperm over the same period. Changes in the way sperm shape (morphology) was measured during this time may partly explain this decrease and make it difficult to give an estimate for the general population. However, the researchers say that these changes do not account for the total decrease in the quality of sperm morphology observed over the study period.

In their paper, the researchers write: "To our knowledge, it 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. The link with the environment particularly needs to be determined."

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The authors say that there needs to be more research into the possible causes for the decline in semen concentration and percentages of normally formed sperm, but other studies have pointed to the role played by environmental factors such as endocrine disruptors (chemicals that disturb the body's normal hormonal balance). Furthermore, such factors could induce epigenetic changes (changes in the way genes and cells behave) that might be passed down the generations, and which could contribute to a longer process of decline in men's fertility.

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"Secondly, it has been shown in humans and animals that intergenerational effects may occur after foetal exposures, particularly via epigenetic changes. If such exposures and effects occur in successive generations, accumulated outcomes are plausible. So the observed trends could be the result of several generations' changes."

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