WEDNESDAY, Dec. 5, 2012 (HealthDay News) -- Men in France may not be quite as virile as they once were, with a new study suggesting average sperms counts have dropped over the past few decades.
According to the study, the concentration and quality of sperm in French men's semen steadily declined between 1989 and 2005. Semen concentration decreased 32 percent during this 17-year period, and there was a 33 percent drop in the percentage of normally formed sperm.
"To our knowledge, it is the first study concluding a severe and general decrease in sperm concentration and morphology [structure] 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," the French authors wrote.
The study was published online Dec. 5 in the journal Human Reproduction.
The study involved semen samples from 26,600 men who visited one of 126 assisted reproduction technology centers in France. The men's partners were undergoing treatment at the centers for blocked or missing Fallopian tubes, so the couple's infertility was not due to issues with the men's sperm.
Over the course of the study, the researchers found semen concentration among the men decreased at a rate of roughly 1.9 percent each year. Among men averaging 35 years of age, semen concentrations decreased by an average 23.7 million per milliliter to 49.9 million per milliliter between 1989 and 2005.
"The average values we have for 2005 [still] fall within the 'fertile' range for men according to the definition of the World Health Organization," study co-author Dr. Joelle Le Moal said in a news release from the European Society of Human Reproduction and Embryology.
"However, this is just an average, and there were men in the study who fell beneath the WHO values," added Le Moal, who is an environmental health epidemiologist at the Institut de Veille Sanitaire in Saint Maurice, France. "The 2005 values are lower than the 55 million/ml threshold, below which sperm concentration is expected to influence the time it takes to conceive."
Although the way sperm shape is measured changed during the course of the study, the researchers pointed out these changes do not explain the entire 33 percent decline in normally formed sperm. They added that sperm motility or movement increased slightly -- from 49.5 percent to 53.6 percent over the course of the study.
Although the researchers considered the men's age, the time of year and the fertility center the men used, they noted that they were not able to take other factors into account, such as weight and smoking, which can affect sperm concentration and quality. They pointed out that assisted reproduction technology is typically used by those with more education who are also less likely to smoke or be overweight.
"Therefore, the real values for sperm parameters in the general population could be slightly lower than those that we present and the decreases could possibly be stronger," the study's authors wrote.
The researchers said their findings support studies from other countries that revealed similar results. They concluded that more research is needed to explore the possible causes for the decrease in semen concentration and quality. Previous studies suggested that environmental factors, such as a disruption in the body's hormonal balance, may play a role in men's fertility and could affect future generations.
"Our public health warning may help health authorities to reinforce their actions on endocrine disruptors [certain environmental chemicals], hopefully at the European level, and to sustain research as well as monitoring systems," said Le Moal. "Our example could help other countries to implement their own systems. International monitoring systems could be a good idea to understand what is happening on human reproductive outcomes around the world, and evaluate public health actions in the future."
The U.S. National Institutes of Health provides more information on male infertility.