A new study shows a steady decline in French male sperm count and quality from 1989 to 2005, reflecting evidence that suggests this is a global phenomenon. The researchers call for health authorities to reinforce their action on endocrine disruptors, which have been cited as a possible environmental cause.
Reporting their findings in a paper published online first in the journal Human Reproduction on 4 December, the researchers note that as far as they know, this is the first study to find a “severe and general decrease in sperm concentration and morphology at the scale of a whole country over a substantial period”, urging that:
“This constitutes a serious public health warning.”
They suggest further studies should look for possible environmental causes.
For their research, co-author Joëlle Le Moal, an environmental health epidemiologist at the Institut de Veille Sanitaire, Saint Maurice, and colleagues, used semen analysis data from over 26,600 men attending 126 centers belonging to the French assisted reproduction technology (ART) database Fivnat.
Although the semen data came from ART centers, the men themselves were not having treatment: it was their female partners who received treatment, mostly for blocked or missing Fallopian tubes.
The researchers found that over the 17 years up to and including 2005, there has been a significant and continuous 32.2% drop in semen concentration, at a steady rate of 1.9% a year.
In men of average age 35 years, the semen concentration (or sperm count, the amount of sperm in a volume of semen) fell from an average of 73.6 million per ml in 1989 to 49.9 million per ml in 2005.
There was also a significant 33.4% drop in normally-formed sperm over the same period. The authors note that while there have been changes in the way sperm shape (morphology) is measured, they are not enough to explain all of this figure. Nevertheless, they can’t be sure this is representative of the general population.
The researchers found there was a slight increase in sperm motility (how well they move). The proportion of motile sperm went up from 49.5% in 1989 to 53.6% in 2005.
Le Moal tells the press in a statement that although the the 2005 sperm count level is still within the range the World Health Organization defines as “fertile”, it is “just an average, and there were men in the study who fell beneath the WHO values”.
And she points out:
“The 2005 values are lower than the 55 million per ml threshold, below which sperm concentration is expected to influence the time it takes to conceive.”
Although the researchers took into account as many variables that could affect the results that they could find, not all of the possible factors were available.
For instance, while they were able to adjust for age, time of year, and the center where the sperm sample was given, plus the fertilization technique, they could not adjust for socio-economic factors such as lifestyle, weight, and smoking, which can affect sperm count and quality.
But, in their discussion about this, the authors suggest even though ART is available to all in France, it tends to be people with more years of education who use it, and they are less likely to smoke and be overweight. So they argue:
“… 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 authors call for more research to look into the possible causes of this decline in male fertility.
Some studies have suggested a number of possible environmental factors, such as endocrine or hormone disruptors which can change the way genes are expressed and how cells behave.
“Impairments in the quality of human gametes (male sperm and female eggs) can be considered as critical biomarkers of effects for environmental stresses, including endocrine disrupters,” explains Le Moal.
She says gametes are the very first cells from which humans are made, and there are suggestions that early exposures (before and soon after birth, and perhaps even before conception) may have an impact on later adult health. She gives the example of the “testicular dysgenesis syndrome hypothesis”, a much debated theory currently being researched that suggests prenatal exposure to endocrine disruptors leads to abnormalities in male reproductive organs.
Another reason to be concerned, says Le Moal, is there is evidence that intergenerational effects in humans and animals can happen after the fetal stage, for instance through “epigenetic” changes that alter how genes behave:
” 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,” she says.
The authors say we should be concerned about the health of future generations.
Le Moal says they hope their “public health warning” will spur health authorities to “reinforce their actions on endocrine disruptors, hopefully at the European level, and to sustain research as well as monitoring systems”.
She says in France there are plans to implement a national monitoring system with the authority that now runs the national ART registry (the Biomedicine Agency). She hopes other countries will follow suit, and concludes:
“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 future.”
In June 2012, the Endocrine Society in the US issued a statement of principles on endocrine-disruptors and public health protection aimed at strengthening the ability of current screening programs to identify endocrine disrupting chemicals.
Written by Catharine Paddock PhD