Scientists carried out the first nationwide study of semen quality on young Swiss men and found only 38 per cent of them had above average quality sperm.
Seventeen per cent are considered "subfertile" and likely to struggle to have children, according to thresholds set by the World Health Organisation (WHO). This means they have sperm concentrations of less than 15 million per ml of semen.
The median concentration of sperm ranges between 41 to 67 million per ml of semen for young European men. Swiss men have an average of 47 million per ml, according to the study, published in the journal Andrology.
“It’s important to understand that the time needed to conceive increase significantly if a man has a sperm concentration below 40 million sperm per ml,” said Professor Serge Nef from the University of Geneva (UNIGE), who helped carry out the research.
Men from Lithuania, Estonia and Spain are believed to have the highest quality sperm, although direct comparisons are difficult because research is done differently in each country. There is currently no comparable data on the UK.
Generally there has been a marked decrease in sperm count across industrialised countries but scientists do not currently know why.
Professor Nef told The Independent it could be caused by environmental factors such as pesticides or lifestyle factors such as smoking, drinking alcohol, taking drugs or being overweight.
“That’s what several laboratories throughout Europe are currently investigating,” he said.
Current research suggests it is more common among men who were exposed to maternal smoking during embryonic development.
Researchers tested the semen quality of 2,500 men between the age of 18 and 22 as part of their military recruitment. The men came from every area of Switzerland and were conceived and born in the country.
Participants completed the questionnaire about their health, lifestyle, diet and education. Their parents also filled in a similar questionnaire.
Scientists assess semen quality by looking at sperm concentration (the number of sperm per ml), their ability to get around and their shape.
“Low semen parameters values can reflect a men’s fertility, when a combination of values are low, a men’s ability to conceive is at risk,” said lead researcher Rita Rahban who is a PhD student at UNIGE.
Dr Alfred Senn, an andrologist and co-author of the study said that a single semen analysis is not “entirely predictive” or a person’s fertility.
However he warned that “the sperm quality of young men in Switzerland is in a critical state and that their future fertility will in all likelihood be affected.”
The study did not identify differences in sperm quality between Switzerland’s various geographical regions or linguistic areas. There was also no differences between urban or rural regions.
Poor semen quality is also associated with an increase in the incidence of testicular cancer and genital malformations.
”For 35 years, testicular cancer has grown steadily to over 10 cases per 100,000 men, which is very high compared to other European countries. Sperm quality is generally lower in countries where the incidence of testicular cancer is high,” said Professor Nef.
This is almost certainly the result of altered testicular development at the foetal stage, scientists say.
The number of infertile couples in Switzerland using assisted reproductive technology (ART) doubled from 3,000 to over 6,000 a year between 2002 and 2010.
The only UK data on the subject comes from men who have been to infertility clinics so could not be compared to the Swiss study.
However, the NHS says problems with sperm are quite common. In the UK, they are a factor in around one in three couples who are struggling to get pregnant.