A number of past international studies found the quality of the semen of young Finnish men to be among the best in the world, with the highest sperm counts in Europe. Nowadays, sperm counts have declined in one out of three men to the point of affecting fertility.
If the trend continues at the present rate, within 30 years the average Finnish male will be infertile, warns Professor Toppari.
Writing in the science periodical "Tiede", Toppari said that the situation is so alarming that the state should provide funding for continuing studies.
A long-term research project at the University of Turku, currently under way, has another two years to run.
Damage resulting in low sperm counts occurs in embryos while still in the womb. The critical causes have not been identified, but suspicions are focused on factors such chemicals in the environment and smoking by expectant mothers.
Other causes of lowered sperm quality are heavy use of cannabis, and high temperatures. Something as simple as driving a car in tight trousers can raise the temperature of the testes and reduce sperm counts.
A sharp decline in male fertility has been seen in many countries. Danish scientists published a study showing a dramatic fall in sperm counts in that country as far back as in 1992. Since then similar findings have been elsewhere, including in the USA, France and Greece.