The reproductive health of the average male is in sharp decline, the world's largest study of the quality and concentration of sperm has found.
Between 1989 and 2005, average sperm counts fell by a third in the study of 26,000 men, increasing their risk of infertility. The proportion of healthy sperm was also reduced, by a similar proportion.
The findings confirm research over the past 20 years that has shown sperm counts declining in many countries. Reasons from tight underwear to toxins in the environment have been advanced, but no definitive cause has been found.
The decline occurred progressively throughout the 17-year period, suggesting that it could be continuing.
The research was conducted in France but it has global implications. Scientists said it constituted a "serious public health warning" and the environment link "needs to be determined".
The fall in sperm counts has come along with a rise in testicular cancer – rates have doubled in the last 30 years – and in disorders such as undescended testes, which are indicative of a "worrying pattern".
There is an urgent need to establish the causes so measures can be taken, they add.
Richard Sharpe of University of Edinburgh said: "There can be little doubt that it is real, so it is a time for action. Something in our modern lifestyle, diet or environment is causing this and it is getting progressively worse."
Researchers from the Institut de Veille Sanitaire used data from 126 fertility clinics in France which had collected semen samples from the male partners of women with blocked or missing fallopian tubes.
The men, whose average age was 35, did not have fertility problems of their own and were considered representative of the general male population.
Combined with social trends such as delayed childbearing the decline in male sperm counts could signal a growing crisis for couples hoping for a family.
At age 35, female fertility is around half what it is between 20 and 25, Prof Sharpe said. (© Independent News Service)