Researchers are about to deliver another blow to men's self-image by suggesting that there has been a big fall in their sperm count.
They will report today a 29% drop in the average sperm concentration in more than 7,500 men attending the Aberdeen Fertility Centre between 1989 and 2002.
Tests on nearly 16,000 samples taken in this period indicate that concentrations fell from nearly 87m sperm in a millilitre to just over 62m in the 14 years.
The figures may not be typical of the whole male population, since the men or their partners were seeking fertility treatment. But the preliminary results, reported at a joint meeting in Liverpool today of the Association of Clinical Embryologists and the British Fertility Society, will reinforce concern that either the environment or genetic changes are having a drastic effect on men's potency.
Many causes have been suggested in recent years: the toxic effects of pesticides and other chemicals, drink, smoking, obesity and tight underpants and trousers. But there is little irrefutable evidence to indicate how seriously the research should be taken.
Twenty million sperm a millilitre is regarded as the lower parameter for a "normal" sperm count. And other factors, including sperm mobility and quality, are as important in fertility. A recent Brazilian study suggested that regular coffee intake might perk up male fertility by making sperm swim faster.
Dr Siladitya Bhattacharya, who led the Aberdeen study, said: "We cannot say there has been a fall in male fertility on the basis of these preliminary results. Much conflicting evidence exists in this field.
"There has been an increase in men seeking treatment for male infertility, but whether this is due to a significant increase in this condition or because men are more aware of new techniques which have been developed to help them, we cannot say.
"Nonetheless, the drop in sperm counts must cause some concern and needs to be explained. We look forward to collecting data on other aspects of sperm quality to see if there is a similar decline."
Advisers to the Department of Health and the Food Standards Agency have urged a review of how chemicals, work and lifestyles might affect the sexual development of boys and their future fertility.
