Scientists fear that male reproductive health is declining and say there is an urgent need to establish the causes so measures can be taken to prevent further damage. They point to the global fall in sperm counts, the rise in testicular cancer and the increase in other male sexual disorders, such as undescended testicles, as evidence of a worrying pattern that could threaten the future of the human race.
The international study of semen quality is underway in Europe (Scotland, France, Denmark and Finland) and in Japan and will be launched in the United States in the autumn. The study will assess geographical variations in the volume, concentration and motility of sperm, the level of male sex hormones and the role of chemicals in the environment.
Male reproductive health was neglected until six years ago when the Danish scientist, Niels Skakkabek, published a paper showing that global sperm counts had halved in 50 years. The paper spawned a wealth of studies but there is still no agreement on whether the fall is a global phenomenon.
Much of the controversy has surrounded differences in the way sperm counts were carried out. The new study will lay down a base line, with agreed measures, so comparisons can be made at 10-year intervals.
Stewart Irvine, of the Medical Research Council's Reproductive Biology Unit in Edinburgh and co-ordinator of the United Kingdom arm of the study, said existing evidence suggested that sperm counts were falling twice as fast in Europe as in the US - at 3 per cent a year compared with 1.5 per cent. British men have sperm counts almost twice as high as the Danish (90 million per millilitre compared with 50 million) but only three-quarters that of the Finnish (120 million).
However, sperm counts will have to fall a long way before they cause problems with fertility because of the large safety buffer that nature has provided: only one sperm is needed to fertilise an egg.
A bigger worry is the rise in testicular cancer which mainly affects young men. In the UK, the rate doubled between 1962 and 1986 and now stands at around 10 cases per 100,000 men, twice the rate in Finland (5 per 100,000) but less than half that in Denmark (25 per 100,000).
Although Finland has a lower testicular cancer rate and a higher sperm count than Denmark or the UK, the rate of increase in testicular cancer in Finland is higher. "Whatever is going on is going on at different rates in different countries. If it is an environmental factor, the Danes may have been exposed to it longer," Dr Irvine said.
Environmental pollution is the most likely cause of the decline in male reproductive health. Most experts blame industrial chemicals, including the pesticide DDT and those used in making plastics, which mimic the hormone oestrogen in their effect on the body, bringing out feminine characteristics or counteracting male hormones.
Dr Irvine said: "The use of agro-chemicals in Denmark is enormous. Whether that is relevant we don't know but it is a suspect."
An alternative theory blames changes in lifestyle. People are waiting longer to have children and fertility declines with age.
Harry Fisch, director of the male reproductive centre at the Columbia Presbyterian Medical Centre in New York, said in the Lancet journal: "Many of the men [seeking treatment for infertility] are overweight, they don't exercise, they smoke and they take all kinds of herbs and hormone-containing supplements. You see all these risk factors yet men blame some environmental factor when they should blame themselves."
However, he added: "There is no smoke without fire. The changes we have seen indicate we are facing a worrying public health question. It is important we address it before something serious does come along."Reuse content