Has Worldwide sperm counts declined?

It was back in 1992 that a Danish study first suggested that worldwide sperm counts had declined - by an extraordinary 50 per cent from 1938 to 1991. Various chemicals, alcohol, smoking and diet were all blamed. However, there was no evidence of an actual infertility crisis worldwide. Indeed, the global population continued to rise and last year passed the seven billion milestone. Scientists also queued up to point out the flaws in the Danish study, citing a lack of standardisation in the collection and analysis of semen and how the results were interpreted.

Last year, a more rigorous Danish study looking at 15 years of data collected from young men entering military service, showed no decline in sperm counts at all. If there is a worldwide problem, one would expect Denmark to be part of it. An unusual number of Danes smoke, for example, and, as an industrialised nation, it is awash with the sort of chemicals that campaigners claim damage male fertility.

That said, there is no doubt that more and more couples, especially in the West, are finding it difficult to conceive. Although sperm counts may not be in huge decline, sperm quality may be deteriorating. A 1996 study in France found a significant decline in sperm quality over a 20-year period.

In general, a major factor is age - many people, men as well as women, are leaving it until well after their fertility has peaked to try for their first child. A combination of factors including stress, too much alcohol, rising levels of obesity, too little sleep and, probably, some synthetic chemicals can cumulatively affect the quality and quantity of sperm.

Male fertility is complicated. The partners of men with low sperm counts (or very low-quality sperm) can get pregnant, and it is only when men produce zero or almost no sperm that they can be considered truly infertile.

So the advice is: don’t smoke, eat well, drink in moderation and get plenty of exercise. And don’t leave it too long.