Are male sperm counts falling generally?

Some studies do show an apparent decline in sperm count, starting with a Danish study published in 1992 that showed a 50 per cent decline between 1938 and 1990. But there are other studies that have failed to confirm this, some showing big variations in sperm counts between countries and even within countries. Since it is also known that sperm quality declines with age, making these comparisons is fraught with potential confounding factors.

The latest study shows a 29 per cent drop in sperm count between 1989 and 2002 in men attending a fertility centre in Aberdeen. This may simply because more men are coming forward for treatment.

If they are, what could be the reasons?

Many possible factors could be involved. Diet, drug use, alcohol, smoking, pollution - even, possibly, styles in underclothing - have all been suggested. But when studies show - as one did - that sperm counts in New York were twice as high as those in Los Angeles, it is difficult to think of any single factor that could account for it. A follow-up study showed that rural American males did even worse, raising the possibility that agricultural chemicals could be involved. But frankly this is all pure speculation: nobody knows the reason.

Could there be another explanation for the Aberdeen results?

The simplest explanation is that the Aberdeen team were not comparing like with like - that the men who visited the clinic in 2002 were not the same cross-section who visited in 1989. The team is now looking at sperm quality, to see if there has also been a decline there.

What can men do to prevent, or even increase sperm counts?

A healthy life style, good diet, giving up smoking and not drinking to excess might help, but nobody's promising. Wearing looser clothing, to keep the testes cooler, might also work, One French study showed that lorry drivers, who spend long hourse behind the wheel, have lower sperm counts.

Is there a link between this issue and infertility generally?

There certainly could be a link to infertility, since low sperm counts are the cause of 90 per cent of male infertility. But even men with sperm counts as low as 10 million per millilitre, far below the 62 million recorded in 2002 in Aberdeen, have more than enough sperm to become fathers - it may just take longer.

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