Why sperm counts in men are falling

Why sperm counts in men are falling

If scientists from Mars were to study the human male's reproductive system they would probably conclude that he is destined for rapid extinction. Compared to other mammals, humans produce relatively low numbers of viable sperm – sperm capable of making that long competitive swim to penetrate an unfertilised egg.

As many as one in five healthy young men between the ages of 18 and 25 produce abnormal sperm counts. Even the sperm they do produce is often of poor quality. In fact only between 5 and 15 per cent of their sperm is, on average, good enough to be classed as "normal" under strict World Health Organisation rules – and these are young, healthy men. By contrast, more than 90 per cent of the sperm of a domestic bull or ram, or even laboratory rat, are normal.

Human males also suffer a disproportionately high incidence of reproductive problems, from congenital defects and undescended testes to cancer and impotency. As these also affect fertility, it's a minor miracle men are able to sire any children at all. In fact, an increasing number of men are finding themselves childless. Among the one in seven couples now classed as infertile, the "male factor" has been found to be the most commonly identified cause.

Next year marks the 20th anniversary of the WHO conference where a Danish scientist first alerted the world to the fact that Western men are suffering an infertility crisis. Professor Niels Skakkebaek of the University of Copenhagen presented data indicating sperm counts had fallen by about a half over the past 50 years. Sperm counts in the 1940s were typically well above 100m sperm cells per millilitre, but Professor Skakkebaek found they have dropped to an average of about 60m per ml. Other studies found that between 15 and 20 per cent of young men now find themselves with sperm counts of less than 20m per ml, which is technically defined as abnormal. In contrast, a dairy bull has a viable sperm count in the billions.

Experts in human reproductive biology were astonished by the Danish study. The declining trend seemed to indicate that men were on a path to becoming completely infertile within a few generations (although recent studies suggest the fall in sperm counts may have bottomed out). Professor Skakkebaek could offer no explanation for the trend other than to suggest that the fall may have something to do with the equally alarming rise in other reproductive disorders, such as cancer of the testes and cryptorchidism, the incomplete descent of the testes into the scrotum.

Experts began to talk of a new phenomenon affecting the human male, a collection of disorders known as testicular dysgenesis syndrome. They wanted to know what was causing it, because the changes were occurring too quickly to be a result of genetics. It must have something to with changing lifestyles or the environment of men, and almost everything was suggested, from exposure to chemical pollutants to the modern fashion for tight underpants. There is now an emerging consensus among some experts that whatever it is that is exacerbating the problems of male infertility, it probably starts in the womb. It is not the lifestyle of men that is problem, but that of their mothers.

The process of sperm production, called spermatogenesis, starts in adolescence, but the groundwork is laid down in the few months before and immediately after birth. An increasing number of studies point to a crucial "window" of testicular development that begins in the growing foetus and ends in the first six months of life. Interfere with this critical developmental period, and a baby boy will suffer the lifetime consequences of being a suboptimally fertile man.

Read more: www.independant.co.uk

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Posted: 30/04/2010 09:05:54



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