Plummeting Sperm Counts Cause Concern
Halweil, Brian, The Futurist
Developed countries may see widespread infertility, falling birthrates.
The average sperm count - the number of individual sperm in a given volume of semen - of men in the United States and Europe has plummeted by over 50% since the late 1930s, according to a recent analysis. The finding fuels ongoing concerns that male reproductive health may be deteriorating and that environmental pollutants may be the cause.
Results of 61 studies involving nearly 15,000 subjects show that average sperm counts among healthy American men dropped from 120 million sperm per milliliter of semen in 1938 to just under 50 million in 1998, a decline of 1.5% a year. In Europe, sperm counts fell by roughly the same amount between 1971 and 1990, though twice as fast - by 3.1% each year.
Only one sperm is required to fertilize an egg, but once a man's sperm count drops below 20 million per milliliter, infertility becomes increasingly common.
There appears to be considerable geographic variation in sperm counts. While declines have been demonstrated in Danish men, for instance, Finnish sperm counts appear unchanged. Studies in four U.S. cities show considerable variation in average sperm count. And a recent study suggests that sperm counts may vary considerably even within the city of London.
Considerable controversy revolves around the proposed causes of declining sperm counts, though the prevailing explanation - the "endocrine disruption" hypothesis - implicates environmental chemicals that masquerade as hormones. Since hormones such as estrogen or androgen orchestrate the development and everyday function of organisms, exposure to hormone-mimicking chemicals can disrupt these development signals.
Researchers are specifically looking at "environmental estrogens" - synthetic chemicals that mimic the female sex hormone estrogen. These chemicals may influence boys' development when they are very young or even when their mothers are still carrying them. It is in these very early stages of development that hormone sensitivity is high and proper function of the male reproductive tract can be easily derailed.
Abundant clinical evidence supports this hypothesis. Lab animals exposed to even traces of estrogen-mimicking chemicals have been found to develop reproductive disorders ranging from testicular cancer to infertility. …