The average sperm count of men may have fallen by as much as 29 per cent over the past 12 years, according to a large new UK study.

Sperm concentration among men attending the Aberdeen Fertility Centre in Scotland fell from 87 million per millilitre to 62 million per millilitre between 1989 and 2002. Nearly 16,000 samples were taken from 7500 men.

The dramatic decrease surprised doctors at the clinic, although concentrations above 20 million per millilitre are considered to be healthy.

Aberdeen University’s Siladitya Bhattacharya, who led the study, acknowledges that the results might be skewed by the fact that the subjects were attending a fertility clinic. “That is an inescapable fact. We weren’t able to get a truly random sample,” he says. “Nevertheless, the drop in sperm counts must cause some concern, and needs to be explained”

The results, presented on Monday at the Joint Meeting of the Association of Clinical Embryologists and British Fertility Society, may also not be typical of the whole of the UK.

Tight trousers

But there is growing evidence that environmental factors can cause sperm counts to fall. Drug use, smoking, excessive drinking, obesity, and even tight fitting trousers have all been blamed.

Environmental toxins such as pesticides has also been proposed as causes of declining sperm counts, while a study published in July 2003 showed that chemicals mimicking the action of estrogen and found in some foods can impair the normal functioning of sperm.

However, despite the large number of studies in many parts of the developed world, no consensus has been reached on why men sperm counts are dropping.

Alan Pacey, of the British Fertility Society, told the BBC that the study would help researchers piece together the “jigsaw” of evidence. “British men actually fare quite badly on the European stakes and the region of Europe which is known to have the highest sperm count is Finland,” he said.

The Aberdeen researchers plan to compare other aspects of the sperm samples, such as motility, to see if their overall quality has declined in the same way as their concentration.

More here.