Sperm counts of Western men are in a “shocking” downward spiral that poses a potential threat to fertility in industrialised countries, a major study has found.
Scientists documented a 59.3% drop in the average amount of sperm produced by men from North America, Europe, Australia and New Zealand between 1973 and 2011.
The trend appeared to be ongoing since the rate of decline remained “steep and significant” in the last 15 years of the analysis.
One possible cause could be environmental chemicals, it is claimed.
Dr Hagai Levine, from the Hebrew University of Jerusalem, who co-led the research, said it is “an urgent wake-up call for researchers and health authorities around the world to investigate the causes”.
Professor Daniel Brison, scientific director of the Department of Reproductive Medicine at the University of Manchester, described the findings as “shocking”, adding that this is “the most comprehensive to date” bid to study the problem.
The research was published in the journal Human Reproduction Update, and is based on a rigorous analysis of pooled data from 185 carefully-screened studies.
Co-author Professor Shanna Swan, from the Icahn School of Medicine at Mount Sinai, New York, said: “Decreasing sperm count has been of great concern since it was first reported 25 years ago.
“This definitive study shows, for the first time, that this decline is strong and continuing.
“The fact that the decline is seen in Western countries strongly suggests that chemicals in commerce are playing a causal role in this trend.”
Environmental and lifestyle factors including exposure to chemicals in the womb, adult exposure to pesticides, smoking, stress and obesity have all been previously linked to falling sperm counts.
Many experts believe falling sperm count may act as a “canary in the coal mine” signalling broader risks to health.
Professor Richard Sharpe, from the Medical Research Council Centre for Reproductive Health at the University of Edinburgh, pointed out that in northern Europe today more than 15% of young men have a sperm count low enough to impair fertility.
He added: “As the present study indicates, this is likely to get worse rather than better as we move forwards in time. What is not so widely appreciated is that the coincidence of this change in men with delay in couples trying for a baby until the female partner is in her 30’s (when her fertility is declining progressively), creates a double whammy for couple fertility in modern Western societies.
“Whilst assisted reproduction techniques (ART) can potentially remedy this for some, ART is costly, highly invasive for the female partner and also becomes progressively less effective with female age. Therefore, looking ahead, I can only conclude that couple infertility is set to increase.”
Allan Pacey, professor of andrology at the University of Sheffield, said he had not been convinced by previous studies claiming to have found evidence of falling sperm counts, which were flawed by various kinds of bias.
However the new research had dealt “head on” with many of these issues.
He stressed that despite the decline reported in the study, average sperm counts remained in the “normal” range.
Prof Pacey added: “The debate has not yet been resolved and there is clearly much work still to be done. However, the paper does represent a step forward in the clarity of the data which might ultimately allow us to define better studies to examine this issue.
“Ideally, we would have funded large prospective epidemiological studies of healthy males 25 years ago and this would by now have given us a clear answer one way or the other.”