Sperm counts among men in industrialized countries have fallen drastically over the past few decades, and the decline has left scientists puzzled.
In a large-scale review of some 7,500 previous studies conducted between 1973 and 2011, researchers spotted some startling trends. Over that time, total sperm count among men in Western countries has declined nearly 60 percent, and sperm concentration has dropped by more than 52 percent.
“Given the importance of sperm counts for male fertility and human health, this study is an urgent wake-up call for researchers and health authorities around the world to investigate the causes of the sharp ongoing drop in sperm count, with the goal of prevention,” said lead author Dr. Hagai Levine, Head of the Environmental Health Track at the Hebrew University-Hadassah Braun School of Public Health and Community Medicine at the Hebrew University of Jerusalem.
The aggregate, population-wide decline in sperm count — a key marker of man’s virility — appeared in studies from North America, Europe, Australia and New Zealand. No similar decline was found among men in Africa, Asia or South America, note the study authors.
“Decreasing sperm count has been of great concern since it was first reported twenty-five years ago. This definitive study shows, for the first time, that this decline is strong and continuing,” said Dr. Shanna H. Swan, a professor in the Department of Environmental Medicine and Public Health at the Icahn School of Medicine at Mount Sinai, New York.
Adding to the concern is that sperm-count levels haven’t taken just a single sharp drop; the multi-decade review found “no evidence of a ‘leveling off’ in recent years,” report the study authors. The findings show that the decline is steep even when considering studies going back to only 1996.
A Cause for Concern
The alarming trend has left the medical community somewhat baffled, although several theories have been floated to explain the phenomenon.
“The fact that the decline is seen in Western countries strongly suggests that chemicals in commerce are playing a causal role in this trend,” said Swan.
In particular, researchers point to phytochemicals found in numerous everyday products, such as carpets and pest sprays.
“Sperm count has been plausibly associated with multiple environmental and lifestyle influences, both prenatally and in adult life. In particular, endocrine disruption from chemical exposures or maternal smoking during critical windows of male reproductive development may play a role in prenatal life, while lifestyle changes and exposure to pesticides may play a role in adult life,” report the authors in Human Reproduction Update.
The decline is not a problem only for the chances of conception, report the study authors.
“Recent studies have shown that poor sperm count is associated with overall morbidity and mortality,” they write.
“Thus, a decline in sperm count might be considered as a ‘canary in the coal mine’ for male health across the lifespan. Our report of a continuing and robust decline should, therefore, trigger research into its causes, aiming for prevention,” conclude the study authors.