Sperm counts have decreased by more than 50% in some wealthier nations, and that may be bad news for the future of the human race, scientists from the Hebrew University of Jerusalem and an international team of colleagues warned this week in the journal Human Reproduction Update.
The researchers, led by Hebrew University epidemiologist Dr. Hagai Levine, reviewed data from 185 different studies conducted between 1973 and 2011 and discovered that sperm counts among men in North America, Europe, Australia and New Zealand had fallen by nearly 60% in less than four decades, BBC News and New Scientist reported on Tuesday.
Specifically, the researchers conducted a meta-regression analysis of those previously-published studies and found a 52.4% decline in sperm concentration and a 59.3% drop in total sperm count among men from the affected areas, the study authors said in a statement. However, they added, no significant decline was detected among men living in Asia, Africa or South America.
While declines in sperm count have been reported since the early 1990s, the issues had remained steeped in controversy because of the limitations of previous research. However, Dr. Levine and his colleagues claim that study addresses those concerns by looking at a longer period of time, by using more rigorous analysis techniques and by controlling for possible confounding factors.
“Given the importance of sperm counts for male fertility and human health,” Dr. Levine said in an interview with New Scientist, “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.”
Causes of the observed decline remain unclear
Furthermore, the authors say that their findings indicate that the rate of sperm count decline in affected Western men is not declining, as a significant drop was detected even when they looked only at studies that used samples collected between 1996 and 2011. Should these trends continue, Dr. Levine warned, it could pose a serious threat to the future of the human race.
“If we will not change the ways that we are living and the environment and the chemicals that we are exposed to, I am very worried about what will happen in the future. Eventually, we may have a problem… with reproduction in general, and it may be the extinction of the human species,” the Hebrew University epidemiologist told BBC News.
Sheffield University professor Allan Pacey, who was not involved in the research, said that the new study “deals head-on with many of the deficiencies of previous studies” but did not remove the possibility of errors completely. “The debate has not yet been resolved,” he told BBC News, “[but] 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.”
Pacey also told New Scientist that, despite the decline, the average sperm count of Western men remained in the normal range. Possible causes of the reported decrease remain unclear, the study authors said, but previous reports have linked early exposure to chemicals used in pesticides and plastics, smoking, stress, obesity, diet and sedentary lifestyle to lower sperm counts.
Image credit: Juergen Berger