A new report reveals that sperm counts among men in Western countries, including men in North America, Australia, New Zealand and Europe, have dropped substantially over the years. According to study authors, in less than 40 years, collective sperm count among this group of men has declined more than 50%. Sperm count is currently considered the best measure of male fertility.
The new study, published Tuesday in the journal Human Reproduction Update, not only shows that men’s sperm counts are dropping, but that the continued decline does not appear to be leveling off.
“The results are indeed very profound, and even shocking,” says study author Dr. Hagai Levine, head of the environmental health track at the Hebrew University-Hadassah Braun School of Public Health and Community Medicine in Jerusalem.
While the study is not the first to suggest that men’s sperm counts are dropping, the researchers say it’s the first ever meta-analysis on the subject. The new findings have limitations—they don’t include men from non-Western countries, for one—but the researchers say the study adds to a growing body of research on how changes in environments might be affecting male fertility.
“For me it was an important scientific and public health question I had to answer: have sperm counts really declined?” says Levine. “The impact of the modern environment on health of populations and individuals is clearly huge, but remains largely unknown.”
The researchers screened 7,500 studies and found 185 that met their criteria. Studies were included in the analysis if they looked at either men who were unaware of their fertility (for example, men who had never tried to conceive) or men who were deemed fertile (for instance, men known to have conceived a pregnancy). They excluded studies with men who had been included for suspected infertility, such as men attending an IVF clinic.
They found that from 1973 to 2011, there was a steep decline of more than 50% in both sperm concentration and total sperm count among men from Western countries. The researchers also restricted the analysis to studies after 1995 and reported that the decline does not appear to be abating.
Other male fertility experts say the study helps confirm what has been suspected for some time. “This has been a recognized phenomenon for over 50 years,” says Enrique Schisterman, chief of the epidemiology branch at the National Institute of Child Health and Human Development at the the National Institutes of Health. (Schisterman was not involved in the study.) “There has never been a systematic review of the literature as this analysis has done,” he says. “I think it’s confirmatory and well done. This is a serious problem.”
The study did not explain why sperm counts might be down in this group of men, but there are several theories based on prior research performed by the study authors and other groups. Levine says that drops in sperm counts have, in the past, been associated with environment and lifestyle factors including prenatal chemical exposures, adult pesticide exposures, smoking, stress and obesity.
“One possible explanation is that men residing in Western countries over the last decades were exposed to new manmade chemicals during their life course, and there is more and more evidence that these chemicals hurt their reproductive function,” he says. “We don’t know for sure why this is happening, but our findings should drive massive scientific effort to identify the causes and modes of prevention.”
Schisterman also suspects that environmental factors may be having an impact. “I think there is a consensus in the scientific community that if the results are real, it has to be an environmental factor,” he says. “Genetics would not explain such a rapid decline.”
Levine and his co-authors argue that more research needs to be done to understand the potential causes for these widespread drops in sperm counts, as well as to find ways to prevent possible issues from arising in the first place.
“We should solve this by addressing the root causes, whether by regulation of chemicals or health promotion in the broad sense to improve diet and physical activity or tobacco control,” says Levine. “On the personal level, every man can live healthier life by reducing stress, not smoking, being physically active and keeping a good diet and weight.”