Sperm concentration of men in Western countries has dropped by more than 50 percent in less than 40 years and there is no evidence that the decline is leveling off, a team of international researchers warned, based on a new and comprehensive study.

“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 Dr. Hagai Levine.

Levine, head of the Environmental Health Track at the Hebrew University-Hadassah Braun School of Public Health and Community Medicine in Jerusalem, led the study along with Dr. Shanna H. Swan, professor in New York’s Icahn School’s Department of Environmental Medicine and Public Health, assisted by researchers from Brazil, Denmark, Israel, Spain and the United States.

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The findings have important public health implications. Sperm count is the best measure for male fertility, and the data shows that the proportion of the male population with sperm counts below the threshold for subfertility or infertility is increasing. In addition, recent studies have shown that reduced sperm count is also related to increased diseases and mortality among men, so the the ongoing “alarming” decline points to serious risks to male fertility and health, the researchers said.

The study also indicates that the rate of decline among Western men is not decreasing; in fact, the rate of increase was “steep and significant,” even when analysis was limited to those samples collected between 1996 and 2011. Concentration of sperm and sperm count are two parameters used to determine the quality of sperm in men.

“This is a sign, like a canary in a coal mine,” Levine said in a phone interview with The Times of Israel. “Besides the negative impact of declining sperm counts on fertility, the drop is also an alarm signal regarding the general health of humans.”

The study found a significant decline in sperm concentration and total sperm count among men from Western countries in the years between 1973 and 2011, in what the researchers say is the first systematic review and meta-analysis of trends in sperm count — a sort of a study of studies.

The paper was published Tuesday in Human Reproduction Update, a journal in the fields of reproductive biology, obstetrics and gynecology.

By screening 7,500 studies and conducting a meta-regression analysis on 185 of them between 1973 and 2011, the researchers found a 52.4% decline in sperm concentration, and a 59.3% decline in total sperm count, among men from North America, Europe, Australia and New Zealand who were not selected based on their fertility status.

In contrast, no significant decline was seen in South America, Asia and Africa, where far fewer studies have been conducted.

A problem with Western men

Even if the amount of studies conducted in non-Western countries is smaller, one can still see that the phenomenon of declining sperm is mainly a Western problem, Levine said.

The scope of the research was so wide and comprehensive that Levine decided to add teams globally to the study, which started in 2013.

Levine explained that while a major study on the subject was published already in 1992, its results, and the results of other studies that followed, have remained controversial because of certain limitations. The current research uses a broader scope and more rigorous meta-regression methods than the earlier study did, conservatively addresses the reliability of study estimates, and controls for factors that might help explain the decline, such as age, abstinence time, and selection of the study population, the researchers said.

“This definitive study shows, for the first time, that this decline is strong and continuing,” said Swan. The fact that the decline is seen in mainly in Western countries, strongly suggests that external factors like chemicals and lifestyle play “a causal role in this trend,” she said.

While the current study did not examine causes of the observed declines, sperm count has previously been plausibly associated with environmental and lifestyle influences, including prenatal chemical exposure, adult pesticide exposure, smoking, stress, and obesity.

“There is much that can be done,” to make things better, said Levine. The first is to recognize that there is a global problem and then plow more funding into research.

“Male fertility has not been researched enough and more money must be invested in research,” he said. In addition, stricter regulation, restricting or abolishing the use of harmful chemicals should be enforced.

In addition, because of cultural issues, when couples have fertility problems much of the focus is directed on women and short-term methods are used to overcome the problems, he said. “These short-term methods deal with the problem, but not the source of the problem.” And that needs to be changed.