Experts have disputed whether the sperm counts of men are shrinking globally for decades. Now, new findings published in the journal Human Reproduction Update reveal that sperm counts dropped throughout the Western world by more than half during a period of nearly 40 years, reports CNN.

For the study, an international team of scientists from Brazil, Denmark, Israel, Spain and the United States reviewed thousands of studies. Next, researchers examined data from 185 studies that included 42,935 male participants from 50 different countries who provided semen samples between 1973 and 2011. Information included men’s fertility status, age and ejaculation abstinence time, as well as semen collection method, sperm count method and geographic locations at the level of continent.

Results showed that there was a reduction in sperm concentration of 1.4 percent per year with an overall drop of 52.4 percent for men living in North America, Europe, Australia and New Zealand for the length of the study. In addition, researchers also noted a decline of 1.6 percent per year in total sperm count among the same group that totaled 59.3 percent overall. Interestingly, the research team failed to find any significant declines in sperm count and sperm concentrations of men who lived in South America, Asia and Africa.

Scientists said that sperm concentrations below 40 million merit concern because they are associated with “decreased monthly probability of conception.”

While the assessment didn’t delve into the cause of declines in sperm count, researchers suggested that this reduction might be the result of exposure to endocrine-disrupting chemicals, obesity and global warming.

“The impact of the modern environment on health of populations and individuals is clearly huge but remains largely unknown,” said Hagai Levine, an epidemiologist from the Hebrew University of Jerusalem and the study’s lead author. “Sperm count has previously been plausibly associated with environmental and lifestyle influences, including prenatal chemical exposure, adult pesticide exposure, smoking, stress and obesity. Every man can reduce exposure to chemicals, avoid smoking, keep balanced diet and weight and reduce stress.”

Scientists concluded by calling for more research to be conducted on the subject.

Click here to read how fast food can disrupt hormonal health.