Men living in North America, Europe, Australia and New Zealand have falling sperm counts, a newly-published study has reported.

Dr. Hagai Levine of the Hebrew University of Jerusalem led the meta-analysis of 185 studies, which involved 42,935 male participants from 50 different countries who provided semen samples between 1973 and 2011.

The analysis included other pertinent information such as age, ejaculation abstinence time, fertility status, geographic location at the level of continent and methods of semen collection and sperm count, CNN reported.

The findings, published in the journal Human Reproduction Update, revealed that the western male group had a 52.4% decline in sperm concentration and 59.3% decline in total sperm count.

Those with sperm concentrations below 40 million per milliliter are “particularly concerning,” the researchers said, as an amount below that threshold is linked to a “decreased monthly probability of conception.”

Meanwhile, there are no significant declines in the sperm concentration and sperm counts of men living in Asia, Africa and South America.

“The extent of the decline is a heartache. It’s hard to believe — it’s hard to believe for me,” Levine commented among the team composed of andrologists, epidemiologists and a qualified medical librarian.

Co-author Shanna Swan echoed the same sentiment to NBC News:

“It’s extremely worrisome. For couples who are trying to conceive, this is a very severe problem and it’s difficult psychologically, but in the big scheme of things, this is also a major public health issue.”

The analysis did not study the cause of such declines, but Levine assumed that they may be due to exposure “to many chemicals we’ve never been exposed to before.” These could be common chemicals such as lead and pesticides, which may increase or decrease the production of certain hormones that affect the reproductive system.

According to Levine, sperm count, in particular, has been previously associated with lifestyle factors such as obesity, smoking and stress.

For now, researchers appear to be in consensus that further studies must be done to trace specific causes by examining other potential variables, including associations, such as the seemingly influential role of geography. Equally, it would be interesting to explore the implications of such trends in their respective locations and the world at large.

“The impact of the modern environment on health of populations and individuals is clearly huge, but remains largely unknown,” Levine said.