WASHINGTON D.C. (NBC News) — A review by researchers has found that men’s sperm count around the world has been plunging for the past 40 years.

Scientists from the Hebrew University in Jerusalem and Icahn School of Medicine in New York found that there’s a 52 percent decline in sperm concentration count and a 59 percent decline in total count, after analyzing 185 studies from 1973 to 2011 including almost 43,000 men.

The meta-analysis published in the Oxford University journal, Human Reproduction Update, shows that the continued decline doesn’t appear to be leveling off, raising questions about the future of male reproductive health in western males.

“It’s extremely worrisome,” Dr. Shanna Swan, study author and professor of environmental medicine at the Icahn School of Medicine told NBC News. “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.”

No cause for the sperm count decline was given in the paper, but Swan says falling sperm counts have been linked to exposure to certain chemicals, especially for unborn boys in the womb.

“For example, a pregnant mother’s smoking has a more devastating effect on her son’s future sperm count than a man smoking as an adult,” says Swan.

The same concept may also apply to other chemicals known as “endocrine disrupters” – substances found all over the world in water, soil and some foods. It has been hypothesized that these substances can find their way into male fetuses, disrupting hormones, potentially increasing the risk for future fertility problems. Studies are under way to establish a conclusive link between these chemicals and fertility.