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Sperm count is in steep decline. A large review has found a 40-year plunge in sperm count, specifically in men from North America, Europe, Australia and New Zealand — and the reason may be associated with common factors in our daily lives.

Scientists from the Hebrew University in Jerusalem and Icahn School of Medicine in New York analyzed 185 studies from 1973 to 2011, including almost 43,000 men. The results were stunning: Researchers found a 52 percent decline in sperm concentration and a 59 percent decline in total sperm count.

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.”

The new paper doesn’t give reasons for the decline.

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Related: You Won't Believe What Baby-Making Science Could Soon Deliver

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.

But sperm count has broader health implications than just fertility.

“Male fertility predicts overall men’s health”, says Dr. Joseph Alukal, urologist and director of male reproductive health at NYU Langone Health. Studies have shown that lower sperm counts may predict shorter life expectancy and are associated with heart attacks.

What about Tighty Whities?

Cause-and-effect is unclear at this point, said Alukal. But there are culprits of modern life that both lower sperm count and increase the risk for other common health conditions: a sedentary lifestyle, often accompanied by a poor diet.

Related: America's Obesity Epidemic Hits a New High

Alukal recommends four simple things men can do to not only achieve better overall health, but also increase the count of their little swimmers:

a healthy diet

exercise

no smoking

better sleep

“Plus they’re easy to do and they cost no money”, says Alukal.