Where have all the sperm gone? In recent decades, they've been disappearing among men in Western countries; researchers have been worried about decreasing sperm counts since the early 90s. Now, the largest, most systematic review and meta-analysis of trends on the subject says sperm concentrations have declined by 52 percent and total sperm counts dropped by 59 percent among men in North America, Europe, Australia, and New Zealand between 1973 and 2011. The paper, which confirms the sperm declines first suggested in the 90s, was just published in Human Reproduction Update.
"This study provides an urgent wake-up call to investigate the causes of the sharp, ongoing drop in sperm count in order to stop further decline and even reverse it," says lead author Hagai Levine, head of the environmental health track at the Hebrew University-Hadassah Braun School of Public Health and Community Medicine in Israel. "At the moment we are dealing with the problem of male infertility down the pipe by IVF and other fertility treatments, instead of upstream [with] prevention," says Levine, who's also an adjunct assistant professor of environmental medicine and public health at the Icahn School of Medicine at Mount Sinai in New York City.
For the review, researchers from Hebrew University and Mount Sinai analyzed data from 185 studies involving 42,935 men who provided semen samples between 1973 and 2011. For the record: These men were not selected based on their fertility status; they were everyday guys. The researchers found that total sperm count (which equals sperm concentration multiplied by semen volume) declined by an average of 1.6 percent per year among men in Western countries; there was much less of a decline among men in South America, Asia, and Africa, although fewer studies have been conducted on these continents.
What's particularly worrisome: "The decline is not tapering off in Western countries—it's steep, significant, and continuing," says study co-author Shanna Swan, a professor of environmental medicine and public health at the Icahn School of Medicine at Mount Sinai.
Besides the obvious dramatic implications for men's fertility, there's the added concern that reduced sperm count is associated with a variety of health problems including an increased risk of testicular cancer, heart disease, and premature mortality. In fact, men with low sperm concentrations (below 15 million/mL) had a 50 percent greater risk of being hospitalized for any medical reason between 1977 and 2010 than those with sperm concentrations above 40 million/mL, according to a study published in the American Journal of Epidemiology this May.
While the current study didn't examine possible causes of the drop in sperm count, it does note numerous environmental and lifestyle influences that could be involved, including chemical exposures, smoking, obesity, and stress. "We have strong reasons to suspect that endocrine-disrupting chemicals and pesticide exposure play a greater role," Levine says. "Over the last decades, men and women [have been exposed] to many chemicals we were never exposed to before."
It's not just a guy's exposure to chemicals out in the world that can affect his sperm quality: What a mother does and is exposed to during pregnancy can affect the sperm concentrations of her male offspring. That's because during early pregnancy, endocrine-disrupting chemicals are affecting women in ways that could harm the reproductive development of their sons while they're in the womb, explains Swan, a reproductive epidemiologist.
Exposure in the womb can have lifelong consequences for a man's genital development and his testosterone levels. "Whatever disruption occurs in utero is permanent," Swan says. "With what a man does in life, such as smoking, the changes can be reversible," if exposure to the harmful chemical stops. But Swan notes that if a mother smokes during pregnancy, her son will end up with a lower sperm count than if he smokes as a teen or adult.
Levine told the BBC that extinction is a possibility if the trend continues, but we don't know that it will. While additional research is being done, Levine and Swan says there are steps men and women can take to protect those little swimmers. If you smoke, quit. If you're overweight, improve your diet and physical activity levels to try to lose weight, she advises. Make an effort to reduce stress. And reduce your exposure to endocrine-disrupting chemicals such as phthalates (in plastics and cosmetics), flame retardants (in furniture), and pesticides (on lawns and in fruits and vegetables), Swan says. The government and manufacturers should be addressing these risks, she adds, "but since they're not, consumers need to try to reduce their exposure whenever possible."
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