Are men's sperm counts in a slump — for the last 40 or so years?
A new study finds that men in North America, Australia and Europe produced less than half as many sperm in 2011 compared with 1973. Equally alarming: The quality was worse.
The research raises concerns about fertility as well as male health. Studies show that men with lower sperm counts are more vulnerable to certain cancers, heart disease, diabetes and early death.
“I was really scared when I saw this paper,” said Tina Kold Jensen, an epidemiologist and professor at the University of Southern Denmark, who did not participate in the study.
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Jensen said she was involved in research 20 years ago that came to the same conclusion but assumed that sperm counts would have stabilized or bounced back since. “I was actually surprised by the findings. I didn’t think it would go on like that.”
The research, published Tuesday in the journal Human Reproduction Update, compiled data from 185 different studies that included nearly 43,000 men in North America, Europe, Australia and New Zealand. In some cases the men had their semen counted because they were suffering from infertility or other medical problems, which could skew the study’s results.
But the trend looked even stronger among men who didn’t have a medical reason to get their semen checked, said Shanna Swan, the paper’s senior author and a reproductive endocrinologist and professor at the Icahn School of Medicine at Mount Sinai in New York.
Swan said she began researching semen counts and quality more than 20 years ago after seeing the declines reported in earlier research — and not believing them. “I’ve done my best to make those declines go away,” she said, describing the statistical analyses she conducted to try to undercut that research. When she couldn’t, she became convinced that the decline was real.
Sperm counts fell an average of 1.6% a year for an overall decline of 59.3% since 1973, according to the new study. Sperm concentration, a measure of quality, also declined dramatically over the same period, particularly among fertile men. The trend did not improve or worsen in more recent decades.
The idea of falling sperm counts has been controversial since it was first suggested 25 years ago. Delores Lamb, director of the Center for Reproductive Medicine at Baylor College of Medicine in Houston, still doesn’t buy it. Counting semen can be tricky and is often unreliable, she said. Many factors might affect why a man’s count could be off one day, including stress and time of year.
While she believes studying semen count is crucial, she says much more research is needed to confirm any trend.
Michael Eisenberg, a urologist and assistant professor at Stanford University, agrees that the data have some flaws but says it’s enough to justify further investigation. “As a species, we should be concerned if there’s a trend toward declining fertility,” he said. “There’s an urgent need to track this a little more rigorously.”
If sperm counts are truly falling, what could be the cause? No one is really sure, but there are a lot of suspects.
Smoking, particularly by women pregnant with boys, might affect their sons’ fertility decades later, Swan and others said. But it’s not the full story. Kold Jensen said that while smoking rates have fallen in Denmark in recent decades, she’s seen no improvement in sperm count.
Growing rates of obesity and sedentary lifestyles may share some of the blame for any drop in sperm count, as could pesticide use, several researchers said. While eating more fruits and vegetables promotes health, the chemicals sprayed on them can reduce sperm count, said Hagai Levine, an epidemiologist and public health physician at Hebrew University-Hadassah Braun School of Public Health in Jerusalem who was the lead author in the new study.
Stressful life events, such as a move, job change or divorce, can reduce sperm count, too, Swan said.
Some experts also worry that so-called endocrine-disrupting chemicals — which can be found in everything from canned food to cosmetics — could be major contributors to falling sperm counts.
To protect against a low sperm count, there are a few things men can do.
In some cases, exercise and losing weight can improve the count and boost fertility, Kold Jensen said.
It’s also possible to reduce chemical exposures by eating fewer canned foods and more organic fruits and vegetables, not microwaving in plastic and regularly opening windows at home to allow chemicals to escape, said Leonardo Trasande, a pediatrician at the New York University School of Medicine who studies the impact of the environment on health.
Pregnant women should also take care to avoid pesticides and other chemicals, he said. Unfortunately, though, by the time a woman knows she’s pregnant, it may already be too late. The male reproductive organs are formed near the end of the first trimester, Kold Jensen said.