Sperm count—an indicator of male fertility as well as overall health—has dropped more than 50 percent over the last 40 years among men in North America, Europe, Australia, and New Zealand, according to a recent paper that researchers say highlights a concerning public health trend.
For the study, researchers from Hebrew University of Jerusalem and Icahn School of Medicine in New York assessed more than 7,500 peer-reviewed papers. The final review—which included 185 papers that involved nearly 43,000 men worldwide—was published in the journal Human Reproduction Update.
According to Newsweek, the latest study was designed to address concerns about previous studies on male infertility. Earlier research into sperm counts has drawn criticism over the reliability of the underlying data, Newsweek reports, with some scientists contending older sperm-counting methods may have inflated sperm counts, making the decline look much sharper than it is. In fact, according to Quartz, "there has been a longstanding debate among scientists as to whether sperm counts have decreased."
To address those concerns and others, the latest review did not include any research conducted prior to 1973, so as to exclude studies reliant on imprecise measures of sperm count, and rejected any studies involving men who had recorded fertility issues or who smoked tobacco.
The researchers found that sperm levels among men in North America, Europe, Australia, and New Zealand fell from an average concentration of 99 million in 1973 to 47.1 million in 2011—a 52 percent decline.
The researchers also found that the sperm count among men from these continents declined by an average of 1.4 percent annually, with researchers reporting an average overall sperm count decline of 52.4 percent over the time period studied.
As the data stand now, even with the recorded declines in sperm count, the average sperm count "still leaves most men on the normal side of fertile," Newsweek reports. However, according to Quartz, "if the data on sperm counts is extrapolated to its logical conclusion, men will have little or no reproductive capacity from 2060 onwards." Sperm concentration below 40 million can impair fertility, according to the researchers.
The researchers did not observe a decline in sperm counts in men from Asia, Africa, or South America. However, the researchers noted that data from those areas were limited. And, according to Newsweek, prior research has found large declines in countries such as China and Japan.
What's driving the decline?
The researchers did not identify what was causing the decline in sperm levels.
However, according to Newsweek, other research suggests some possible factors could be increasing rates of obesity, lower levels of activity, and toxins in the environment—namely, endocrine-disrupting chemicals found in compounds such as BPA and phthalates. Such chemicals, which can interfere with testosterone, are present in plastics.
Researchers sound the alarm
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Most experts say the data in the new study are of high quality and that its conclusions are alarming, Quartz reports. For instance, while calling for further research into what's causing the declining sperm count, Michael Eisenberg, a urologist and an associate professor at Stanford University, said, "There have been some good counterarguments about sperm-level decline, but this paper really puts a lot of those arguments to bed."
And researchers expressed concern about what the findings could mean for men's health more broadly. Shanna Swan, an author of the study and professor of environmental medicine at the Icahn School of Medicine, called the findings "extremely worrisome" and "pretty scary." According to Swan, the overall decline in male sperm levels "in the big scheme of things ... is ... a major public health issue."
Hagai Levine, another author of the study and a public health research at the Hebrew University, similarly expressed concern. "Reproduction may be the most important function of any species," he said. "Something is very wrong with men."
In fact, as Germaine Louis, the director and senior investigator at the Eunice Kennedy Shriver National Institute of Child Health and Human Development, points out, semen level counts are, "like blood pressure," a good measure of overall male health. "Semen quality isn't just about a couple getting pregnant," he said. "There is increasing evidence at the population level that men with diminished semen quality die earlier and have more chronic diseases. This is as important to health as any disease state" (Barratt, Quartz, 7/28; Walsh, Newsweek, 9/12; Gussone, NBC News, 7/25; Levine et al., Human Reproduction Update, 7/25).
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