Western Men Could Struggle to Become Fathers as Sperm Count Halves in 40 Years
Sperm quality has been a subject of much debate within the scientific community, particularly since a landmark 1992 paper that found that average sperm counts had halved in men without a history of infertility between 1940 and 1990.
Studies have implicated everything from exposure to laptops to sitting in a hot tub as possible hazards that could diminish sperm count or affect their ability to swim and, in turn, reduce men’s fertility. Others have rejected the supposed decrease in male fertility as a medical myth.
According to a new study, not only is the quality of sperm declining, but so is the quantity, at least in Western men. The study found that, between 1973 and 2011, the sperm count of men from Western countries declined by more than 50 percent—and the trend does not appear to be stopping.
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The study, published in the journal Human Reproduction Update on Tuesday, measured both sperm concentration and total sperm count. Sperm concentration refers to the number of sperm per milliliter of semen; total sperm count refers to the overall number of sperm per sample. Both are recognized measures of the quality of human sperm.
The study found that sperm concentration declined 1.4 percent per year between 1973 and 2011, resulting in an overall drop of 52.4 percent. Total sperm count went down by 1.6 percent each year, resulting in a slightly higher overall decline of 59.3 percent in the study period.
According to the study’s lead author, the results are a big concern. “For the couples who are trying to conceive, this is a very severe problem; it’s a big expense, and it’s very difficult psychologically,” says Shanna Swan, professor of environmental medicine and public health at the Icahn School of Medicine at Mount Sinai Health System in New York.
But Swan says the results have broader public health implications too. Recent studies have shown that low sperm count is associated with other health problems—including high cancer and heart disease risks, major causes of mortality in the U.S. and elsewhere—although poor sperm count has not been proved as a cause of such issues. “So men with poor sperm counts tend to die earlier,” says Swan.
The present study, by researchers at the Icahn School of Medicine and the Hebrew University of Jerusalem’s Hadassah-Braun School of Public Health and Community Medicine, was actually a meta-analysis—or study of studies—of 185 papers from 1973 to 2011, which covered 244 sperm concentration estimates derived from samples collected from almost 43,000 men.
The trends observed applied only to Western men, defined as coming from North America, Europe, Australia and New Zealand. Researchers did not observe a similar decline in non-Western men—those from Africa, Asia and South America—but admitted that this absence of a trend may be due to a lack of data. The analysis also took into account only previous studies conducted in English.
The study found a difference between men who had previously conceived a child—identified as “fertile”—and men who had never had a child and were presumed to be unaware of their fertility levels, who were referred to as “unselected.” Fertile men experienced a less significant decline in sperm concentration and sperm count than “unselected” men.
The researchers wrote that the analysis provided evidence of a “significant overall decline” in both sperm concentration and total sperm count, and that “there was no sign of ‘leveling off’ of the decline.”
The meta-analysis included only studies where sperm concentration was measured using a cell-counting device known as a hemocytometer, which the World Health Organization recommends as the best method. This approach makes the study more reliable than previous analyses of sperm quantity, says Allan Pacey, who teaches about male diseases and conditions at the University of Sheffield in the U.K.
But Pacey, who was not involved in the study, says it should be treated with caution. While the 52.4 percent decline in sperm concentration “may sound a lot,” says Pacey, the sperm were still plentiful. The decline represented a decrease from 99 million sperm per milliliter (in 1973) to 47 million sperm per milliliter (in 2011), and the latter number still falls within the “normal” range for sperm concentration.
While the researchers did not investigate the causes of a decline in sperm count, Swan says the problem starts while the male embryo is developing in its mother’s womb. Exposure to certain chemicals, maternal or paternal smoking and the mother’s stress levels and diet can all impact the embryo’s reproductive organs, which develop in the first trimester of pregnancy. However, other research has claimed that there is little evidence linking reduced sperm counts to prenatal and postnatal exposure to certain chemicals.
Swan also says further research is required to identify which chemicals contribute to falling sperm counts. And when they are identified, says Swan, regulation should be introduced to protect men from their effects. She cites the example of a chemical that was used in pesticides, dibromochloropropane, before its negative effects on male fertility were identified; the U.S. Environmental Protection Agency banned its use in 1979.
Fertility rates in the Western world are among the lowest across the globe. North American couples have an average of 1.9 children, compared with 4.7 children per couple in Africa, according to a 2015 U.N. report. If declining sperm counts reduce fertility, then that problem is likely to be compounded by women delaying pregnancy until they are in their 30s, according to Richard Sharpe, honorary professor at the MRC Centre for Reproductive Health at the University of Edinburgh. That “double whammy,” as Sharpe calls it, can have serious consequences, since alternative methods of conception can often be costly and less effective as women age.
Sharpe, who was not involved in the study, predicts that increasing numbers of couples will struggle with infertility as the trend of sperm count decline continues.
“Hopefully, this new study will serve as a wake-up call for health and research authorities, as well as for the public,” says Sharpe, “and for young people in particular.”
