An analysis of hundreds of studies covering data from over 50 countries across six continents has shown an alarming downward trend in sperm counts, and researchers are warning that the decline could have far-reaching implications not just for fertility, but also for overall health and mortality.
The analysis was published in the Human Reproduction Update and included data collected from just under 43,000 men between 1973 and 2011. In that 40-year span, researchers found that sperm counts more than halved in Western countries like Canada, the U.S., the U.K., and Australia — where sperm declines were the sharpest.
Globally, the authors of the study estimated that average sperm concentration has fallen to 66.4 million per mL from around 92.8 million per mL, meaning that average sperm concentration is declining by around 0.75 per cent each year.
But when researchers selected just Western men who hadn’t had children yet, they found an even more pronounced drop. In 1973, people in this group had an average sperm concentration of 99.0 million per mL, which is higher than the global average at that time. But by 2011, that concentration plummets to 47.1 million per mL, a decline of 1.4 per cent each year.
Western men in this demographic also saw the sharpest drop in total sperm count, which researchers found declined by 59.3 per cent since the 1970s.
Fertile Western men, or people who had known children at the time their sperm samples were taken, saw a similar decline in sperm concentration from an average of 83.8 million per mL in 1977 down to 62.0 million per mL by 2009.
Declines in sperm counts were less pronounced in non-Western countries, but researchers said this could be due to a lack of historical data.
Researchers did find that the trend of declining sperm counts has been accelerating over time. When the authors of the study looked at data collected globally since 1972 vs. data collected only since 2000, they found that recent sperm concentrations were declining about two times faster than they once were.
The findings of this study have lead author Hagai Levine from Hebrew University of Jerusalem raising the alarm about a potential reproductive crisis.
Studies have suggested that fertility is compromised when sperm concentrations are lower than 40 million per mL. While this is still lower than the average sperm concentration for Western men, it’s pretty close, meaning there’s a significant portion of men who fall below that threshold.
“Such a decline clearly represents a decline in the capacity of the population to reproduce,” Levine said.
But declines in sperm count don’t only affect fertility, the experts warn.
“A decline in sperm count might be considered as a ‘canary in the coal mine’ for male health across the lifespan,” according to the study.
Researchers wrote that there have been numerous other worrying trends in male reproductive health, relating to testicular germ cell tumours, cryptorchidism (when testicles fail to descend into the scrotum), onset of male puberty and total testosterone levels. They also pointed to other studies that have shown an association with poor sperm count and overall mortality.
The study has no definitive answer for what is causing this decline in sperm counts, but hypothesized that exposure to endocrine-disrupting chemicals or maternal smoking during pre-natal development could be contributing to the problem.
Researchers also said that certain lifestyle choices like smoking, drinking, and a poor diet, as well as exposure to pesticides during adult life, can also impact sperm counts.