The concentration of sperm among men in North America, Europe, Australia and New Zealand has dropped by more than half in less than four decades, according to the first systematic review and meta-analysis of trends in male fertility.
“These are dramatic and shocking results that involve not only reduced male fertility but also reflect danger to the health of males,” chief researcher Dr. Hagai Levine, head of the environmental health track at the Hebrew University of Jerusalem-Hadassah Braun School of Public Health and Community Medicine, told The Jerusalem Post on Tuesday.
“Decreasing sperm count has been of great concern since it was first reported 25 years ago.
This definitive study shows for the first time that this decline is strong and continuing. The fact that the decline is seen in Western countries strongly suggests that chemicals in the environment are playing a causal role in this trend,” added Swan.
Levine spent 2014 at the Icahn School of Medicine researching the subject – along with environmental medicine and public health Prof. Shanna Swan – at Mount Sinai Hospital in New York City, and an international team of researchers from Brazil, Denmark, Israel, Spain and the US.
The study, just published in Human Reproduction Update
– the leading journal in the fields of reproductive biology, obstetrics and gynecology – has aroused great concern among physicians and scientists as well as in the general media.
Low sperm counts are worrisome not just because of fertility issues but because they are associated with cryptorchidism (the absence of one or both testes from the scrotum), hypospadias (a congenital condition in which the opening of the urethra is on the underside of the penis) and testicular cancer, suggesting a shared prenatal cause.
The rigorous and comprehensive meta-analysis of data collected between 1973 and 2011 found that – among men from Western countries who were not selected on the basis of their fertility status – sperm concentration declined by more than 50%, with no evidence of a leveling off in recent years.
These findings, Levine said, strongly suggest not only a significant decline in male reproductive health, but also the general health of men, given the evidence linking poor semen quality with higher risk of hospitalization and death. Research on causes of this ongoing decline and their prevention is urgently needed, the team urged.
By screening 7,500 studies and conducting a meta-regression analysis on 185 studies, the researchers found a 52.4% decline in sperm concentration and a 59.3% drop in total sperm count among men from North America, Europe, Australia and New Zealand who were not selected based on their fertility status. British studies have also found a lower sperm count in dogs, but the cause is not known.
By contrast, no significant decline was seen in men from South America, Asia and Africa.
However, in these continents, far fewer studies have been conducted. Studies of sperm counts and a lower quality of donations to sperm banks have also shown declines in Israel in recent years.
The study also indicated the rate of decline among Western men is not decreasing – the slope was steep and significant even when analysis was restricted to studies with sample collection between 1996 and 2011.
While drops in sperm counts have been sporadically reported since 1992, the question has remained controversial due to limitations in past studies that raised considerable doubt about the findings. The current study uses a much broader scope and rigorous meta-regression methods, conservatively addresses the reliability of study estimates, and controls for factors that might help explain the decline, such as age, abstinence time and selection of the study population, Levine said.
“Given the importance of sperm counts for male fertility and human health, this study is an urgent wake-up call for researchers and health authorities around the world to investigate the causes of the sharp ongoing drop in sperm count, with the goal of prevention,” maintained Levine.
“I deal with the main problems of public health, and this phenomenon in male fertility is very significant. Smoking is major problem, even more in the pregnant mother than of the father, as they change the production of hormones in the male fetus that affect the development of the testes.”
While the current study did not examine causes of the observed declines, sperm count has previously been plausibly associated with environmental and lifestyle influences, including smoking, prenatal chemical exposure, adult pesticide exposure, stress, using laptops while on the lap, obesity and even regular bicycle riding. Therefore, sperm count may sensitively reflect the impact of the modern environment on male health across the lifespan and serve as a “canary in the coal mine” signaling broader risks to male health, Levine said.
Thus, he added, sperm counts are a barometer of the effects of the environment on humans. “We can’t say exact what causes low counts, as more research is needed, but people are now exposed to a huge amount of things that man was never exposed to before,” Levine said.