The sperm count of men living in the United States and other Western countries has fallen by more than half during the past four decades, according to a major new review of the scientific literature. The study also found that the rate of decline in sperm count has not slowed in recent years.
“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,” said Dr. Hagai Levine, the study’s lead author and an epidemiologist and public health physician at the Hebrew University Center of Excellence in Agriculture and Environmental Health in Jerusalem, in a released statement.
Previous research has found that low sperm count is associated with poorer health and an increased risk — albeit, a small one — of dying prematurely.
Declining sperm counts have been reported in the scientific literature since the early 1990s, but most of those studies were considered inconclusive because they failed to take into account important confounding factors that can influence sperm count, such as age and sexual activity.
For the new study, Levine and his colleagues conducted a meta-analysis of data collected from 185 previous studies published between the years 1973 and 2011. They specifically analyzed the data on sperm concentration and sperm counts, and, important, they took into account a range of confounding factors, including age, the length of time between each man’s last ejaculation and his production of the sperm sample and the number of samples provided by each man.
The analysis of that pooled data revealed that sperm concentrations had dropped by 52.4 percent and total sperm count by 59.3 percent among men living in North America, Europe, Australia and New Zealand.
No significant decline was found among men living in South America, Asia or Africa, although far fewer studies were done in those areas of the world.
Where sperm counts have declined, the analysis also revealed no “leveling off” of the downward trend — a finding that suggests further declines in sperm counts may occur in the future.
Levine and his colleagues did not examine the reasons for the decline, but other research has suggested it may be linked to exposure both before and after birth to pesticides and other chemicals, as well as to smoking, obesity and stress.
Limitations and implications
This study used a more rigorous form of analysis than most previous research on the topic, but it still has some limitations. For example, the sperm counts of each man were assessed at a single time rather than repeatedly over many years. In addition, the meta-analysis looked only at sperm count and concentration, and not at sperm quality, which also affects fertility. It’s not clear, therefore, if the study’s findings can be used to predict fertility rates.
Also, as a research-reviewer for the Great Britain’s National Health Service noted, “Although the study did report a dramatic-sounding decline in average sperm count from 92.8 million/ml to 66.4 million/ml, this is still well within the range needed to conceive.”
Still, the findings are troubling. “Because of the significant public health implications of these results, research on the causes of this continuing decline is urgently needed,” the study’s authors write.