In the largest study of its kind, researchers find that sperm count in Western countries has more than halved in recent decades. Outside of these countries, however, the decline is not significant.
The question of whether or not sperm count is declining has been hotly debated for many years within the scientific community. However, no firm conclusion has been reached.
Of course, a reduced sperm count has important implications for reproduction, but this is not the only reason for alarm; low sperm count has been shown to increase the risk of all-cause mortality and morbidity.
Another general concern is that sperm count and other measures of semen quality might be a sign that we are living in a toxic environment. The more we understand about this, the better we can approach making informed changes to the chemicals that we use every day.
Gathering data on sperm count
With these factors in mind, a group of researchers recently set out to conduct a large-scale systematic review and meta-analysis of sperm count trends.
For the study, a group from the Hebrew University-Hadassah Braun School of Public Health and Community Medicine in Israel joined forces with the Icahn School of Medicine at Mount Sinai in New York City, NY. Their results are published this week in the journal Human Reproduction Update.
They screened 7,500 studies and completed a meta-regression analysis on 185 studies carried out from 1973 to 2011. The results were clear and surprising.
Men from Europe, North America, Australia, and New Zealand had a 52.4 percent decline in sperm concentration and a 59.3 percent decline in total sperm count.
In contrast, no significant decline was found in men from Asia, South America, and Africa - although there were fewer studies to analyze in these regions. Worryingly, the rate of decline in Western men did not appear to be slowing; "the slope was steep." Even when the analysis was limited to studies from 1996 to 2011, the trend was still significant.
The implications of reduced sperm count
Since 1992, the question of whether sperm count is steadily dropping has been widely debated. Although earlier studies have addressed this problem with varying results, the current research has a broader scope.
To ensure the analysis was as accurate as possible, the researchers controlled for a thorough array of potential factors. These included abstinence time, method of semen collection, how the sperm were counted, age of participant, how the study population was selected, and how many samples were given per man.
"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."
Lead author Dr. Hagai Levine
The authors believe that, because the decline is only seen in Western countries, "chemicals in commerce" may be playing a role in the downward trend.
Although the current study did not address the direct cause, decline in semen quality has been previously associated with pesticides, heat, lifestyle factors, diet, smoking, stress, and body mass index (BMI). The researchers ask whether the declining sperm count may be the proverbial "canary in the coal mine."
Because the study analysis was so detailed, and the dataset so varied - namely, it was spread evenly across 39 years and 50 countries - the findings are particularly robust, and they are, therefore, particularly worrying.
With connections already drawn between reduced sperm count and overall mortality, the authors write, "Research on causes and implications of this decline is urgently needed."