Over the past 40 years, sperm counts in men from North America, Europe, Australia, and New Zealand have dropped by over 50 percent, researchers announced on Tuesday.
Researchers examined 7,500 studies conducted between 1973 and 2001. They selected 185 studies with consistent counting methods and performed analyses on data from almost 43,000 men.
Their findings, released in Human Reproduction Update, showed that sperm concentration fell from 99 million per milliliter to 47.1 million per milliliter during the span of the study, indicating a 52.4% decline in sperm concentration and a 59.3% decline in total sperm count for men in these nations. What’s more, the scientists found that the decrease in sperm count is not slowing. As sperm counts have implications for morbidity and mortality, these results raise potential concerns for health and fertility.
While previous studies on sperm count were criticized for not accounting for confounding variables like age, sexual activity, or infertility, this study used consistent sperm count methods and broad data sets from many locations to address these concerns.
The study did not directly address causes for the decline, though in interviews with New Scientist, study author Shanna Swan of the Icahn School of Medicine at Mount Sinai indicated that since the decline occurred in these specific nations, there may be a causal relation with chemicals. The impact of chemicals, like phthalates that are often found in food packaging and make their way into nearly every brand of macaroni and cheese, has been called into question lately by data that suggests they may interfere with testosterone production and endocrine systems.
Here’s Kate Kelland, reporting for Scientific American:
“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,” said Hagai Levine, who co-led the work at the Hebrew University-Hadassah Braun School of Public Health and Community Medicine in Jerusalem.
The analysis did not explore reasons for the decline, but researchers said falling sperm counts have previously been linked to various factors such as exposure to certain chemicals and pesticides, smoking, stress and obesity.
This suggests measures of sperm quality may reflect the impact of modern living on male health and act as a “canary in the coal mine” signaling broader health risks, they said.
But it’s not all bad news—47.1 million sperm per milliliter is still well above the 15 million sperm threshold that is considered low from a fertility standpoint. The study revealed no clear decline in sperm count for men in South America, Asia, or Africa, but the authors note that far fewer studies have been conducted in these regions.
For now, the question of what is causing sperm count decline is still open, but the evidence of the trend is increasingly apparent.