A prolonged decline in male fertility in the form of sperm concentrations appears to be connected to the use of pesticides, according to a study published Wednesday.
Researchers compiled, rated and reviewed the results of 25 studies of certain pesticides and male fertility and found that men who had been exposed to certain classes of pesticides had significantly lower sperm concentrations. The study, published Wednesday in Environmental Health Perspectives, included data from more than 1,700 men and spanned several decades.
“No matter how we looked at the analysis and results, we saw a persistent association between increasing levels of insecticide and decreases in sperm concentration,” said study author Melissa Perry, who is an environmental epidemiologist and the dean of the College of Public Health at George Mason University. “I would hope this study would get the attention of regulators seeking to make decisions to keep the public safe from inadvertent, unplanned impacts of insecticides.”
For decades, scientists have been trying to untangle puzzling questions over male fertility. Sperm concentrations are one of several factors that are a useful indicator. A report last year found that sperm counts were falling in every region of the globe and the pace of that decline was accelerating.
“There’s been some pretty, I’d say, convincing and sort of scary data on measures of male fertility over the previous 50-70 years, whatever it might be, from different places around the world suggesting sperm concentration is on decline and not just a little bit,” said John Meeker, a professor of environmental health sciences at the University of Michigan School of Public Health who was not involved in either of the recent studies. “It’s concerning.”
Scientists have long suspected changes to the environment could be contributing, and they’ve been probing the role of pesticides for decades in studies of animals and in human epidemiology research.
The new analysis focuses on two groups of chemicals — organophosphates and some carbamates — that are commonly used in insecticides. The researchers looked at data collected from groups of people with exposures to pesticides and others who were not. Most, but not all, of the research centered on exposures in the workplace. The researchers controlled for outside factors that could contribute to lower sperm counts like smoking and age.
“It was very well done, very carefully done, very comprehensive,” Meeker said.
Perry said researchers aren’t sure how pesticides are affecting sperm concentrations and more research will be needed.
It’s likely that pesticides are one of many environmental factors that could be contributing to a decline in sperm concentrations.
“The more you study something, the more complicated it seems to get, especially when it comes to biology and the human body,” Meeker said. “We’re slowly pointing out various chemicals or classes of chemicals we think could be harmful to something like reproductive health, but as far as a single smoking gun, I haven’t seen anything to that extent.”
The trend of sperm concentration declines has been widely observed in studies around the world, but it’s a complicated topic and some scientists still have reservations. Sperm are notoriously difficult to count and the technology to do so has changed over the years. There are many confounding factors that can affect male fertility, including age, obesity and opioid use, to name a few.
Sperm concentrations are one important data point to consider, but other factors — like how sperm are shaped and how they swim — are also critical to male fertility.
Perry said she hopes agencies like the Environmental Protection Agency begin to factor the impact of chemicals and pesticides on reproductive health in their assessments.
“Given the body of evidence and these consistent findings, it’s time to proactively reduce these insecticide exposures for men wanting to have families,” Perry said.
Evan Bush is a science reporter for NBC News. He can be reached at Evan.Bush@nbcuni.com.