A University of Washington study has found that wildfire smoke exposure may reduce sperm quality in men undergoing fertility treatment.
Researchers at UW Medicine examined semen samples from 84 men who provided sperm for intrauterine insemination procedures between 2018 and 2022.
Major smoke events from regional wildfires affected the Seattle area in 2018, 2020 and 2022, giving scientists a way to compare semen health before and during periods of heavy smoke.
“This study takes advantage of our institution’s location in the Puget Sound region, where wildfire smoke events create distinct pre- and post-exposure periods in a natural experiment to examine how a sudden, temporary decline in air quality influences semen parameters,” the authors wrote in the study, which was published in Fertility and Sterility.
The research found consistent declines in several key measures of sperm quality during wildfire smoke exposure.
Those included sperm concentration, total sperm count, total motile sperm count and total progressively motile sperm count.
One measure — the percentage of progressively motile sperm — showed a slight increase, but not enough to balance out the other declines.
Subjects served as their own controls in the retrospective analysis of medical records.
Results were consistent across multiple wildfire years, reinforcing the conclusion that the effects were not statistical outliers, according to the study.
“These results reinforce growing evidence that environmental exposures — specifically wildfire smoke — can affect reproductive health,” said senior author Dr. Tristan Nicholson, a reproductive urologist at UW Medicine’s Men’s Health Center and an assistant professor of urology at the University of Washington School of Medicine.
Nicholson noted that previous smaller studies, including work from Oregon Health & Science University, have also linked air pollution and wildfire smoke to impaired reproductive health.
“As we see more frequent and intense wildfire events, understanding how smoke exposure impacts reproductive health is critical,” she said.
Exposure to fine particulate matter in wildfire smoke has already been linked to health problems including respiratory issues, stroke, heart attack, lung cancer and cognitive impairment.
But scientists have not extensively studied the effects on male fertility.
The UW researchers stressed that further studies are needed to examine smoke exposure’s effects on reproductive age, sex differences, and couples attempting conception when one or both partners have experienced wildfire smoke.
While this study was not designed to evaluate pregnancy outcomes, the authors reported an 11% pregnancy rate and a 9% live birth rate among women whose partners participated.
Those results are similar to previously published data at the same fertility center.
One question still unanswered is whether sperm counts return to normal after exposure.
“We are very interested in how and when sperm counts recover after wildfire smoke exposure,” Nicholson said.
She added that her team is currently running a prospective pilot study of Seattle-area men to evaluate recovery patterns.
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