Men who carry cell phones in their pant pockets could be weakening their ability to bear children because they’re exposing sperm cells to potentially damaging radiation, suggested findings published in the journal Environment International and reported by Medical News Today.

For the study, researchers at Exeter University in the United Kingdom pooled data from nearly 1,500 semen samples collected at fertility clinics and research centers around the world. Next, scientists checked sperm movement (a.k.a. motility), concentration and proportion within the samples and ran the results alongside potential environmental factors.

Findings showed that men who had been exposed specifically to cell phones had, on average, an 8 percent reduction in both the proportion of live sperm in their semen, and their sperm’s ability to swim toward an egg. Scientists said the findings “strongly suggest” that men’s exposure to radio-frequency electromagnetic radiation (RF-EMR) emanating from their cell phones could be responsible for their having poor quality sperm. What’s more, researchers noted that the results were consistent for men in a laboratory setting and men in the general population.

Researchers are concerned because a growing percentage of couples in high- and middle-income countries—where cell phone ownership is common—have trouble conceiving kids. In addition, some places show a mysterious reduction in men’s semen quality. Studies show eating large quantities of fatty red meat could also damage a man’s sperm quality.