"DNA integrity is crucial to normal fertility," Tanrikut said. For example, increased DNA fragmentation of sperm increases the risk of failure of intrauterine insemination.

"Abnormal sperm DNA integrity even affects pregnancy outcomes of the most advanced assisted reproductive technologies, such as in vitro fertilization (IVF)," she added. "In fact, it is the only male factor finding that has been shown to affect intracytoplasmic sperm injection (ICSI) results."

"A large proportion of patients on (SSRIs) may have their fertility affected," co-investigator Dr. Peter N. Schlegel, at Weill Medical College of Cornell University in New York, observed in correspondence with Reuters Health.

Among infertile men taking an SSRI, "a standard semen analysis won't measure this effect," Schlegel pointed out, and "a special test for DNA fragmentation...should be considered."

The sperm appears to be damaged by a slowing down of their transport through the body, "a novel mechanism of damage," he said. "Most agents affect fertility by knocking down sperm production. Slowing down sperm transport can allow sperm to be damaged (by higher temperatures, or just 'getting too old' – being ejaculated after they should have been)."

"We have seen severe cases where the sperm are slowed down so much that almost no sperm appear in the ejaculate."

Based on these findings, the research team is planning larger studies using other SSRI antidepressants.