Low testosterone is not something most people typically associate with NFL players.
But repeated concussions from professional football appear to be damaging the sex life of players, causing erectile dysfunction and lowering their levels of the male hormone, a new study claims.
"The guys at the highest level of concussion were almost twice as likely to report erectile dysfunction as the guys with the lowest levels," said senior study author Andrea Roberts, a research scientist with the Harvard T.H. Chan School of Public Health in Boston. "We found as concussion symptoms increase, the risk of ED and low testosterone increased right alongside."
Repeated concussions could be doing damage to parts of the brain that regulate hormone levels and sexual activity, the researchers speculated.
However, only an association and not a cause-and-effect link was observed, and other experts noted that other effects of head injury also can increase the likelihood of impotence, including increased stress, poor sleep, high blood pressure and other issues with brain function.
"Those are all a constellation of factors that relate to ED," said Jay Alberts, a concussion researcher and chair of the Cleveland Clinic's Lerner Research Institute. He wasn't part of the study.
For the research, Roberts and her colleagues surveyed more than 3,400 former NFL players, representing the largest-ever pooled study group of former pro football players.
Participants were asked about specific concussion symptoms, including how often blows to the head or neck caused them to:
They were also asked whether a doctor had recommended medication for either low testosterone or erectile dysfunction, and whether they were taking such drugs.
Of all participants, 18% reported low testosterone and nearly 23% reported ED. Slightly less than 10% of participants reported both.
Players who reported the highest number of concussion symptoms were 2.5 times more likely to have been recommended medication for low testosterone, compared with men who had the fewest symptoms.
They also were nearly twice as likely to report a recommendation for ED medication, researchers found.
What's more, players who lost consciousness following head injury were at higher risk of erectile dysfunction even if they didn't experience any other concussion-related symptoms.
The link between concussion and ED was present among both older men and younger players under age 50, and it persisted over time.
Roberts noted that even players with the lowest number of concussion symptoms had an increased risk of low testosterone, suggesting there may be no safe threshold for head trauma. About 1 in 5 players with the lowest levels of concussion had low testosterone levels.
The researchers think this problem might be tied to the pituitary gland, the "master operator in terms of a lot of hormones in your body," Roberts said.
"Your brain kicks off the signal to adjust both your testosterone level as well as your sexual function," Roberts said. "That's the thing we suspect is being damaged by these blows to the head."
The findings "suggest concussions are a risk factor for ED and low testosterone, even for younger guys," Roberts said.
However, Alberts said men who've experienced a single concussion in their lives probably shouldn't worry, especially if the concussion didn't require hospitalization.
"It would be hard to imagine a single impact like that would trigger significant events or ED," Alberts said.
The findings were published Aug. 26 in the journal JAMA Neurology.
Dr. Sam Gandy, director of the Mount Sinai Center for Cognitive Health and NFL Neurological Care, reviewed the study and agreed that the pituitary gland is a strong suspect here.
"Pituitary damage has long been associated with concussion, and often pituitary function is one of the first thing physicians check once concussed patients are stable," Gandy said.
In fact, Gandy said low testosterone levels caused by concussion might be contributing to dementia and brain function problems found in players.
Previous studies have found that men who undergo chemical castration to treat prostate cancer experience a roughly doubled risk of dementia, Gandy said. They also have an increase in blood levels of amyloid, a protein linked to Alzheimer's disease.
"This illustrates the close relationship between male gonadal hormones and brain function, and suggests that testosterone supports cognition and memory at some level," Gandy said.
The Mayo Clinic has more about concussion.