WASHINGTON — Former football players who had experienced more severe concussions were more likely to report erectile dysfunction and low testosterone than other players, according to a team of Harvard researchers.

Former athletes were more likely to report that doctors had recommended or prescribed treatments for the sexual health conditions if they had a higher “concussion symptom score,” a measure derived from self-reported head injury symptoms like dizziness and nausea, or if they reported more frequently losing consciousness playing football.  

“We found a very strong association between number of concussion symptoms and the likelihood that a former football player reported erectile dysfunction, or reported low testosterone,” Rachel Grashow, a research scientist at Harvard’s T.H. Chan School of Public Health and the study’s lead author, said in an interview. “As you increase the number of reported concussion symptoms, you see a subsequent increase in likelihood of ED or low T.” 

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It is the latest study to shed light on the long-term effects of playing football. Most research into football’s health impacts, however, has focused on future cognitive health problems, such as dementia and depression. It is the first study, the researchers said, to examine sexual health in a non-clinical setting in a large population of football players who suffered repeated brain injuries.

In the investigation, published Monday in JAMA Neurology, researchers used self-reported data about treatment for ED and low testosterone in 3,409 former players. More than 18% of the players reported low testosterone levels, 22.7% reported erectile dysfunction, and both rates rose in association with head trauma. Fewer than 10% reported undergoing treatment for both symptoms.  

While the investigators did not directly attribute the association to a specific physical injury, the paper cited damage to the pituitary gland often sustained during major injuries as a likely culprit for the linked sexual health problems.  

The association between overall concussion severity and loss of consciousness events remained strong even when researchers adjusted for external factors, including the players’ specific football position, body mass index, age, race, and self-reported use of prescription or performance-enhancing drugs. 

Numerous past studies have shown a link between brain trauma and sexual dysfunction. Those studies, however, were often tied to a single, severe incident such as a car crash or battlefield injury — not football injuries that were comparatively less life-threatening. Researchers also observed an association with sexual dysfunction regardless of how often a football player had experienced brain trauma. 

“We saw a statistically significant increase in risk of low testosterone even at relatively low numbers of reported concussion symptoms,” Grashow said, “which suggests that there may be no safe number of head hits.” 

Measuring the impact of comparatively more mild concussions is also instructive in the context of past research, said Dr. Daniel Daneshvar, a researcher who works at Boston University’s Chronic Traumatic Encephalopathy Center, which conducted the first large-scale brain health study in former NFL players. Daneshvar was not involved in the Harvard research. 

“We’re increasingly finding that the repetitive number of impacts are a better predictor of whether someone develops [chronic traumatic encephalopathy] as opposed to a limited number of more severe injuries,” Daneshvar said. CTE, a neurodegenerative condition that can impact mood and behavior, is among the most studied health effects of football-related brain injuries.   

The study also could also influence societal beliefs regarding football’s health impacts. The results of sustained brain damage are normally thought of as relating to depression, suicidality, and dementia. The Harvard investigation could expand society’s views of football-related brain injuries as causing not just cognitive health problems but physical health ones as well, Daneshvar said. 

“When we talk about CTE, we’ve largely been talking about problems related to behavior, to mood, to cognition,” he said. “But we know that traumatic brain injury has associations with issues throughout your entire body. We’ve found in multiple studies that there’s a relationship between pituitary problems and major traumatic brain injury.” 

The study authors cited numerous factors, including a reliance on self-reported health data instead of clinical assessments and potential recall bias, in acknowledging the paper’s limitations. 

Both Grashow and Danesvhar, however, said they viewed the correlation as stronger and more likely to be borne of a causal link because it remained consistent both when measuring overall concussion severity and reporting blackout incidents. Self-reported loss of consciousness events, Grashow said, were likely distinct and memorable, and therefore less subject to recall bias. 

Overall, Grashow called the findings “the strongest statistical relationship I’ll ever find in my career.”

The finding, she said, could have sweeping real-world implications, given the broader implications sexual health holds for quality of life and the fact that they often portend broader health issues. 

“If you’re a former player who had a head injury and you have ED, speak to your doctor,” Grashow said. “The hope is that we can undo some of the stigma associated with ED, that it’s a personal failure or failure of masculinity — there’s a real biological reason you’re experiencing this.” 

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