The legacy of head knocks in elite football players appear to go beyond neurological damage with new research finding a link to low testosterone and erectile dysfunction (ED).

US researchers said concussion associated hypopituitarism may explain the association between concussion with low testosterone levels and ED.

A survey of 3,409 former professional US football players found those who reported multiple concussion symptoms during their football career were more likely to have been recommended or prescribed medication for low testosterone or ED.

Of the respondents, who had a median age of 52 years at the time of the survey, 18.3% reported low testosterone levels, 22.7% reported ED and 9.8% reported both.

About 40% of men reporting low testosterone and 50% of men reporting ED were currently taking relevant medications such as testosterone replacement therapy and phosphodiesterase type 5 inhibitors.

The study, published in JAMA Neurology, found a robust and increasing association between concussion symptoms including headaches, nausea, dizziness, confusion, memory problems, seizure and loss of consciousness and self-reported low testosterone and ED.

“Even participants with relatively few concussion symptoms (ie, those in the second quartile) had significantly elevated odds of reporting low testosterone levels compared with men in the lowest quartile,” the study authors said.

“Acceleration and deceleration forces can shear axonal tracts that connect the pituitary to the hypothalamus. Thus, the combination of intracranial pressure, reduced blood flow, and diffuse axonal injury between the pituitary and the hypothalamus could cause diminished pituitary function, leading to low testosterone levels and ED.”

The findings support other evidence linking single head injuries with pituitary dysfunction in the general population, professional boxers and war veterans.

Associate Professor Michael Buckland, head of neuropathology at the Royal Prince Alfred Hospital, told the limbic that vascular or nerve injury impacting the pituitary were both possible.

“The vessels that supply the pituitary are quite long and prone to injury. The other thing is it could be a nerve fibre injury because there are lots of nerve fibres from the hypothalamus down to the pituitary,” he said.

Unifying hypothesis with CTE

“It might be that those fibres are prone to injury with multiple concussion and that certainly fits with chronic traumatic encephalopathy (CTE).”

He said it is thought that nerve fibre injury might release the tau that accumulates in CTE.

“It may be that the tau we see in the early stages is really just telling us that there has been significant axonal injury or nerve fibre injury underneath.”

Associate Professor Michael Buckland said the study was a reminder that clinicians always had to treat the whole person.

“There are systemic effects of repetitive head injury rather than just cognitive decline.”

He said research questions related to the long-term sequelae of multiple concussion in sport included the incidence or prevalence of CTE and the additional risk factors that meant one player would develop CTE when others didn’t.

“A third one would really be more research into the effects of head knocks in the developing brain because there is evidence to indicate that children who play contact sports before the age of 12 have earlier age of onset of CTE and more severe CTE.”

“So there seems to be a vulnerability period in the young and we need to understand that more because we should really be thinking about modifying sports for kids.”