Athletes who receive repeated blows to the head could be at greater risk of developing dementia later in life, according to a new study.

Scientists said they have found the strongest evidence yet that repeated concussions could cause nerve-degenerative diseases like Alzheimer’s.

Professional rugby players and boxers are just two of the groups who may be suffering long-term damage from their chosen careers.

The study provides the first evidence that repetitive head trauma in collision sports could be linked to the development of a motor neuron disease

Researchers from the University of Rochester in New York studied autopsies of 12 athletes who died with brain or neurological disease.

All had a newly characterized disease called chronic traumaticencephalopathy, or CTE, in which dementia set in years after repeatedconcussions.

Three of the men were also diagnosed with ALS, a member of a familyof diseases called motor neuron disease, which cause progressivelyworse paralysis.

The researchers looked specifically for a protein called TDP-43.They found it in the brain and in the spinal cords of the men – whichcould explain the symptoms.

Scientists know that damaging one nerve can sometimes set off acascade of other nerves dying, for reasons that remain poorlyunderstood and TDP-43 could be involved.

Experts in brain injury said the study, published in the Journal of Neuropathology & Experimental Neurology, pointed to new areas of research and possible ways to prevent long-term damage from concussions.

‘If you could somehow give a person a drug, you could potentially prevent an illness like amyotrophic lateral sclerosis,’ commentor Dr Jeffrey Bazarian said.

Baseball players Lou Gehrig (left) and Babe Ruth at the Yankee Stadium in 1939. A link has been found between concussions and ALS also known as Lou Gehrig’s disease. The sportsman had this form of motor neuron disease.

The findings also point to an urgent need to monitor soldiers returning from Iraq and Afghanistan, many of whom suffer brain injuries from explosions, accidents and blows to the head.

‘This is the first pathological evidence that repetitive head trauma experienced in collision sports might be associated with the development of a motor neuron disease,’ said lead author Dr Ann McKee of Boston University School of Medicine.

Drugs including the hormone progesterone, monoclonal antibodies and the antibiotic minocycline are being studied to see if they can stop the process of nerve destruction that follows injuries such as a blow to the head or stroke.

David Hovda, director of the UCLA Traumatic Brain Injury Research Center, said: ‘I think it does is raise worries that individuals who had a career of exposure to repeat concussions … have a greater likelihood of developing motor neuron disease.’