A bump on the head can double the risk of getting dementia, even if you do not lose consciousness, researchers have warned. Picture: Pexels

A bump on the head can double the risk of getting dementia, even if you do not lose consciousness, researchers have warned.

More than two-thirds of traumatic brain injuries in England and Wales are classed as ‘mild’. Often caused by falls or minor car crashes, these cases can go unreported because victims fail to realise they have suffered a significant injury.

But a study of more than 350,000 people has found such blows to the head raise the risk of getting dementia by more than double, and the risk is similar to that of being knocked unconscious.

Researchers led by the University of California in San Francisco tracked Army veterans who had suffered blows to the head both in military and civilian life for an average of just over four years. Dr Kristine Yaffe, a senior author of the study, said: ‘There are several mechanisms that may explain the association between traumatic brain injury and dementia.

‘There’s something about trauma that may hasten the development of neurodegenerative conditions. One theory is that brain injury induces or accelerates the accumulation of abnormal proteins that lead to neuronal death associated with conditions like Alzheimer’s disease.

‘It’s also possible that trauma leaves the brain more vulnerable to other injuries or ageing processes, but we need more work in this area.’

More than 10,000 people in England and Wales suffered a mild traumatic brain injury between April 2014 and June 2015.

Brain injuries are most common in people aged between 80 and 90, who are vulnerable to falls, and also peak in those aged 20 to 30, who suffer around 15 per cent of these injuries, often from traffic collisions. Traumatic brain injuries do not always cause concussion and a mild brain injury often does not cause loss of consciousness, but can cause temporary amnesia for up to a day.

To look at the effect of the injuries, the US researchers matched 178,779 military veterans who had suffered traumatic brain injuries with an equal number who had not. They found someone’s risk of dementia almost quadrupled if they had suffered a moderate to severe brain injury.

But a brain injury without loss of consciousness raised the risk by 2.36 times, which is similar to the 2.51 times increased risk for people who lost consciousness. The study included veterans whose head injuries could have taken place at home, as well as veterans from Iraq and Afghanistan, who were more likely to have been injured in combat zones, including through shockwaves from explosions.

The study’s lead author, Dr Deborah Barnes, said: ‘The findings in both groups were similar, indicating that concussions occurring in combat areas were as likely to be linked to dementia as those concussions affecting the general population.’

The findings were published in the journal JAMA Neurology.