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Serious head injuries nearly double a person’s risk of developing dementia. That’s the message from an analysis of over 40,000 people who sustained some kind of head injury between 1986 and 2014.

Half the people in the study had moderate-to-severe head injuries, which cause lesions in the brain and require a person to stay in hospital for three days or more. The other half had milder head injuries with no lesions, and were able to go home within a day.

Comparing the longer-term health of these two groups revealed that the risk of developing non-Alzheimer’s dementia is 90 per cent higher in those with moderate-to-severe injuries, says Rahul Raj at the University of Helsinki, Finland. This was the case even after taking factors like education and socioeconomic status into account, he says.


Middle-age effect

In all, 696 of the 19,936 people with severe head injuries went on to develop dementia, while only 326 of the 20,703 people with milder injuries did the same. The risk of dementia was highest in people who sustained severe, traumatic head injuries between the ages of 41 and 50.

Previous studies have found that blows to the head can raise a person’s likelihood of dementia, as can highly physical sports. “This large study adds to prior published work indicating that a history of traumatic brain injury significantly increases the risk for dementia,” says Alan Faden at the University of Maryland School of Medicine, who last year discovered that blows to the head cause tiny, mysterious particles to migrate across the brain.

The growing evidence that head injuries increase the risk of non-Alzheimer’s dementia may be down to the effects of chronic brain inflammation caused by head trauma, says Faden.

Journal reference: PLoS Medicine, DOI: 10.1371/journal.pmed.1002316