A bump on the head leading to momentary loss of consciousness may be linked to changes in the brain associated with Alzheimer’s, research suggests.

Protein accumulations in the brain called beta amyloid plaques, a hallmark of Alzheimer’s disease, were present at higher levels in people with memory problems who also had a history of trauma, scientists found.

On average, plaque levels were 18 per cent higher in individuals who during their lives had suffered a concussion resulting in at least a momentary loss of consciousness.

But this only applied to people with mild cognitive impairment, a relatively minor loss of memory and thinking skills.

Study leader Michelle Mielke, from the Mayo Clinic in Rochester, in the US, said: “Our results add merit to the idea that concussion and Alzheimer’s disease brain pathology may be related.

“However, the fact that we did not find a relationship in those without memory and thinking problems suggests that any association between head trauma and amyloid is complex.”

The researchers conducted brain scans on 448 people without memory problems and 141 with mild cognitive impairment in Minnesota, US.

Participants, all aged 70 or older, were asked if they had every suffered a brain injury that involved loss of consciousness or memory.

No difference in the brain scans was found between people without memory and thinking problems, whether or not they had experienced a head trauma.

The findings are published in the latest online issue of the journal Neurology.