A Covid infection can triple the rate of brain degeneration in middle-aged and older people, a world-first study suggests.

University of Oxford researchers looked at brain scans of more than 400 people between the ages of 51 and 81 before and after they had the disease. 

Results showed that in olfactory-related regions, responsible for smell, their brain volume shrunk by an average of 0.7 per cent compared to a control group who did not get Covid. 

A middle-aged person would normally expect to lose about 0.2 per cent volume in that area per year, while an older person could expect to see a 0.3 per cent decrease.

On average, Covid patients involved in the study had four months between their two scans — suggesting the virus significantly speeds up the rate of degeneration.   

Survivors also took longer to complete cognitive tests and achieved poorer scores compared to their peers.

To check that the declines in brain matter and cognition could not have been replicated by any respiratory illness, the researchers carried out an analysis of the brains of pneumonia patients and found no similar changes.

The study may help explain why many people continue to suffer brain fog and other neurological issues months after clearing a Covid infection. 

Oxford scientists said the reduction in brain volume was more pronounced among older people and the 15 patients who were hospitalised with the disease.

But declines were still evident in patients who had mild to moderate Covid or were asymptomatic.