Professor David Melzer, who led the research team, said: “These initial results suggest that some risky pre-existing diseases in older people may have been overlooked.
“Our results suggest that (shielding) should be considered, as many people with dementia will have both the increased risks due to advancing age, plus the specific additional risk we have shown from having dementia as well.”
Around 850,000 people in Britain suffer from dementia, and there are currently no cures or treatments for the condition.
The researchers say the higher risk may be due to greater exposure to the virus – for example because they are in close proximity with other elderly people in care homes – or could be caused by the dementia disease process itself.
The team used results from 448 people aged 65 to 86 who tested positive for Coivd-19, predominantly while in hospitals at the peak of the epidemic in England, and compared them to 250,000 older people without coronavirus from the UK Biobank cohort, which tracks the health of participants over time.
They found heart disease and stroke were similarly common in people with and without Covid-19 after taking other background factors into account, suggesting these diseases are not especially risky.
Older men were at 80 per cent higher risk than older women, even when they did not have more pre-existing diseases. Black older people were more than three times more likely to be affected than white after accounting for the 15 pre-existing conditions studied.