A cold or stomach virus could worsen dementia in those suffering from Alzheimer's disease, research has revealed.
University of Southampton scientists found that the common infections and a rise in inflammation-like reactions in the brain were linked, resulting in an increased rate of cognitive decline.
The research studied the effect on the brain of inflammatory proteins released during an infection.
It found that those who were infected had double the rate of cognitive decline as those who were not.
The study, backed by the Alzheimer's Society, involved 300 people with mild to severe Alzheimer's disease and was published in Neurology.
The study's author, Professor Clive Holmes, said: "One might guess that people with a more rapid rate of cognitive decline are more susceptible to infections or injury, but we found no evidence to suggest that people with more severe dementia were more likely to have infections or injuries at the beginning of the study."
Dr Susanne Sorensen, head of research at the Alzheimer's Society, said: "We know there might be a link between inflammatory processes and Alzheimer's but this is not yet fully understood. These findings are helping us to understand more about possible reasons for this link."
She added that older people with dementia, and their carers, should treat infections seriously and seek medical advice.