The study from University of Southampton, UK, has revealed that people who had respiratory, gastrointestinal or other infections or even bumps and bruises from a fall were more likely to have high blood levels of tumour necrosis factor-a, a protein involved in the inflammatory process.
And were also more likely to experience memory loss or other types of cognitive decline than those who did not have infections or had low levels of the protein.
During the study, the researchers examined cognitive abilities of 222 people with Alzheimer's disease with an average age of 83.
The findings revealed that people who had high levels of the protein in their blood had memory loss at four times.
In addition, those with high levels of the protein at the start of the study also experienced acute infections during the study had memory loss at 10 times the rate of those who started with low levels and had no infections over the six-month period.
"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," said study author Dr Clive Holmes, MRCPsych, of the University of Southampton in the United Kingdom.
"More research needs to be done to understand the role of tumor necrosis factor-alpha in the brain, but it's possible that finding a way to reduce those levels could be beneficial for people with Alzheimer's disease," Holmes added.
The study appears in journal Neurology, the medical journal of the American Academy of Neurology.