Older people who were infected with COVID-19 show a substantially higher risk as much as 50 per cent to 80 per cent higher than a control group of developing Alzheimer's disease within a year, warns a new study.

The study, published in the Journal of Alzheimer's Disease, indicated that people 65 and older who contracted COVID-19 were more prone to developing Alzheimer's disease in the year following their COVID-19 diagnosis. And the highest risk was observed in women at least 85 years old.

The findings showed that the risk for developing Alzheimer's disease in older people nearly doubled (0.35 per cent to 0.68 per cent) over a one-year period following infection with COVID-19.

"The factors that play into the development of Alzheimer's disease have been poorly understood, but two pieces considered important are prior infections, especially viral infections, and inflammation," said researcher Pamela Davis from the Case western reserve university.

"Since infection with SARS-CoV2 has been associated with central nervous system abnormalities including inflammation, we wanted to test whether, even in the short term, COVID-19 could lead to increased diagnoses," she added.

For the study, the team analysed the anonymous electronic health records of 6.2 million adults 65 and older in the US who received medical treatment between February 2020 and May 2021 and had no prior diagnosis of Alzheimer's disease.

They then divided this population into two groups: one composed of people who contracted COVID-19 during that period, and another of people with no documented cases of COVID-19. More than 400,000 people were enrolled in the COVID-19 study group, while 5.8 million were in the non-infected group.