Older adults infected with COVID-19 are at greater risk of developing Alzheimer’s disease in the coming year, according to a study of medical health records by researchers from Case Western Reserve University published this month in the Journal of Alzheimer’s Disease.

The risk was as much as 50% to 80% higher for those with COVID-19, compared to the control group in a study of more than 6 million patients 65 and older. The greatest risk was found in women and in those 85 and older.

Medscape noted that the risk of being diagnosed within a year with COVID-19 was “elevated in all age groups, regardless of gender or ethnicity.”

According to The Washington Post, “The results suggest researchers should be tracking older patients who recover from COVID to see if they go on to show signs of memory loss, declining brain function or Alzheimer’s disease. The study found that for every 1,000 seniors with COVID-19, seven will be diagnosed with Alzheimer’s within a year, slightly above the five-in-a-thousand diagnosis rate for seniors who did not have covid.”

In a news release, the researchers said that “the risk for developing Alzheimer’s disease in older people nearly doubled (.0.35% to 0.68%) over a one-year period following infection with COVID. The researchers say it is unclear whether COVID-19 triggers new development of Alzheimer’s disease or accelerates its emergence.”

It’s also possible, they said, that the interaction with the health care system makes diagnosis more likely.

“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 Pamela Davis, a research professor at the Case Western Reserve School of Medicine and the study’s co-author.

She said they looked for a connection because COVID-19 has been associated with inflammation and other central nervous system irregularities.

The group that had COVID-19 included more than 400,000 people, while the control group of non-infected people included 5.8 million people.

“If this increase in new diagnoses of Alzheimer’s disease is sustained, the wave of patients with a disease currently without a cure will be substantial, and could further strain our long-term care resources,” Davis said. “Alzheimer’s disease is a serious and challenging disease, and we thought we had turned some of the tide on it by reducing general risk factors such as hypertension, heart disease, obesity and a sedentary lifestyle. Now, so many people in the U.S. have had COVID and the long-term consequences of COVID are still emerging. It is important to continue to monitor the impact of this disease on future disability.”

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For the study, the researchers looked at de-identified electronic health records of 6.2 million adults who were 65 or older and who were treated between February 2020 and May 2021.

The downside to using the medical records, however, was no information was provided on the severity of symptoms from the coronavirus infection. And they did not differentiate those who had long COVID from those with typical COVID-19, Medscape said, as a medical code for long COVID had not been created before the study was completed.

An Alzheimer’s Association official urged caution in interpreting the results. “Because this study only showed an association through medical records, we cannot know what the underlying mechanisms driving this association are without more research,” Heather Snyder, the association's vice president of medical and scientific relations, told Medscape. “If you have had COVID-19, it doesn’t mean you’re going to get dementia. But if you have had COVID-19 and are experiencing long-term symptoms including cognitive difficulties, talk to your doctor.”

Gabriel de Erausquin, director of the Laboratory of Brain Development, Modulation and Repair at the University of Texas Health San Antonio, who was not involved in the research, also told The Washington Post that care was needed in interpreting findings.

“He cautioned that a diagnosis of Alzheimer’s disease is not necessarily confirmation of the disease. Doctors sometimes diagnose Alzheimer’s based on changes in behavior, or responses to a memory test. These are considered less accurate than imaging or spinal fluid tests that measure two types of proteins, beta-amyloid and phosphorylated tau, which accumulate abnormally in the brains of people with Alzheimer’s. Brain scans that look for structural changes, such as the shrinking of certain regions, are another more accurate indicator,” the article said.

In February, a smaller study from Columbia University found that some of the brains of patients who died of COVID-19 “display some of the same molecular changes found in the brains of people with Alzheimer’s disease.”

Though the study was very small and would need replication, the researchers noted that the changes “could help explain the memory problems reported by suffers of long COVID.” That study was published in Alzheimer’s & Dementia: The Journal of the Alzheimer’s Association.

Funding for the new study was provided by the National Institute of Aging, National Institute on Alcohol Abuse and Alcoholism, the Clinical and Translational Science Collaborative of Cleveland, and the National Cancer Institute.