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  • According to a new study, the risk of older people developing Alzheimer’s disease over a one-year period nearly doubled following a COVID-19 diagnosis.
  • The highest risk was observed in women ages 85 and older.
  • Researchers aren’t sure whether COVID-19 triggers the development of Alzheimer’s disease or if it quickens its emergence.

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In a study published in the Journal of Alzheimer’s Disease, researchers at Case Western Reserve University School of Medicine found the risk of older people developing Alzheimer’s disease nearly doubled over a one-year period following COVID-19 infection.

Medical News Today spoke with Dr. Pamela Davis, the study’s co-author, a physician, and the Arline H. and Curtis F. Garvin Research Professor at Case Western Reserve School of Medicine. Dr. Davis said the research team elected to do this study because they were interested in COVID-19’s impact on the brain and wondered if older people who contract COVID-19 might be at a higher risk of developing Alzheimer’s disease.

“Many people believe that for Alzheimer’s disease there is a combination of factors that work together to give you the cognitive impairment, and we were concerned that the kinds of things that happened during COVID-19 — the intense inflammation, and perhaps the kinds of direct action on the brain of the of the virus — might be a risk factor,” Dr. Davis said. “So we went looking for that in our study.”

In 2021, Dr. Davis worked with a team of researchers on another study, which found that individuals with dementia had a greater risk of contracting COVID-19 and being hospitalized and dying from the disease than those without dementia.

Findings from the new study suggest that there may be “bidirectional relationships” between COVID-19 and Alzheimer’s disease.

For the study, the researchers used the TriNetX Analytics Platform, which provides clinical data and analytics, to access anonymous electronic health records of over 95 million people who made inpatient and outpatient visits at nearly 70 healthcare organizations. The participants came from 50 states and represented diverse geographic, age, race/ethnicity, income, and insurance groups.

Next, the researchers narrowed the list of participants to a group of 6.2 million adults ages 65 and older who had received medical treatment between February 2020 and May 2021 and had no prior diagnosis of Alzheimer’s disease.

Researchers then divided the participants into two groups: One group contracted COVID-19 between February 2020 and May 2021, and the other did not contract the disease during that time. About 5.8 million participants were in the group with no infection, while more than 400,000 had COVID-19.

The researchers looked at the risk for a new diagnosis of Alzheimer’s disease in the two groups as well as in three age groups (65 to 74, 75 to 84, and age 85 and older), men and women, and in Black, white, and Hispanic racial/ethnic groups.

Gender and age were the same in the COVID-19 cohort and the non-COVID-19 cohort. However, the group that contracted COVID-19 did include more Hispanic and Black participants and had a “higher prevalence of adverse socioeconomic determinants of health and comorbidities,” according to the study.

Cohorts were propensity-score matched for demographics, adverse socio-economical determinants of health, including problems with education, occupational exposure, physical, social and psychosocial environment, and known risk factors for Alzheimer’s disease. The researchers used a Kaplan-Meier analysis to estimate the likelihood of a new diagnosis of Alzheimer’s disease within 360 days after a COVID-19 diagnosis.

Researchers used Cox’s proportional hazards model to compare matched cohorts using hazard ratios and 95% confidence intervals.

Older people who had contracted COVID-19 had a higher risk — as much as 50 to 80% higher than the control group — of developing Alzheimer’s disease within a year.

The findings showed that the risk for developing Alzheimer’s disease in older people nearly doubled (0.35% to 0.68%) over one year following infection with COVID-19. The highest risk was observed in women ages 85 and older.

With this kind of study, Davis cautioned, “we can’t say that [COVID-19] causes the increased Alzheimer’s disease diagnoses.”

“We can say that they are associated, but we cannot infer causality,” she stressed.

Heather Snyder, Ph.D., vice president of medical and scientific relations at the Alzheimer’s Association, told MNT there could be a few explanations for the results of this study.

“First, the pandemic presented serious delays for individuals seeking out medical diagnoses like Alzheimer’s disease, meaning these results could be driven by those who already had Alzheimer’s disease when they were infected but had not yet sought out a formal diagnosis,” Dr. Snyder explained.

“Alternatively, COVID-19 infection — which is linked to immune changes, including inflammation — may impact the onset of brain changes that are linked to Alzheimer’s disease and other dementia,” said Dr. Snyder. “However, because this study only showed an association through medical records, we cannot know what the underlying mechanisms driving this association are without more research.”

Dr. Davis said more research needs to be done to understand any connections between COVID-19 and Alzheimer’s disease.

The Alzheimer’s Association hopes to begin answering some questions with its International SARS-CoV-2 Study, a network of studies aimed at understanding the long-term impact of SARS-CoV-2 on the brain.

“Because this virus is still relatively new, longitudinal research examining COVID-19 and dementia risk will take some time,” Dr. Snyder told MNT.

She said that her research team hopes to look at whether treatment of COVID-19 with antivirals mitigates the development of Alzheimer’s disease. She pointed out that the participants of this study had COVID-19 before these treatments were available.

In a 2019 study, researchers at Case Western Reserve University found patients who used anti-tumor necrosis factor agents for inflammatory diseases had a reduced risk of developing Alzheimer’s disease.

“So we would look we would want to look at whether those patients when they get [COVID-19] also have their [COVID-19] risk mitigated,” Davis said. “And that’s something that we can do relatively quickly in a retrospective study.”

Older individuals concerned about contracting COVID-19 and increasing their risk of developing Alzheimer’s disease should first and foremost make sure they have gotten COVID-19 vaccines and boosters, Dr. Robert John Sawyer, a neuropsychologist at Ochsner Health in Louisiana, told MNT.

Dr. Sawyer also recommended that concerned individuals focus their energy on reducing their risk of Alzheimer’s disease by making lifestyle changes.

“People are much more in control of other things like exercise, mental activity, diet, good sleep, getting your hearing fixed,” he told MNT. “And these things are much more likely to cause dementia than a mild case of [COVID-19].”

Dr. Davis recommended that older people who contract COVID-19 should also quickly contact their doctors to see if antiviral treatments are appropriate.

“If I were a prudent elder and I got [COVID-19], I would be very sure that I got a good antiviral agent in the hopes that reducing the body burden of virus and making the disease a bit milder might help mitigate the downstream effects,” she said.