COVID-19 raises risk of developing Alzheimer’s disease by 50-80% in older adults

In a recent study published in the Alzheimer’s Disease Journalresearchers in the United States investigated whether severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections could trigger the development of a new Alzheimer’s disease (AD)

It has been suggested that infections can lead to the development of AD; however, it is unclear whether SARS-CoV-2 infections may increase AD risk. The increased risk of SARS-CoV-2 infections in patients with Alzheimer’s disease and the long-term neurological sequelae of coronavirus disease 2019 (COVID-19) (in part representing changes associated with the inflammation, which are central in the neurological pathophysiology of Alzheimer’s disease) indicate a two-way one-way relationship between SARS-CoV-2 infections and Alzheimer’s disease. The study authors previously showed a high risk of breakthrough SARS-CoV-2 infections in fully vaccinated AD patients.

Study: Association of COVID-19 with new-onset Alzheimer’s disease. Image Credit: Donkeyworx/Shutterstock

About the study

Researchers examined the risk of new onset Alzheimer’s disease in SARS-CoV-2 positive patients in this retrospective cohort study.

The study included 6,245,282 adults aged ≥65 years with no prior diagnosis of AD. Data was obtained from anonymized EHRs (electronic health records) of more than 95 million SARS-CoV-2 positive patients during outpatient and inpatient visits to healthcare organizations (n=68) in 50 United States (USA) covering different geographic, race, age, insurance and income groups.

Study participants were categorized into two groups: (i) the SARS-CoV-2-positive group comprising 410,748 people who acquired SARS-CoV-2 infections between February 2, 2020 and May 30 2021; (ii) the SARS-CoV-2-negative group comprising 5,834,534 people not exposed to SARS-CoV-2 but who sought medical care from health organizations between February 2, 2020 and May 30, 2021 for medical reasons not related to COVID-19.

AD and SARS-CoV-2 infection status was based on ICD-10 (international classification of diseases) codes and laboratory tests. The risk of recent-onset AD was examined for both groups stratified by race (Hispanic-Caucasian and Black-Caucasian) and age (65–74, 75–84, and ≥85).

Propensity score matching (PSM) was performed in a 1:1 ratio for demographic parameters and adverse socioeconomic determinants of health such as educational difficulties, occupational exposures, social, physical environments or psychosocial and factors known to increase AD risk. The team used Kaplan-Meier estimator and Cox proportional modeling to analyze and calculate hazard ratios (HR).

Results

After PSM, the data showed that the average age of individuals in both study groups was 74 years, most of whom were female (54%). The average proportions of black, white, and Hispanic were 10%, 75%, and 6.7%, respectively, and adverse socioeconomic and psychosocial circumstances were reported for 13% of the sample population.

Comorbid conditions such as hypertension, obesity, type II diabetes, depression, hearing loss, traumatic brain injury, smoking and heavy alcohol consumption were prevalent in 60%, 23%, 30 %, 22%, 5.8%, 3.1%, 11% and 3.8% of the sample population, respectively.

Prior to PSM, the odds of new AD occurrence in SARS-CoV-2 positive and SARS-CoV-2 negative individuals were 0.7% and 0.4%, respectively. After PSM, the risk increased in SARS-CoV-2 positive people compared to SARS-CoV-2 negative people (HR: 1.7).

HR values ​​for risk of new-onset AD in COVID-19 patients aged 65-74, 75-84, and ≥85 years were 1.7, 1.6, and 1.7, respectively . HR values ​​for risk in women (HR 1.8) were higher than those in men (HR 1.5). HR values ​​for risk among blacks, whites, and Hispanics were 1.6, 1.6, and 1.3, respectively. Taken together, the risk was highest in adults aged ≥ 85 years (HR 1.9) and in women (HR: 1.8).

Overall, the study results showed that adult SARS-CoV-2-positive women aged ≥85 years had a significantly higher risk of new onset of AD within 360 days of AD diagnosis. infection with SARS-CoV-2. However, future studies are needed with validation of data from multiple sources and longer follow-up periods to elucidate the mechanisms and for continued monitoring of the impact of SARS-CoV-2 infections on AD.

Study limitations

Limitations of the present study include the retrospective and observational nature of the study which could introduce potential biases and inaccuracy in the diagnosis of AD, which may not have significantly affected the relative risk analyzes since both groups were formed from the same data set.

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