Researchers are examining a connection between COVID-19 infection and an increased risk for developing Alzheimer’s disease. Although the link seems clear, the reasons behind it are not. What we know so far is based on several new studies.
In a 2022 study of more than six million people aged 65 and older, led by Case Western Reserve University in Cleveland, researchers found a 50% to 80% increased risk of Alzheimer’s in the year after COVID-19 infection, with the highest risk in women over age 85.
A separate Chinese study that recruited more than 3,200 COVID-19 survivors aged 60 and older found that long-term cognitive decline was common within six months to one year after infection.
And in St. Louis, researchers at the Washington University School of Medicine and the Veterans Affairs St. Louis Health Care system analyzed federal health data to study the post-COVID brain. They, too, noted an increased risk of Alzheimer’s disease among those infected with the virus.
“These results are worrisome,” said Case Western Reserve study investigator Pamela Davis, MD, PhD. “Alzheimer’s is very costly in terms of money, at over $300 billion a year, but is also extremely costly to families who are watching a loved one slowly slip away.”
What these findings mean
Although the connection is there, it’s not known whether COVID-19 causes, triggers, or accelerates the development of Alzheimer's disease.
One theory is that the connection is related to inflammation from the infection. The impact of COVID-19 on the brain is similar to that seen in Alzheimer’s disease. This inflammation could predispose someone who had COVID-19 to developing Alzheimer’s later in life, especially if they were seriously ill or had long-lasting symptoms.
A less concerning theory, however, is simply that getting care for COVID had increased the odds of detecting previously undiagnosed Alzheimer’s. In addition, isolation from friends, family, and community during the pandemic could have played a role in a person’s cognitive decline.
Dr. Davis also points out that the more than six million people in her study had been infected with the earliest – and most serious – version of the COVID-19 virus. It’s possible that later variants such as Omicron, which typically causes milder illness, may not have as much of an impact on dementia.
“We’re hoping this is a blip and not a trend,” she said.
It’s important to note that while the most common type of dementia is Alzheimer’s, there are other types, including Lewy body, vascular, and frontal lobe dementia. This study found a connection between COVID-19 and dementia in general, without specifying Alzheimer’s.
The role of infection
The concept that Alzheimer’s could result from an infection has been discussed for decades. Then COVID-19 came along – a never-before-seen virus with a wide range of symptoms affecting many parts of the body, including the brain.
There’s evidence that microscopic blood vessel injuries from COVID-19, as well as an attack on the brain by super-activated immune cells, are responsible for cognitive problems like severe headache, loss of taste or smell, and “brain fog.” Those brain injuries could lead to Alzheimer’s in the future.
In a study supported by the National Institute of Neurological Disorders and Stroke, the National Eye Institute, and the National Institute of Allergy and Infectious Diseases, researchers examined how COVID-19 affects the brains of mice and humans. They found that COVID-19 can change how some brain cells behave.
In a Canadian study, researchers studied the brains of people who died after COVID-19 infection. They found evidence of injuries to tiny blood vessels and a leakage of fibrinogen – leakage that’s also seen in Alzheimer’s disease.
Alzheimer’s typically takes years to manifest. It’s possible that people who are predisposed to developing Alzheimer’s may have that process sped up by COVID-19, putting them on a faster track to develop the disease.
Dr. Davis said a way to combat this risk is to take steps to avoid getting COVID-19 in the first place, including mask wearing and social distancing. For those who do get infected, she suggests getting immediate treatment with an antiviral medication such as Paxlovid, especially if they are at higher risk of getting seriously ill from the virus.
“Paxlovid wasn’t available at the time of our study,” she said. “We know that the virus itself can get to the brain and provoke an impressive inflammatory response, and that’s also a factor that goes into Alzheimer’s disease. If we could blunt the impact of the virus itself in terms of inflammation, we may have a better outcome.”
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