For some, coronavirus-like symptoms linger for weeks or months after their initial infection subsides. Experts call the condition long COVID-19, and it’s been known to affect nearly every organ in the body.
Research shows thousands of long-COVID-19 patients report feeling “brain fog,” a non-scientific term used by some people to describe their sluggish or fuzzy minds. Now, a new study adds to the growing body of evidence on the topic.
Research on 740 people who were experiencing long COVID-19 an average of seven months after their infection cleared found the most common problems involved memory encoding (24%) and memory recall (23%), according to a study published Oct. 22 in the journal JAMA Network Open.
Memory encoding is the initial learning of information, such as learning a new recipe by repeating it out loud to yourself. Memory recall is remembering information you learned in the past, such as recalling the section of the car garage you parked in.
The next most common cognitive issues reported among long-COVID-19 patients were category fluency (20%, the ability to think of words within a specific category, such as colors), processing speed (18%, the time it takes for someone to complete a mental task, such as breaking when they see a stop sign), executive functioning (16%, the ability to focus, follow directions and handle emotions) and phonemic fluency (15%, the ability to think of words that start with a specific letter).
Researchers also found people who were hospitalized while battling COVID-19 were more likely to have cognitive problems than those who were not.
Participants were enrolled in a Mount Sinai Health System registry in New York between April 2020 and May 2021. They were an average age of about 50 and had no history of dementia. Researchers adjusted their findings for race, ethnicity, smoking status, body mass index, depression and other health conditions.
A separate study published in February showed 81% of 57 hospitalized yet recovering COVID-19 patients had cognitive impairment, including in working memory, divided attention and processing speed.
It’s important to note that infection severity does not always determine if someone will develop long-COVID-19.
A study from June of nearly 2 million coronavirus patients across the country found that about a quarter developed at least one long-COVID-19 symptom such as brain fog, breathing difficulties or high cholesterol 30 days or more after initially testing positive.
However, 19% who never felt sick during their infection later became a long-hauler, as those who go on to experience persistent symptoms for more than four weeks after diagnosis have come to be called. Meanwhile, about 28% of those who had symptoms but were not hospitalized and 50% of patients who were admitted to the hospital went on to develop long-COVID.
Why does COVID-19 cause brain fog?
In some cases, the coronavirus finds ways to directly affect the brain via inflammation, stroke or blocking oxygen flow.
But the virus could also indirectly attack the brain through other symptoms such as fatigue, body aches, headaches and difficulty sleeping, which can all cause brain fog, according to Dr. Andrew Budson, a cognitive behavioral neurologist at the Veterans Affairs Boston Healthcare System.
“For example, how can you think clearly if you’re feeling fatigued and your body is aching? How can you concentrate if you were up half the night and awoke with a headache?” Budson wrote for Harvard Health Publishing in March.
The researchers of the new study said their findings are “generally consistent” with those on other viruses, such as influenza, that are also known to cause cognitive issues. Inflammation is likely to blame, experts say.
“What we’re seeing with COVID-19 is similar to infectious complications we’ve seen with other viruses, such as SARS and H1N1,” Dr. Rachel Zabner, an infectious disease specialist and co-director of Cedars-Sinai’s COVID-19 Recovery Program, said in an April blog post. “With COVID-19, there’s an activation of the immune system that persists for months, which can affect neural connections in the brain. The stress of navigating COVID-19 — constantly being in ‘fight mode’ — can affect brain function, too.”
There are no tests or scans that can diagnose someone with long-COVID-19 brain fog, so doctors have to rely on patients’ reports of symptoms such as dizziness, fatigue, memory loss and decreased attention span. In severe cases, some people may experience hallucinations or mood disorders.