Does COVID-19 shrink the brain?
by Health Desk | Published on June 3, 2022 – Updated on June 3, 2022 | Explainer
Recent research from the University of Oxford published in March 2022 studied the brains of 785 adult survivors of COVID-19 by taking brain scan images. The study found that these individuals had changes in the structure of their brains beyond what is usually expected with normal aging.
People in the United Kingdom study had two brain scans on average over a three-year period. Researchers used magnetic resonance imaging (MRIs) to get high quality images of volunteers' brains so they could compare them over time. Patients ranged in age from 51 to 81 with more severe changes occurring in older patients.
These images were examined for changes over time, and brain scans of people who went on to get COVID-19 were compared to those who did not get COVID-19 in the study period (the control group). The multiple images over time and the control group both helped researchers to isolate changes in the brain that were likely due to COVID-19 as opposed to normal aging.
Researchers found that changes to brain structure even occurred in people who had mild COVID-19. Brain tissue damage was most likely to occur in areas of the brain associated with smell, emotions, and memory.
While only a small handful of the patients in study were hospitalized and only two received critical care, the brains of patients in the study who had COVID-19 overall had a reduction in thickness or gray matter, a reduction in whole-brain volume, and an increase in cerebrospinal fluid volume (which puts pressure on the brain and is generally bad for the brain).
These changes were specific to COVID-19 survivors, even when compared to people who had other respiratory diseases. For example, these changes did not occur in people who had non-COVID pneumonia.
COVID-19 survivors also had weaker brain connections and showed poorer performance on thinking and memory tests. There may be some link between these changes in the brain and some of the symptoms frequently reported after COVID-19 both in the short and long-term, such as ‘brain fog.’
People who survived COVID-19 also showed brain-related abnormalities including a worsening of executive function, which is essentially “the management system of the brain” that impacts focus and organization. This worsening in executive functioning was found even in patients with mild symptoms.
The 348 people in the study who did not get infected with COVID-19 had brain scans that showed normal changes to the brain related to aging or respiratory diseases. Compared with the control group, the COVID-19 survivors on average had an additional 0.2% to 2% loss of gray matter or tissue damage between their 2 sets of scans.
While this isn’t a huge difference, it is still an important finding. For context, adults normally lose about 0.2% to 0.3% of gray matter in memory-related brain regions each year. This means that compared to people who didn’t get COVID-19, survivors of COVID-19 lost one to six years’ worth of brain matter. The impacts on the brain were worse for older study participants. More research is needed to better understand the impacts of COVID-19 in the brain in the short to long-term.
Context and background
Brain fog has been a reported symptom of COVID-19 since the start of the pandemic. We also had an early understanding that the virus that causes COVID-19 likely impacts organs, including the brain. As a result, it’s important that researchers study the impact of COVID-19 on the brain which is what this study aimed to do.
While this study found more brain damage overall in people who had COVID-19 compared to people who didn’t, this does not mean that every person who has been infected with COVID-19 will have changes happen to their brain. This study established a likely link between COVID-19 and brain damage on average, meaning 1) more research is needed to help us establish a causal lin k and understand how much the virus is actually directly leading to any brain damage, and 2) not each individual person will experience brain damage from COVID-19.
It is also currently unclear if any changes to the brain are long-term or can be reversed. More research is needed.
One limitation in the study is that no information about symptoms or experiences with long COVID were obtained, so scientists have been unable to link brain changes to specific symptoms or long-lasting impacts of the virus. Information about vaccination status was also not known or factored into the study.
Changes in the brain following COVID may have occurred for numerous reasons including inflammation, degeneration through certain pathways, or sensory deprivation. Further research will help us to understand brain changes that are connected to the virus itself and not these other potential causes.
- Even Mild COVID-19 May Change the Brain (JAMA)
- SARS-CoV-2 is associated with changes in brain structure in UK Biobank (Nature)
- Even mild COVID can cause brain shrinkage and affect mental function, new study shows (Gavi)
- Study reveals some brain changes, even in mild COVID-19 (CIDRAP)
Used with Permission from Health Desk, a public health hub that explains emerging COVID-19 science.