COVID and the Brain: Should we be worried?
Read Time: Last Update: Mar 12Publish Update: Sep 20
Key takeaways
- COVID-19 infection can impact parts of the brain important for memory and smell.
- Certain brain diseases, such as psychotic disorders and dementia, show an increased risk for at least 2 years following COVID-19 infection.
- These changes are likely due to neuroinflammation, where the body’s immune system becomes activated and damages the brain.
- To reduce the risk of COVID-related brain disorders, it is important for everyone to get vaccinated and boosted against both COVID-19 and other infections, like the flu.
The COVID-19 pandemic has changed all of our lives during the last 2.5 years. Many of us have been infected by the virus at least once by now. Yet even after recovering from our illness, we may not be fully out of the woods. Emerging evidence suggests that even mild cases of COVID-19 can impact our brains in the long term. How worried should we be?
COVID Effects on Brain Structure
A major study on this topic came out in March 2022 in the journal Nature. A team of scientists from the University of Oxford analyzed brains of 785 participants aged 51 to 81. Each subject received two MRI scans a few months apart; around half of them developed COVID-19 between the scans.
The study found that the patients who developed COVID-19 had significantly thinner grey matter compared to those who were not infected. Grey matter is where the main “bodies” of brain cells live, whereas white matter holds the axons that connect each neuron to each other like a bundle of wires. This grey matter loss was strongest in two brain regions called the orbitofrontal cortex and the parahippocampal gyrus. These regions are important for both memory and the sense of smell.
The authors also reported that people who’d been infected with COVID-19 had reduced brain size overall, as well as greater cognitive decline between the two timepoints. This was true even when excluding patients who had been hospitalized with COVID, suggesting that event mild cases can impact the brain.
This study demonstrates that COVID infection alters the brain, but it does not address whether these changes had any noticeable or long-lasting impacts on people’s brain health. It also does not reveal why these changes occur. Let’s look to some other recent studies to answer these questions.
COVID and Brain Diseases
A recent study, published in The Lancet in June 2022, addressed the question of whether brain abnormalities in COVID-19 patients could impact their risk of brain diseases. The scientists (also from the University of Oxford) analyzed 89 million patient health records from the US and a few other countries. These patients were younger than in the previous study, with a median age of 42 years.
During the period of 2020-2022, 1.5 million of these patients were diagnosed with COVID-19. The study found that these patients were significantly more likely to develop a mood disorder, such as depression or anxiety, within 6 months of COVID-19 infection. However, these symptoms resolved to the same levels as the noninfected controls within 2 years, suggesting that mood disorders could be a transient result of infection.
However, the study also reported increased risk of psychotic disorders, cognitive deficits, dementia, or epilepsy which lasted at least 2 years post-infection. This was true for children as well, though their overall risk was smaller compared to adults. This result is troubling, as it suggests that certain forms of brain dysfunction can persist even years after mild COVID infection.
COVID and Neuroinflammation
Why are these changes occurring? Growing evidence suggests that neuroinflammation is at least partially to blame. Neuroinflammation is when the brain’s immune system becomes triggered by an infection or other challenge. In the process of fighting off the infection, immune cells can inadvertently damage your brain cells as well, which can contribute to a variety of neurological disorders.
A recent study published in the journal Brain demonstrated that neuroinflammation occurs with COVID-19 infection. Scientists from the National Institute of Neurological Disorders and Stroke performed autopsies on the brains of people who had died of COVID-19. They found signs of neuroinflammation, and particularly they observed that immune cells were attacking the cells of the blood-brain barrier, which can lead to increased risk of stroke.
Another paper, published in Cell, found that people with long-lasting cognitive symptoms after COVID-19 infection showed increased levels of inflammatory markers in their cerebrospinal fluid. The researchers also infected mice with a mild case of COVID-19. This resulted in neuroinflammation, as well as reduced production of new brain cells in the hippocampus (a brain region important for memory) and loss of myelin, a coating that allows neurons to transmit signals more quickly. Interestingly, the pattern appeared similar to the results previously observed following cancer chemotherapy; like COVID, chemotherapy has also been known to induce persistent “brain fog.”
Conclusion
Where do we stand on COVID and the brain? It’s likely that we will need to wait many years before we fully understand the long-term impacts of this virus. In general, though, we know that COVID-19 induces neuroinflammation; this is true of all infections, to some extent, but COVID-19 seems to be particularly good at triggering persistent neuroinflammation, which can have more dangerous consequences for the brain.
Most studies have focused on older adults, who seem particularly prone to infection-induced neuroinflammation. While children have lower risk overall, it remains unclear whether this will change as we have more years to observe the neurodevelopment of children post-COVID infection. Only time can tell the extent to which this pandemic will have long-term impacts on the health of our brains and bodies.
In the meantime, we should do everything we can to protect ourselves from this virus and minimize the rate of re-infection. Getting vaccinated and boosted against COVID-19 is critical, as it can reduce amount of inflammation that results from infection, which may be protective against brain disorders. This is particularly important for anyone at high risk for complications, such as anyone who is older, obese, or has certain medical conditions. Finally, be sure to get your annual flu shot; flu is another infection that can promote neuroinflammation, and becoming infected by both flu and COVID-19 might exacerbate potential complications.
