COVID-19 can cause brain changes even in mild infections

The new study included about 400 middle-aged and older adults who underwent brain scans prior to coronavirus infection. UK BiobankA long-term health survey of 500,000 UK participants.

These people had a second brain scan after infection, most of them within 6 months of diagnosis. Most of these people showed mild to moderate symptoms, but 15 were hospitalized for COVID-19.

“96% of the participants were mildly infected, but the amount of gray matter was significantly reduced and the infected participants’ tissues were damaged,” said Douaud. statement.. “They also showed a greater decline in their mental ability to perform complex tasks, and this mental deterioration was partially associated with these brain abnormalities. These adverse effects. All became more pronounced as we got older. “

The researchers also included a second group of 384 people who were not infected with the coronavirus. This group was similar to the first group in terms of age, gender, ethnicity, and time between the two scans.

Comparing the changes in the brain that occurred over time in the two groups, we found that people infected with the coronavirus had greater loss of gray matter in the brain.

These changes were primarily in areas of the brain involved in the sense of smell. Another area affected is the area that plays a role in event memory.

Brain scans also showed signs of brain tissue damage in areas involved in the sense of smell.

In addition, the cerebrospinal fluid increased and the volume of the entire brain decreased. These changes suggest a broader loss of gray matter, in addition to the loss associated with areas directly related to the sense of smell, the researchers wrote.

They added that the structural changes in the brain were “moderately large.” The average reduction rate ranged from 0.2% to 2%.

In comparison, in the part of the brain called the hippocampus, the typical age-related annual loss of gray matter is about 0.2% in middle age and 0.3% in old age.

People infected with the coronavirus also performed poorly in cognitive tests that measure executive function and attention. The results were similar even if the researchers excluded those who were hospitalized.

However, this test is not a comprehensive assessment of thinking ability and memory.

Researchers emphasized that their results represent average changes. This means that not everyone infected with the coronavirus will experience similar changes in the brain.

In addition, the effects of infection on the brain may differ in younger people, as this study only includes middle-aged and older adults.

The survey results may not apply to other groups, as the majority of the subjects were also Caucasian.

Researchers suggest that the fact that many changes have occurred in areas related to odors in the brain may be due to the odor loss that occurred in many people infected with the coronavirus. ..

They write that lack of sensory input to the sensory-related areas of the brain, or inflammation of the sensory-related structures of the nervous system, may explain the loss of gray matter and other changes.

Loss of smell was a common symptom before the Omicron mutant. This study was conducted before the emergence of this variant.

The brain changes seen in this study require further investigation, but it is premature to know how concerned they are.

There are also many questions left. Is there a difference between those who are vaccinated and those who are not? Do all people who have lost their odor have similar changes in their brains? And can the brain recover from these changes?

“Whether this harmful effect can be partially reversed, or whether these effects are long-lasting, should be investigated with additional follow-up,” the researchers write.

previous study We found that olfactory training in people who lost their sense of smell was associated with an increase in gray matter in the parts of the brain involved in the sense of smell for reasons other than COVID.

Coronavirus infection is not the only condition or factor that causes this type of change in the brain.

one 2022 study Using data from UK Biobank, we found that air pollution was associated with a decrease in brain volume and an increase in white matter lesions. These types of lesions are associated with an increased risk of stroke and neurodegenerative diseases.

another 2021 study Published in The Journals of Gerontology, the Western lifestyle itself can lead to a significant reduction in brain volume with age compared to that found in indigenous peoples living traditional lifestyles. It suggests that there is.

Alcohol consumption is another factor that can affect the brain.recently study Even moderate drinking suggests that it is associated with a decrease in brain volume.

Like the recent COVID study, this was large and involved more than 36,000 adults.

This allowed researchers to take into account other factors that may affect brain volume, such as age, gender, obesity index, smoking status, socioeconomic status, and country of residence. ..

Even after adjusting for these factors, “the effect was seen in 90% of the brain region, including a significant reduction in gray and white matter throughout the brain.” Reagan R. WetherillPhD, Assistant Professor of Psychiatry, University of Pennsylvania, Perelman School of Medicine, and author of the 2021 study.

“For me, it showed that alcohol had a negative effect on the brain,” he added. “And it goes with preclinical literature investigating the effects of alcohol on the brain and body.”

Regarding the causes of brain changes associated with alcohol intake, Wetherill said there are studies suggesting that it is associated with oxidative stress, which damages brain cells.

other research We have discovered that inflammation may also be involved in alcohol-related brain damage. Oxidative stress and inflammation are interrelated and can affect the progression of the disease. Including COVID-19..

one study Hamsters suggest that inflammation of cells of the sensory system may be responsible for the odor loss seen in coronavirus infections.other research It suggests that the same mechanism may be involved in causing some of the symptoms of long COVID.

Wetherill said that oxidative stress and inflammation are common threads in many symptoms.

“These types of exposure show a lot of overlap with the viruses, toxics, or contaminants that the body is reacting to,” she said. “Chronic or severe exposure to these seems to have this negative effect on the body and brain.”

Studies on the effects of alcohol also suggest that the brain can recover from some of the damage caused by this type of chronic exposure.

“When a person with an alcohol use disorder is treated and has been abstaining from alcohol for about six months, neurogenesis is seen,” she said. “They have regained some of their brain volume and their cognitive function has improved.”

After the acute effects of infection have passed, additional long-term studies on COVID-19 patients are needed to determine if there is a similar rebound in brain health.

However, due to the COVID-related brain changes seen in some studies, scientists are concerned that the injury may later contribute to Alzheimer’s disease and dementia.

In response to this concern, representatives from the Alzheimer’s Association and more than 30 countries I participated together To study both the short-term and long-term effects of COVID-19 on the brain.