For most, COVID-19 causes a few days of mild to moderate symptoms, but other feel the effects for months. Some of these effects are neurological, leading scientists to ask whether COVID-19 could increase the risk of dementia. Medical News Today looked at the evidence and spoke with experts to find out the latest views.
Since the start of the COVID-19 pandemic, more than 425 million SARS-CoV-2 infections have been confirmed worldwide. Globally, almost 6 million people have died from, or with, the infection.
For most, when SARS-CoV-2 infection leads to COVID-19, the symptoms are mild to moderate. But for some, symptoms of the illness are prolonged.
have described this issue, long COVID, as not recovering [for] several weeks or months following the start of symptoms that were suggestive of COVID, whether you were tested or not.
Symptoms of long COVID vary, but some are common COVID-19 symptoms, such as fatigue, shortness of breath, a cough, and joint pain.
Other respiratory virus infections have been associated with neurological and psychiatric after-effects. The authors of one review
observe that Numerous respiratory viruses can infect the cells of the peripheral and central nervous systems, elicit inflammatory cascades, and directly and indirectly cause various neurologic manifestations.
And it seems that COVID-19 is no exception, with many people reporting neurological symptoms after SARS-CoV-2 infections. These symptoms may include:
- brain fog, a reduced ability to think clearly
- difficulties with memory and concentration
- difficulty sleeping
- changes in mood
Experts are now investigating how COVID-19 might affect neurocognitive function and whether it may increase dementia risk.
SARS-CoV-2 usually gains access to the body via droplets that enter the nose or mouth. From there, the virus moves to the throat. It can then travel to the lungs and other organs, and, various studies suggest, may enter the nervous system.
The blood-brain barrier stops most viruses from entering the brain. So some studies have investigated whether the neurological effects of COVID-19 stem from either a viral invasion of the central nervous system or the systemic effects
of the infection.
One review suggests that both may occur in parallel. In severe infections, oxygen deprivation and a cytokine
storm may damage
the blood-brain barrier and allow SARS-CoV-2 to enter the brain.
backs this up, suggesting that SARS-CoV-2 may disrupt the blood-brain barrier or infect the peripheral neurons, then enter the
central nervous system. Prof. Harris Gelbard, director of the Center for Neurotherapeutics Discovery at the University of Rochester Medical Center, told Medical News Today:
A recent cerebrospinal fluid study
suggests that patients with COVID-19 infection have blood-cerebrospinal fluid barrier dysfunction, with pathology occurring in endothelial cells that line blood vessels in the blood-brain barrier. While this study did not demonstrate evidence for the presence of SARS-CoV-2 in any of the cerebrospinal fluid samples, all patients in this study had PCR-proven COVID-19.
Evidence is growing that COVID-19 can cause neurological damage. One 2020 review
observed that COVID-19 is also anticipated to take a toll on the nervous system in the long term.
asserts that Respiratory virus neurotropism
and collateral injury due to concurrent inflammatory cascades result in various neurologic pathologies, including Guillain-Barré syndrome, encephalopathy, encephalitis, ischemic stroke, intracerebral hemorrhage, and seizures.
Some research has suggested that SARS-CoV-2 might invade the nervous system in the same way that it invades other cells, via agiotensin-converting enzyme 2 (ACE2) receptors.
However, only certain cells in the nervous system have these receptors. Among them are excitatory and inhibitory neurons and other types of cells, such as astrocytes, oligodendrocytes, and endothelial cells.
One review points out that that ACE2 receptors are expressed in small blood vessels in the brain, which could provide a potential entry route for SARS-CoV-2 into the brain.Prof. Gelbard emphasized that the evidence so far of how SARS-CoV-2 might enter the
central nervous system is not conclusive: The pathologic evidence for direct infection of neural cell types, particularly neurons, remain[s] equivocal at best. Despite survey studies of neuronal expression of ACE2 receptors from brain transcriptome databases,  the correlative neuropathology from postmortem human cases is scant.Whether or not the virus invades the
central nervous system, it is clear that SARS-CoV-2 infection can lead to cognitive dysfunction that may last for months or even years after the acute phase of COVID-19.
Many people who are hospitalized with COVID-19 have inflammatory complications, which can affect the nervous system. One study has reported that these patients experience delirium, reduced consciousness, stroke, and other encephalopathies
following SARS-CoV-2 infection.
In this study, the researchers found that the degree of inflammation was correlated with the severity of COVID-19 symptoms and an increase in pro-inflammatory cytokines.
Prof. Gelbard, who was not involved in this study, explains how experts interpret the findings:
Our collective view of this is that SARS-CoV-2 infection/COVID-19 impacts elderly patients with underlying neurovascular disease, whether it is from cerebrovascular disease, subclinical Alzheimers disease, Parkinsons disease or other neurodegenerative disease, by creating a pro-inflammatory central nervous system milieu that is permissive for cognitive impairment, either manifesting as acute delirium or delirium superimposed on dementia.
have shown that people with dementia have increased morbidity and mortality from COVID-19. Many have comorbidities
associated with poor COVID-19 outcome, such as cardiovascular disease, diabetes, hypertension, and obesity.
Dr. Heather Snyder, Alzheimers Associations vice president of medical and scientific relations, told MNT:
The factors causing or contributing to dementia, including hypertension and diabetes, may be what make individuals with dementia more vulnerable to contracting COVID-19.  Research
published in February 2021 in Alzheimers & Dementia: The Journal of the Alzheimers Association found that risk of contracting COVID-19 was twice as high for people living with dementia than those without it.
People with dementia are more at risk of COVID-19 but might the disease worsen existing dementia or cause the development of dementia?
It may be that for people with dementia, SARS-CoV-2 can more easily enter the brain, as the blood-brain barrier is damaged
. This might explain worsening symptoms reported in people with dementia after COVID-19.
states: There is evidence for a bidirectional relationship between viral infections and dementia: People with dementia have an increased risk for infection, while a poor immune response to infection places individuals at increased risk for dementia.
Another risk of COVID-19, and particularly severe forms of this disease, is thrombosis, a cause of strokes. According to one large study, a stroke can double the risk of developing dementia.
People with severe COVID-19 are more likely to have neurological symptoms of the illness, both during its acute phase and afterwards. And severe COVID-19 is more common
in those who are older or have comorbidities, such as overweight or obesity, diabetes, chronic lung disease, and cancers.
Studies suggest that the best way to avoid neurological effects of COVID-19 is to optimize brain and body health in these ways:
- being physically active
- doing cognitively stimulating activities
- sleeping for 7 to 8 hours every night
- having a balanced diet with all the essential vitamins and minerals
- having regular social interactions.
Drug treatments to combat inflammation are also an option. Prof. Gelbard, who is now working on developing such a treatment, commented, What is sorely needed is an appropriate anti-neuroinflammatory intervention with a brain-penetrant therapy that can mitigate this type of neuroinflammatory response.
And, as several experts have noted, vaccination against COVID-19 is one of the most effective ways of minimizing the risk of both severe COVID and long COVID, a view Dr. Snyder reiterated:
While we work to further understand the lasting impacts of COVID-19 on the brain, the take-home message for protecting your cognition is simple: Dont get COVID-19. The best way to not get COVID-19 is to get vaccinated.
As yet, it is unclear whether COVID-19 may be a risk factor for dementia.
Dr. Snyder told MNT that The ongoing COVID-19 pandemic gives us an unwelcome opportunity to study the impact of viral infection on the brain in the short and long term.
She added: Potential viral contributions to Alzheimers and dementia have been long debated within the research community. However, no research to date has shown definitively that a virus can cause Alzheimers disease. Because COVID-19 is still relatively new, we wont know if infection will have an impact on dementia risk for some time.
Prof. Gelbard concurred: Unfortunately, we believe this is the tip of the iceberg. Not to sound like an alarmist, but we echo the sentiments of public health experts: We may feel like we are done with COVID-19, but the virus is not done with us. We expect the aftershocks of this pandemic to continue amplifying the challenge of dealing with neurodegenerative disease in the elderly and immunocompromised.
If you have had COVID-19, it doesnt mean youre going to get dementia. Were still trying to understand this relationship.
Dr. Heather Snyder
While researchers have yet to arrive at conclusive evidence, it appears that the neurological and psychiatric effects of COVID-19 are likely to be with us for many years to come.
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