The Risk of Rising Dementia Cases Due to COVID-19

The Risk of Rising Dementia Cases Due to COVID-19

Facing the unprecedented COVID-19 pandemic, extensive scientific efforts around the world have been studying the SARS-CoV-2 virus to understand how to manage it and what impact it has on health conditions. From the data gathered so far, the medical world has become increasingly concerned about a syndrome known as "long COVID," in which a significant percentage of COVID survivors continue to experience symptoms over an extended period.

A global summary of studies shows that symptoms persist in approximately 5–24% of confirmed COVID survivors, for at least three to four months after infection.

The risk of long COVID is no longer considered to be directly tied to age or the severity of the initial infection. This means younger people, and those with initially mild COVID, can still experience prolonged symptoms. In some cases, symptoms arise quickly during the initial infection and persist for a long time. In others, the same symptoms re-emerge long after the initial infection has passed.

The most commonly reported long COVID symptoms include extreme fatigue and persistent respiratory complications. However, the symptom that has drawn particular concern from specialist doctors and neuroscience researchers is the emergence of difficulty with planning, concentration, and memory — a condition referred to as brain fog.

The Connection Between COVID-19 and Brain Function

From the history of infectious diseases, conclusions exist linking respiratory viruses, including influenza, to impairments in brain function. In the records of the 1918 Spanish flu pandemic, there were many reports of dementia, cognitive decline, and difficulties with motor function and sleep. Evidence from the 2002 SARS outbreak and the 2012 MERS outbreak suggests that these infections caused approximately 15–20% of recovered patients to experience depression, anxiety, memory difficulties, and fatigue.

There is not yet enough data to conclude that SARS-CoV-2 can cross the blood-brain barrier, which normally protects the brain from pathogenic molecules circulating in the bloodstream. However, there are indications that the virus may be able to "hitch a ride" to the brain via the nerves connecting the nose to the brain. Researchers suspect this because in many infected adults, the virus's genetic material has been found in the nasal area that initiates the sense of smell — coinciding with the loss of smell experienced by COVID patients. These nasal sensory cells are connected to the area of the brain known as the limbic system, which is involved in emotion, learning, and memory.

A study in the United Kingdom analyzed the shape and size of the brain in people who had and had not been exposed to COVID. The data showed that part of the brain's limbic system was smaller in those who had been infected. This could signal future vulnerability to brain disease potentially capable of causing dementia, and may play a role in the emergence of prolonged COVID symptoms.

How COVID-19 Affects the Brain

COVID can also affect the brain indirectly. The virus can damage blood vessels and cause bleeding or blockages that disrupt blood, oxygen, or nutrient supply to the brain, particularly to areas associated with cognitive ability in problem-solving. The virus also activates the body's immune system, and in some people this triggers the production of toxic molecules that can disrupt brain function.

The effects of COVID on the nerves that control gut function have also raised concern, with the emergence of stomach and digestive symptoms related to COVID. Medical research has already established that the digestive system and the composition of gut bacteria influence brain function.

The virus can also threaten the function of the pituitary gland, which serves as the master gland that regulates hormone production in the body. This includes cortisol, the hormone that regulates the body's stress response, which when at too-low levels can cause long-term fatigue — a condition found in patients previously diagnosed with SARS, and also observed in COVID patients where fatigue symptoms continued for up to one year after infection.

Implications for Long-Term Public Health

Given the already significant global impact of brain impairment related to dementia and diseases like Alzheimer's, the potential long-term public health consequences of COVID are substantial. Several major unanswered questions about long COVID still require investigation, including how the disease progresses, what its risk factors are, what its health impacts are, and the best ways to treat it.

Understanding what causes the wide variation in symptoms produced by this virus is critically important for global health. Many contributing factors exist, including the type of virus, the severity of the infection, pre-existing conditions, age and vaccination status, and even the level of physical and psychological support provided from the outset of the illness.

While much about long COVID is still being studied, it remains everyone's responsibility to prevent transmission by getting vaccinated and consistently following health protocols.

References

• Carabotti M, et al. The gut-brain axis. Annals of Gastroenterology. 2015;28(2):203–209.
• Kilpatrick T, Petrou S, Handcock S. How does COVID affect the brain? HelloCare. 2021.
• Moghimi N, et al. The Neurological Manifestations of Post-Acute Sequelae of SARS-CoV-2 Infection. Current Neurology and Neuroscience Reports 21, 44 (2021).
• Pal R. COVID-19, hypothalamo-pituitary-adrenal axis and clinical implications. Endocrine 68, 251–252 (2020).
• Whitaker M, et al. Persistent symptoms following SARS-CoV-2 infection in a random community sample of 508,707 people. Institute of Global Health Innovation. 2021.