Viral infections including COVID are among the leading causes of dementia – all the more reason to consider vaccination

With more of us living to old age than ever before, dementia is on the rise worldwide, with significant individual, family, social and economic consequences.

Treatment remains largely ineffective and aspects of the underlying pathophysiology remain unclear. But there is good evidence that neurodegenerative diseases – and their manifestation as dementia – are not an inevitable consequence of aging.

Many causes of dementia, including viral infections, are preventable.

COVID and other viral infections are central to brain damage and subsequent neurodegeneration. COVID-positive outpatients are more than three times more likely to develop Alzheimer’s and more than two times more likely to have Parkinson’s.

A study of nearly three million identified risks for psychiatric disorders after COVID infection returned to baseline after one to two months. But other disorders, including “brain fog” and dementia, were still higher than controls two years later.

Among more than six million adults over the age of 65, those with COVID had a 70% greater risk of a new diagnosis of Alzheimer’s disease within a year of testing positive for COVID than those who did not.

More than 150,000 people with COVID and 11 million controls were involved in a study of the long-term effects of acute COVID infection. One year after infection, there was an overall 40% higher risk (an additional 71 cases per 1000 people) of neurological disorders, including memory impairment (80% higher risk) and Alzheimer’s disease (2-fold higher risk). These risks were increased even in people who were not hospitalized for acute COVID.

Read more: These 12 things can lower your risk of dementia – but many Australians don’t know them all

SARS-CoV-2, the virus that causes COVID, can invade brain tissue. Other viruses can also damage the brain directly. A study of nearly two million people showed that those who had been vaccinated against influenza had a significantly lower risk of Alzheimer’s.

The Cost of Dementia

Dementia is characterized by progressive deterioration in cognitive function. This affects memory, thinking, orientation, comprehension, language and judgement, often accompanied by mood swings and emotional control.

It is one of the main causes of disability in older people. The worldwide prevalence exceeds 55 million and there are nearly ten million new cases annually. It is the seventh leading cause of death. In 2019, the estimated global cost of dementia was US$1.3 trillion and counting.

The most well-known form of dementia – Alzheimer’s – was first described in 1907. In general, dementia is described in three stages:

  • Impaired memory, loss of time and getting lost in familiar places

  • further deterioration in memory with forgetting of names and recent events, confusion at home, loss of communication skills and personal care habits, repeated questioning, wandering

  • increasing difficulty walking, progression to inactivity, marked memory loss including failure to recognize relatives and friends, disorientation in time and place, behavioral changes including lack of personal care and emergence of aggression.

Read more: Omicron-specific vaccines may offer slightly better COVID protection – but an immediate booster is your best bet

Treatments largely unsuccessful

There are no cures and no resounding treatment successes. Management includes assisting patients and caregivers in optimizing physical activity, stimulating memory, and treating concomitant physical or mental illnesses.

Dementia has a disproportionate impact on women, who are responsible for 65% of deaths from dementia and provide 70% of the hours of care.

We may know less about the pathology of dementia than we thought: some key data are being scrutinized for possible inappropriate manipulation.

Read more: Alzheimer’s theory undermined by allegations of data manipulation – but does not bring dementia research to its knees

But we know about many causes of dementia and therefore about prevention. In addition to viral infections, there are at least four other causes: cardiovascular disease, type 2 diabetes (especially untreated), traumatic brain injury and alcohol.

The brain has its own immune system – cells called microglia. These play a role in brain development, accounting for 5-10% of brain mass, and are activated by damage and loss of function. They are also implicated in Alzheimer’s and their inflammation has been shown to be central to their pathology.

Dementia is preventable

In the absence of effective treatment, prevention is an important goal. The connection with viral infections means that we should pay close attention to the availability and uptake of vaccines (for influenza, COVID and all future variants) and give greater importance to combating vaccine misinformation.

The association with atherosclerosis and stroke, as well as diabetes, supports primary prevention, which includes a healthier diet (plant-based diet low in salt and saturated fat), physical activity, and weight control.

Alcohol consumption is a major problem worldwide. We have allowed high consumption to become normalized and speak of no more than two glasses a day as if that were harmless. Despite the myth of some positive aspects of alcohol, the safest intake is zero drinks per week.

This requires a complete national rethink of alcohol availability and acceptance, as well as alcohol dependency care and alcohol-related disorder treatment.

Traumatic brain injury is associated with sports and especially with falls and car accidents. Recognized as a global priority, awareness of fall avoidability among older people is growing. The treatment of head injuries is being intensified in contact sports.

However, data on the impact of best management of the initial injury on subsequent risk of dementia are lacking, and the risk remains elevated 30 years after the initial trauma.

Evidence that dementia has preventable causes, including viral infection, should better inform policy and our own behavior.

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