Can we slow down brain aging and prevent dementia?

Life takes its toll on our brains. Our brain cells pick up wear and tear over the years, causing our minds to become slower, forgetful and have slower movements.

But it's been unclear whether this deterioration is due to the passage of time or if it's predetermined by genes.

Now, a major suite of scientific reviews published in the journal Neuron has tried to answer those questions by taking stock of current understanding of brain aging, and how the risk of age-related cognitive decline and neurodegenerative diseases like Alzheimer's disease can be reduced.

It found that many physical and biological changes are responsible for brain deterioration, which can affect long-term cognitive decline.

And with 152 million people predicted to live with some form of cognitive decline by 2050, finding solutions to those questions is increasingly important.

What causes the brain to age?

"We're understanding the nuts and bolts of aging. In the last 25 years, the critical drivers have been identified through molecular studies," said Costantino Iadecola, a neurologist at Weill Cornell Medical College, US, who led a review on how the brain's vascular system impacts aging.

According to these reviews, the key causes of brain aging are both physical and biological.

Aging physically changes the brain through volume loss and changes in the shape of structural folds — our brains literally shrink.

Biological factors that contribute to declining cognitive health include DNA damage, what Iadecola called "base-level inflammation" across the brain, and the brain's ability to clear waste.

Another review highlighted how the brain's immune system starts to become less "fit" in old age, leaving the brain's health to deteriorate.

In one review, neuroscientist David Rubinsztein from Cambridge University, UK, showed waste protein clearance to be an important driver of ageing and age-related cognitive decline.

As we age, our brain cells become less efficient at clearing harmful waste proteins, which damage the cells and disrupt brain function.

Tau protein is one such harmful protein linked to several neurodegenerative diseases, including Alzheimer's, dementia and impact-related issues like Chronic traumatic encephalopathy (CTE).

"Build-up of Tau protein causes the neurodegenerative disease Alzheimer's disease, so there are clear links between protein clearance mechanisms and neurodegenerative diseases. But we know less about how they affect normal cognitive decline in aging," Rubinsztein told DW.

Scientists are still pondering basic aging questions

A recent survey found scientists studying aging can't agree on some of the fundamental questions challenging the field: What is aging? What causes it? When does it begin?

"These are the questions people have been asking over the ages. It was even discussed in the bible," Iadecola told DW.

But that's one purpose of the Neuron reviews — to highlight what scientists still don't know.

Rubinsztein said part of the problem confronting the field has been an over-focus on studying overt cognitive decline from pathologies like stroke, Alzheimer's disease, or Parkinson's disease, instead of how healthy brains develop these problems.

"We need to understand what age-related cognitive decline really is in the absence of disease. We don't have answers for what normal cognitive decline is in the absence of dementia," Rubinsztein said.

Will we ever be able to slow brain aging?

Scientists are beginning to gain a handle on how to boost our brain health as we get older.

It has long been known that a suite of lifestyle choices reduces the risk of dementia and age-related cognitive decline, these include:

• Encouraging exercise and healthy diet.
• Reducing people's exposure to air pollution and smoking.
• Making sure people are not socially isolated or lonely.
• Treating vision and hearing loss.

Scientists like Iadecola also argue genes play the main role in setting how our brains age from the moment we're conceived.

"Diet, exercise, eliminating toxins by stopping smoking, has a huge impact on how we age. However, genetics is the fundamental factor which determines how we age," said Iadecola.

"You can make aging worse by taking risks like smoking, but you can only make it a bit better by avoiding those risks."

Essentially, that means that a healthy lifestyle can't change a predisposition for brain aging, but a poor lifestyle could accelerate the aging process.

Iadecola is not enthusiastic scientists will be able to treat aging as a disease or artificially prolong life.

"Aging is part of the human condition and there's a limit to how we age. That limiting factor is our genes. There are too many factors that cause aging to prolong life beyond around 120 years," he said.