Exercise is great for the brain. For one thing, it improves healthy blood flow, which keeps you sharp.

This is why you might find that you think more clearly when out for a walk.

But studies have found that exercise increases the size of the hippocampus, the brain area involved in verbal memory formation, storage and learning.

In other word, exercise promotes the formation of brain cells – and is therefore protective against neurodegenerative diseases such as dementia and Alzheimer’s, which destroy brain cells.

Which is great. But a lot of people won’t – and sometimes can’t – exercise.

How can we help couch potatoes keep their minds intact?

A new study suggests that a blood transfusion from gym junkies might help – by reducing inflammation and boosting memory and thinking skills.

That’s how it worked in mice

Tony Wyss-Coray is a professor in the department of neurology and neurological sciences, Stanford University School of Medicine.

He’s also the associate director, Centre for Tissue Regeneration, Repair and Restoration, and is lead author of the new study.

In 2014, Dr Wyss-Coray and colleagues revealed that blood from young mice rejuvenated elderly rodents’ brains, sharpening their memory.

Those experiments are widely credited for spawning the so-called ‘Dracula cure’ clinics.

These are where old or chronically unwell people – most of them well-moneyed – pay thousands of dollars to have their mouldering blood replaced with that donated by healthy young people.

The new study

In the new study, the Stanford scientists took blood from young mice that had been running marathons on the exercise wheel.

The runner blood was given to lazy mice whose level of activity was akin to going back and forth from the couch to the fridge.

A control group of slacker mice were given a transfusion of slacker blood.

Blood samples showed that the blood from the marathon mice reduced neuroinflammation in the sedentary mice and improved their cognitive performance, as measured in memory tests.

“The mice getting runner blood were smarter,” said Dr Wyss-Coray in a prepared statement.

It was also found that the couch potato mice, following the transfusions, “had more cells that give rise to new neurons in the hippocampus”.

Protein key to controlling inflammation

The researchers isolated a blood-borne protein, named ‘clusterin’, that appears to play an important role in the anti-neuroinflammatory exercise effect.

Clusterin was found to be “significantly more abundant in the marathoners’ blood than in the couch potatoes’ blood”.

When the protein was removed from the marathoner mice’s plasma, the anti-inflammatory effects were largely negated in the sedentary mice’s brains.

“No other protein the scientists similarly tested had the same effect,” the authors say.

Neuroinflammation, a byproduct of the body trying to protect itself against infection, causes the brain fog that comes with flu and other illnesses.

Further experiments showed that clusterin binds to receptors found on brain endothelial cells, the cells that line the blood vessels of the brain.

These cells are inflamed in the majority of Alzheimer’s patients, said Dr  Wyss-Coray, whose research has shown “that blood endothelial cells are capable of transducing chemical signals from circulating blood, including inflammatory signals, into the brain”.

Separately, the investigators found that at the conclusion of a six-month aerobic exercise program, “20 military veterans with mild cognitive impairment, a precursor to Alzheimer’s disease, had elevated clusterin levels in their blood”.

“We’ve discovered that this exercise effect can be attributed to a large extent to factors in the blood, and we can transfer that effect to a same-aged, non-exercising individual,” Dr Wyss-Coray said.

The researchers suggest their findings could open a pathway to new drug treatments for the inflamed brain.