External stimulus: Can an athlete’s blood enhance brainpower?

That’s the tantalising prospect raised by a new study in which researchers injected sedentary mice with blood from mice that ran for miles on exercise wheels, and found that the sedentary mice did better on tests of learning and memory.

The study also found that the type of brain inflammation involved in Alzheimer’s and other neurological disorders was reduced in sedentary mice after they received their athletic counterparts’ blood. Scientific results with mice don’t necessarily translate to humans. 

Still, experts said the study supports a growing body of research. “We’re seeing an increasing number of studies where proteins from outside the brain that is made when you exercise get into the brain and are helpful for improving brain health, or even improving cognition and disease,” said Rudolph Tanzi, a professor of neurology at Massachusetts General Hospital and Harvard Medical School. He led a 2018 study that found that exercise helped the brains of mice engineered to have a version of Alzheimer’s.

The most promising outcome would be if exercise-generated proteins can become the basis for treatments, experts said. “The demonstration that there are transferable factors in the blood that seemed to convey beneficial effects on the brain that improve learning and memory is by far the most interesting aspect of the work,” said Dr Madhav Thambisetty, a neurologist and senior investigator at the National Institute on Aging, who was not involved in the new research.

The study, led by researchers at Stanford School of Medicine, found that one protein — clusterin, produced in the liver and in heart muscle cells — seemed to account for most of the anti-inflammatory effects. 

But several experts noted that recent studies have found benefits from other proteins. 

They also said more needs to be learned about clusterin, which plays a role in many diseases, including cancer and may have negative effects in the early stages of Alzheimer’s before brain inflammation becomes dominant.

“It’s far too premature to conclude that higher or lower levels of clusterin might be either beneficial or not,” said Dr Thambisetty, who has studied clusterin. “I don’t think we’re at the stage yet where people can trade in their treadmills or cancel their gym memberships for a clusterin pill or a clusterin injection.”

The study was led by Tony Wyss-Coray, a professor of neurology and neurological sciences at Stanford, who had previously done research finding that the blood of young mice can reverse age-related cognitive impairment in old mice. Dr Wyss-Coray said he wanted to see “if exercise produced factors that would also accumulate in the blood and that you could then transfer them.”

The team also found that the brains of mice with runner blood produced more of several types of brain cells, including those that generate new neurons in the hippocampus, a region involved in memory and spatial learning. 

A genetic analysis showed that about 1,950 genes had changed in response to the infusion of runner blood, becoming either more or less activated. 

Most of the 250 genes with the greatest activation changes were involved in inflammation and their changes suggested that brain inflammation was reduced.