ARI SHAPIRO, HOST:
There's a lot of scientific evidence showing that vigorous physical exercise also helps your brain. And now scientists think they know at least one reason why. NPR's Jon Hamilton reports on a discovery that could help explain the connection between a fit body and a sharp mind.
JON HAMILTON, BYLINE: Henriette van Praag of the National Institute on Aging has spent years studying how exercise can help you do things like remember the best route to the supermarket.
HENRIETTE VAN PRAAG: There's extensive evidence, both from human and animal studies, that exercise is good for memory.
HAMILTON: But van Prague and a team of researchers wanted to know more about precisely how physical exertion improves memory. And they had a hunch the answer might be found in the cells of the body that are working hardest during exercise.
VAN PRAAG: So we decided to look at factors that could possibly be secreted from muscle.
HAMILTON: Sure enough, the team found that when muscles get exercise, they release a substance called cathepsin B into the bloodstream. And in mice at least, cathepsin B seems to generate new brain cells and new connections in the hippocampus, a part of the brain that is critical to memory. But they still didn't know whether the substance was associated with memory improvement in people. Emrah Duzel, a team member from the German Center for Neurodegenerative Diseases, says they decided to study 43 individuals who were pretty sedentary.
EMRAH DUZEL: The people were university students. They were couch potatoes. They didn't exercise much, and within four months, we really made them fit.
HAMILTON: The former couch potatoes got tough treadmill workouts several times a week. And just like in mice, their cathepsin levels rose as their fitness improved. The students' memory also improved. They did a better job reproducing a geometric pattern they'd seen several minutes earlier. But Duzel says the clincher was the link between memory improvement and cathepsin levels.
DUZEL: You know, those individuals that showed the largest gains in memory also were those that had the largest increase in cathepsin.
HAMILTON: The new research appears in the journal Cell Metabolism. Henriette van Praag says it's pretty clear cathepsin is just one of several factors that improve brain function in people who start working out.
VAN PRAAG: I don't think we have fully explained, you know, how exercise improves memory. But I think we've made a significant step forward.
HAMILTON: Van Praag also says cathepsin has a dark side. It's been associated with tumors and harmful plaques found in the brains of Alzheimer's patients. So raising levels artificially might not be a good idea. Van Praag says there's no doubt regular exercise can help the brain, though she has trouble fitting it into her schedule.
VAN PRAAG: You know, it takes a lot of time and effort to do all this research, so sometimes the exercise regimen suffers a little bit.
HAMILTON: Still, she tries to keep her cathepsin levels up naturally by jogging when she can. Jon Hamilton, NPR News.
NPR transcripts are created on a rush deadline by Verb8tm, Inc., an NPR contractor, and produced using a proprietary transcription process developed with NPR. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.