Physically fit young adults have healthier white matter in their brains and better thinking skills than young people who are out of shape, according to a large-scale new study of the links between aerobic fitness and brain health. The findings suggest that even when people are youthful and presumably at the peak of their mental prowess, fitness — or the lack of it — may influence how well their brains and minds work.

We already have plenty of tantalizing evidence that aerobic fitness can beneficently shape our brains and cognition. In animal experiments, mice and rats that run on wheels or treadmills produce far more new neurons in their brains than sedentary animals and perform better on tests of rodent intelligence and memory. Similarly, studies involving people show strong relationships between being physically active or fit and having greater brain volume and stronger thinking abilities than people with low fitness or who rarely exercise.

But most of these past studies focused on middle-aged or older adults, whose brains often are starting to sputter and contract with age. For them, fitness and exercise are believed to help slow any decline, keeping brain tissue and function relatively youthful. Much less has been known about whether fitness likewise might be related to the structure and function of healthy, younger people’s brains.

So, for the new study, which was published last month in Scientific Reports, scientists at the University of Münster in Germany decided to look inside the skulls of a large group of young adults.