A new study proves the old Roman saying, "A sound mind in a sound body" — the more fit one's heart is, the more one's brain seems to benefit, scientists now find.
Many earlier studies have linked physical exercise with brainpower in humans and animals, but most of the research in people focused on children or older adults. The few studies of young adulthood — when the brain changes rapidly, establishing many traits linked with intelligence — have yielded ambiguous data.
To help resolve this conflict, in a massive study, researchers investigated nearly all Swedish men born between 1950 and 1976 who were conscripted at age 18 into military service, which is compulsory in Sweden. The sample of a whopping 1,221,727 men used data on physical fitness and intelligence performance, and included 268,496 full sibling pairs and 3,147 twin pairs, of whom 1,432 were identical.
The scientists discovered that cardiovascular fitness was linked with overall intelligence, although the same did not hold true for muscle strength and brainpower. Cardiovascular fitness was also linked with scores on tests of logical, verbal, technical and visuospatial capabilities and even socioeconomic status and educational attainment later in life.
"The saying, 'mens sana in corpore sanum' — 'a healthy mind lives in a healthy body' — is about 2,000 years old," said researcher Georg Kuhn, a neuroscientist at the University of Gothenburg in Sweden.
Kuhn explained cardiovascular exercise increases blood flow to the brain, supplying it with more oxygen and nutrients. Moreover, during exercise, growth factors are produced that could improve brain structure over time. This not only includes more and stronger connections between nerve cells, but also more neurons and supporting cells. "From animal experiments we know this is the case especially in the hippocampus, a region of the brain that is important for learning and memory," he said.
It is also possible that smarter people exercise more, Kuhn said. However, their twin data suggests not. When the researchers looked at twins, they found that environment, not genetics, played the biggest role in these links. "The fitter twin is also the more intelligent twin," he noted.
Past research has suggested that cardiovascular fitness can benefit the minds of older adults. For instance, it can delay or reduce the onset and progression of dementia and Alzheimer's disease.
"The findings can be used to argue for a more balanced school curriculum," Kuhn said. "It is a better argument for school kids to grasp that they can be more successful in life if they study and exercise, than telling them that, with regular exercise, their chance for Alzheimer's disease after they are 60 years old will decrease by X percent."
The scientists detailed their findings online Nov. 30 in the Proceedings of the National Academy of Sciences.