The results of the study also show the importance of getting healthier between the ages of 15 and 18 while the brain is still changing.
The research team looked at data for all 1.2 million Swedish men born between 1950 and 1976 who enlisted for mandatory military service at the age of 18. In every measure of cognitive functioning they analyzed – from verbal ability to logical performance to geometric perception to mechanical skills – average test scores increased according to aerobic fitness.
Boys who improved their cardiovascular health between ages 15 to 18 exhibited significantly greater intelligence scores than those who became less healthy over the same time period. Over a longer term, boys who were most fit at the age of 18 were more likely to go to college than their less fit counterparts.
Although they could not establish directly causality, the fact that they "demonstrated associations between cognition and cardiovascular fitness but not muscle strength . . . and the longitudinal prediction by cardiovascular fitness on subsequent academic achievement, speak in favor of a cardiovascular effect on brain function," USC researcher Nancy Pedersen said.
In their sample, the researchers also looked at 260,000 full-sibling pairs, 3,000 sets of twins, and more than 1,400 sets of identical twins. Having relatives enabled the research team to evaluate whether the results might reflect shared family environments or genetic influences.
Even among identical twin pairs, the link between cardiovascular health and intelligence remained strong, according to the study. Thus, the results are not a reflection of genetic influences on cardiovascular health and intelligence. Rather, the twin results give further support to the likelihood that there is indeed a causal relationship.
"The results provide scientific support for educational policies to maintain or increase physical education in school curricula," Pedersen said. "Physical exercise should be an important instrument for public health initiatives to optimize cognitive performance, as well as disease prevention at the society level."
Citation: Maria A. I. Åberga, Nancy L. Pedersen, Kjell Toréne, Magnus Svartengrenf, Björn Bäckstrandg, Tommy Johnssonh, Christiana M. Cooper-Kuhna, N. David Åberga,i Michael Nilssona, H. Georg Kuhn, 'Cardiovascular fitness is associated with cognition in young adulthood', PNAS, 2009, doi: 10.1073/pnas.0905307106