Being physically fit at age 18 is linked to a higher IQ, a new study finds.
The researchers also showed that fitness predicts greater educational and professional achievements later in life.
Earlier studies have found links between physical fitness and mental functioning in animals, children and older adults. But the relationship in young adults hasn’t been clear.
In the new study, researchers drew on large datasets to examine over 1.2 million young men born in Sweden between 1950 and 1976. All the men had their physical fitness and intelligence assessed at age 18 when they enlisted for military service. The researchers—based primarily at the University of Gothenburg and the Karolinska Institute in Sweden—compared this information to details of later academic achievement and socioeconomic status from other national databases. The findings appeared in the December 8, 2009, edition of the Proceedings of the National Academy of Sciences.
Cardiovascular fitness in the 18-year-olds, as measured by stationary cycling, was strongly linked to scores on intelligence tests. The association remained even after adjusting for confounding factors. Muscular strength, in contrast, showed little relationship to intelligence.
“Being fit means that you also have good heart and lung capacity and that your brain gets plenty of oxygen,” says study coauthor Dr. Michael Nilsson of the University of Gothenburg. “This may be one of the reasons why we can see a clear link with fitness, but not with muscular strength.”
To learn more about the influence of family and genetics, the researchers analyzed a subset of about 270,000 men who had siblings in the study, including about 1,500 genetically identical and 2,000 non-identical twins. Twin information was culled from the Swedish Twin Registry, supported in part by the Swedish Research Council and NIH.
If the link between fitness and intelligence were entirely due to genes and upbringing, the researchers note, they wouldn’t find an association among pairs of identical twins. However, the correspondence between cardiovascular fitness and intelligence scores remained strong. Thus the link between fitness and intelligence appears to arise mainly from environmental factors.
The researchers also found that fit teens were more likely to obtain a university degree later in life. Fitness at age 18 was likewise linked to landing better jobs, with higher pay or management responsibilities, up to 36 years later.
The findings point to the importance of encouraging physical fitness in teens. “This being the case, physical education is a subject that has an important place in schools,” says study lead author Dr. Maria Åberg of the University of Gothenburg.
—by Vicki Contie