SWEDEN-US: Fit teenage boys are smarter

Men who are fit as teenagers tend to be smarter and more successful in later life, Swedish and US scientists have found. But more brawn does not equate to more brains.

The research has been billed as the first to demonstrate a clear positive association between adolescent fitness and adult cognitive performance and is based on data for the 1.2 million Swedish men born between 1950 and 1976 who enlisted for mandatory military service at the age of 18.

The researchers at the University of Gothenburg and the University of Southern California found that in every measure of cognitive functioning they considered - from verbal ability to logical performance to geometric perception to mechanical skills - average test scores increased according to aerobic fitness. But scores on intelligence tests did not increase with muscle strength, they found.

Nancy Pedersen of the University of Southern California said the positive association of intelligence scores with cardiovascular fitness but not muscular strength supported the idea that aerobic exercise improved cognition through the circulatory system influencing brain plasticity.

She said the central nervous system displayed considerable plasticity during early adolescence and adulthood.

The results, published in the Proceedings of the National Academy of Sciences, showed the importance of getting healthier between the ages of 15 and 18 while the brain is still changing.

The study found that boys who improved their cardiovascular health between ages 15 to 18 demonstrated significantly greater intelligence scores than those who became less healthy over the same 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.

"Direct causality cannot be established. However, the fact that we demonstrated associations between cognition and cardiovascular fitness but not muscle strength... and the longitudinal prediction by cardiovascular fitness on subsequent academic achievement, speak in favour of a cardiovascular effect on brain function," Pedersen said.

The sample included 260,000 pairs of siblings, 3,000 sets of twins, and more than 1,400 sets of identical twins, and the researchers found that even among identical twin pairs, the link between cardiovascular health and intelligence remained strong.

Pedersen said the results provided scientific support for policies to maintain or increase physical education in schools. "Physical exercise should be an important instrument for public health initiatives to optimise cognitive performance, as well as disease prevention at the society level."