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- Alex Hutchinson (@sweatscience)
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To ring in the New Year, some good news for those who have been exercising (and for those who haven’t, some incentive to get started in 2010!). It’s yet another study linking cardiovascular fitness and intelligence — a familiar topic, but with a few interesting wrinkles.
Swedish researchers examined the records of 1.2 million men who enlisted in military service at the age of 18 between 1950 and 1976, including 268,000 pairs of brothers and 1,432 pairs of identical twins (read the abstract from the Proceedings of the National Academy of Sciences here). The researchers were particularly interested in young adults, because it’s a time when your brain changes rapidly. Intelligence was positively correlated with cardiovascular fitness (as measured by stationary biking), but there was no correlation between intelligence and muscular strength.
In addition, cardiovascular fitness at age 18 often predicted socioeconomic status and educational attainment later in life. When the researchers examined the twin data, they found that environment, not genetics, played the biggest role in these associations.
To be more precise, genetics explained less than 15% of the variation, while environmental influences explained more than 80%. So fitness is, to a large degree, within your control.
Could this not also just mean that smart people choose to get fit and choose cardio as their venue for increasing fitness? Why does it say that cardio fitness predicts socioeconomic status and not the other way around? How do they know which is dog and which is tail?
Fair question, John. I think that’s where the identical twins come in handy, since the differences in academic achievement and socioeconomic status that accrue over many years can’t be attributed to fundamental differences in “innate” brain power. Instead, they find that the twins that choose to do more endurance exercise as young adults (during key formative years for their brains) go on to have all this subsequent success. Of course, that doesn’t rule out confounding factors that predispose one twin to be smarter in the first place and then get into endurance exercise. Ultimately, epidemiological studies can only prove correlation, not causation — though they can certainly be suggestive, as in this case.