These prospective cohort studies, especially extending over a few years, are tough
to evaluate. They always have problems with follow-up and with confounding unmeasured
variables, and this study is no exception. Still, it's a subject worthy of better
A group of Spanish investigators utilized a population-based birth cohort called INMA (Infancia y Medio Ambiente, also known as Environment and Childhood). They looked
at a little more than 1000 children's lifestyle habits, reported by their parents
when they were 4 or 6 years of age, and then measured working memory performance at
7 years of age. They found a small decrement in memory scores in children with lower
extracurricular physical activity, perhaps not enough to be clinically significant.
The study had a few problems that the authors discussed very well. For example, the
study questionnaires differed slightly among the 4 different regions of Spain being
sampled. (Why couldn't they make them all the same?) I was most concerned, however,
by the fact that half of the study population was lost to follow up. That's a big
chunk, enough to alter conclusions. Of course, these prospective cohort studies can
only demonstrate associations, and cannot determine cause and effect.
I don't know that I came away with any new pearls of wisdom from the study, but I
do hope these investigators will continue to look at this cohort as they grow older.