A new study suggests that girls who start school at earlier ages may be less likely to grow into overweight adolescents.
Researchers Ning Zhang and Qi Zhang based their conclusions on 1997 data from a nationally representative sample of more than 14,000 teenage girls. Because birth-date cutoffs for kindergarten entry vary across the United States, the researchers were able to look at large numbers of students who were essentially the same age—having been born just a few days apart—but were in different grades. They found that, by the time they were 16 or 17, girls who had started school a year later had on average a higher body-mass index and were more likely to be overweight or obese than their same-age peers a grade above them.
Why on earth would that be?
The researchers don’t know for sure. But their report, which is published in the current issue of the Journal of Adolescent Health, offers some possible explanations. One is that the girls with one more year of schooling were more likely to interact with more-mature classmates, thus making them more body-conscious at an earlier age. Another idea is that, because the girls in the older grades are further along in their schooling, they may simply be benefiting from an additional year of health and physical education—perhaps one that includes lessons geared to diet and nutrition.
Regardless of the reason, the authors write “our research suggests that earlier admission to school might have a long-term protective effect in terms of adolescent girls’ obesity risks.”
That may not be an argument, in and of itself, for moving up kindergarten cutoff dates. But it’s something to consider.