When I was your age, I walked 5 miles to school every day! Barefoot! Uphill! Both ways! In the snow!! – PhD Students to undergrads

Active transportation, that is, biking, walking, rollerblading or skateboarding to school, has been shown to be associated with health benefits and increased energy expenditure. This varies from country to country however, with some countries having higher rates of active transportation. The Netherlands and Scandinavian countries have been very committed to ensuring that their cities are easy to navigate, and have made biking an integral part of their city planning and infrastructure (an issue discussed by friend of the blog Megan here).

However, it is unknown whether biking to school can affect BMI status. While cross-sectional studies exist, and show that those who cycle are physically fitter than their peers, you cannot conclude anything about causality or temporality from these studies. So Bere et al. investigated the longitudinal associations between biking to school and weight status among youth.

More after the jump.

Rotterdam Football Club. Notice the bike racks out front - a deliberate measure taken to encourage people to bike.

What did they do?

The study used two data sources: for their Dutch sample, they used the ENDORSE study (ENvironmental Determinants of Obesity among Rotterdam SchoolchildEn), while for their Norwegian sample, they used Youth In Balance. Both studies are prospective cohort studies, with the first following youth at 12-13 and then again at 14-15 years of age, while the second follows youth in grades 8, 9 and 10. They measured height and weight of all youth at all time points, and used this for their analyses.

With regards to active commuting, they considered anyone who biked more than three days a week or more an “active commuter.” Since this was a longitudinal study, they then categorized people into one of four groups: 1) never cycled (didn’t bike at either time point), 2) started cycling (biked at time 2, but not time 1), 3) stopped cycling (biked at time 1, but not time 2) and 4) continued cycling (biked at both time points).

What did they find?

Their results were interesting. 467 kids didn’t bike at either time point, 50 started, 97 stopped and 276 continued. So there wasn’t a lot of change between groups.

Among three of the four groups, the prevalence of overweight and obesity didn’t change. However, among those who stopped cycling to school, the prevalence of overweight and obesity increased from 9% to 18%. After adjusting for weight status at baseline, they found that they had a 3.18-fold increase in the odds of being overweight or obese (95% CI: 1.41-7.24).

And what now?

Well, they didn’t find that BMI changed in three of their four groups, but in the group where it did change, they saw strong and significant results. However, since it was observational, you cannot infer that simply stopping biking led to the increased weight gain (a fact the authors readily acknowledge in their discussion). There may have been many other factors at play here.

Future research should look into reasons behind biking to school. In the Scandinavian countries and Holland, there have been deliberate steps taken to ensure people bike, but why did half of the sample still not bike to school? Why do people stop biking? What concerns do they have that prevent them from biking? Some of these concerns may be things we can address, and encourage people to actively commute.

Bere E, Oenema A, Prins RG, Seiler S, & Brug J (2011). Longitudinal associations between cycling to school and weight status. International Journal of Pediatric Obesity, 6 (3-4), 182-7 PMID: 21644849