Light Rail and Obesity in one NC City

As we try to figure out how to curb an unhealthy increase in obesity, one of the factors under consideration is the built environment. Those who in live in places where few destinations are within walking/biking distance, public transit is limited, and the environment is unfriendly to pedestrians and cyclists may find it harder to get the recommended amount of physical activity. Studying the built environment's effect on obesity is challenging, though. People who live in pedestrian-friendly areas with good public transit may be more likely to get enough activity and less likely to be obese than their counterparts in car-dependent places, but that doesn't demonstrate causation. What if people who hate physical activity naturally gravitate toward auto-dependent areas, and walkers move to places where it's easy to get around on foot?

This is why I was excited to see a study by researchers from the University of Pennsylvania, Drexel University, and the RAND Corporation that takes advantage of a natural experiment to study causality (via Ryan Avent). It was published in the August 2010 issue of the American Journal of Preventive Medicine, and the full text is available for free online.

The natural experiment took the form of a new light rail transit (LRT) line in Charlotte, NC. Researchers conducted two phone surveys with residents living within a one-mile radius of the new line; participants were first interviewed 8-14 months before the LRT opened, and again 6-8 months after the system became operational. The study ended up with a total of 489 respondents who lived in the area and agreed to be interviewed at both times.

Participants were asked for their height and weight (which was then used to calculate BMI) and whether they met weekly recommended physical activity (RPA) through walking. The American College of Sports Medicine and American Heart Association recommend vigorous activity 3 times a week, â¥20 minutes a time; or walking 5 times a week, â¥30 minutes a time. (The study also covers residents' perceptions of the built environment - the whole thing is worth a read for anyone interested in this topic.)

The authors found that "there is a significant association between LRT use and reductions in BMI over time." The details are as follows:

Specifically, LRT reduced their BMI by an average of 1.18 kg/m2 compared to similarly situated non-LRT users over a 12-18 month follow-up period. For a person who is 5â²5â³, that is equivalent to a relative weight loss of 6.45 lbs. Use of LRT is also associated with a reduced odds of becoming obese (OR=0.19, 95% CI=0.04, 0.92). LRT users were 81% less likely to become obese over time. The odds of increasing one's physical activity through vigorous exercise to meet RPA levels is also associated with LRT use (OR=3.32, 95% CI=0.81, 3.63) but was only significant at the p

There are many reasons to shift more of our transportation from single-occupancy vehicles to public transportation, including reducing pollution and congestion and improving quality of life for those who can't drive (whether due to age, physical limitations, or inability to afford a car). If such a shift can also play a role in reducing obesity, that makes the case for transit even stronger. I hope in the coming years we'll see more new transit lines added, and more researchers taking the opportunity of these natural experiments to study how public transportation affects public health.

Citation: MacDonald JM, Stokes RJ, Cohen DA, Kofner A, Ridgeway GK. The Effect of Light Rail Transit on Body Mass Index and Physical Activity. Am J Prev Med 2010; 39(2):105-112. doi: 10.1016/j.amepre.2010.03.016.

More like this

 Image by Jespahjoy. Just before moving to our new home here on Scienceblogs, I asked our readers for ideas on what types of content they would like to see here on Obesity Panacea.  One topic that came up several times was the issue of injuries.  I'm not sure why we haven't discussed injuries in…
Via Ezra Klein, here's a striking infographic from the Bipartisan Policy Center comparing what makes us healthy to how we as a nation spend our health dollars: Infographic from the Bipartisan Policy Center As it illustrates, behaviors are major contributors to our health status, but a tiny…
Slate has just started a new series by Tom Vanderbilt called "The Crisis in American Walking: How we got off the pedestrian path." Vanderbilt observes that it's odd to see things like "Campaign to Get America Walking" when ambulation is one of the most natural activities for our species. Reliance…
It’s not unusual for studies on community walkability to face the perplexing question of self-selection. In other words, people who already like to walk end up moving to walkable communities and so those communities naturally have higher physical activity rates. In even simpler terms, it’s about…

Why isn't climate being considered in this model? Perhaps Charlotte's climate is rather benign. However, even if Houston or New Orleans were the most pedestrian-friendly city in the world, the vast majority of the population would gravitate to the air-conditioned automobile as the preferred mode of transportation.

Climate will trump the built environment any day.