Just how much owning an automobile affects our physical activity habits — and, thus, our health — has been a bit unclear.
It seems intuitive that the less time we spend in a car, the more time we would spend getting to and from places by walking or even cycling. But not all studies have supported that connection. A couple of years ago, researchers reported, for example, that although automobile use in the United States fell by almost 600 miles per person per year between 2004 and 2014, that drop did not appear to have any impact on our overall activity levels.
That’s why I found a study published recently in the BMJ so interesting. It followed the health of 180 adults in Beijing, China, who entered and won a randomized lottery that permitted them to purchase a vehicle permit (license plate) for an automobile. (Since January 2011, to reduce congestion, Beijing has capped the number of new vehicle permits at 240,000 per year.)
The study found that getting a car had a significant impact on people’s physical activity. They walked less. They cycled less. They used less public transit.
And one group of lottery winners — those over the age of 50 — also gained a considerable amount of weight.
These results offer a message for all us. They suggest that the ways we — as individuals and as a society — choose to transport ourselves, particularly in our cities, can have a direct impact on our health.
It’s the randomization of the Beijing lottery that made the study’s authors recognize a rare research opportunity. “We know that the winners should be comparable to the losers on all attributes other than car ownership,” explains Michael Anderson, the study’s lead author and an economist at the University of California, Berkeley, in a released statement.
To find their winners and losers, Anderson and his co-authors used data collected from a sampling of adults who participated in a survey by the Beijing Transportation Research Centre in 2014 and 2016. The survey asked the survey-takers about their use of various methods of transport, as well as whether they had entered the vehicle permit lottery.
Of the 937 people in the sampling, 180 had won a permit to purchase an automobile. Almost all — 91 percent — of the lottery winners did go ahead and get a vehicle.
Anderson and his co-authors then compared the transport habits of the lottery winners with the non-winners. They found that five years after getting their automobile permit, the lottery winners took an average of three fewer rides on public transit per week than their non-lottery-winning peers.
They also walked and cycled an average of 24 fewer minutes per day.
For people under age 50, no significant weight gain was associated with owning a car. But for those over that age, the weight gain was considerable: an average of 23 pounds.
Weight gain is, of course, associated with aging, but eliminating activity may have a particularly large impact on older adults, Anderson points out.
Limitations and implications
The study comes with several caveats. For example, the survey on which the study relied did not include information about the participants’ leisure activity beyond walking and bicycling. “If some individuals responded to a reduction in active transport by exercising at the gym, for example, the total effect of physical activity on weight could be smaller than we estimated,” Anderson and his co-authors acknowledge.
Also, the study included only individuals who were interested in buying a car, so the participants were not randomized from the entire Beijing population.
Still, as the researchers point out, “this population of over one million individuals in a major city with good alternative public transportation is nevertheless of interest because it comprises those likely to become car owners in the near future.”
China’s obesity rate is estimated to be at around 14 percent, well below that of the United States, where it’s now almost 40 percent. But China’s rate has been rising quickly in recent years, especially in cities.
Restricting driving may help contain that rise, this new study suggests. And it might help reverse the obesity epidemic elsewhere.
“Few cities have automobile permit lotteries, but many directly or indirectly restrict vehicle ownership or use,” Anderson and his colleagues write. “Our results suggest that these restrictions could confer considerable public health benefits.”
“The public-health impacts of automobile travel are really important,” Anderson adds. “While cars have saved trillions of hours of travel time globally, they’ve also likely shortened lifespans by trillions of hours in aggregate via traffic accidents, pollution, and obesity-related disease.”
FMI: The study can be read on the BMJ website.