This is the abstract of a study that University of Illinois researchers published recently in the journal Travel Policy.
Vehicle travel and obesity rates in the United States have surged in recent decades. This paper contributes to the mounting evidence of a link between them by drawing attention to a very close relationship between trends in miles driven per licensed driver and adult obesity rates six years later. It also presents evidence on why the effect might be expected to be lagged by six years. A simple model is produced, which predicts reductions in obesity rates over the next few years. If these reductions come about, the model will be seen to offer a powerful insight into the relationship between driving and obesity. If the relationship is more than coincidental, it has implications for transport policy and supports the development of a multi-pronged, interdisciplinary approach to tackle increased driving and obesity.
The Economist, in reporting on the study, noted that:
These predictions come with a strong caveat: correlation does not equal causation. And it should be noted that the authors did not control for factors such as diet, income and lifestyle. Additionally, they did not explore the possibility that the larger, and thus more immobile, people become, the more they drive.
Croakey asked Chris Rissel, Professor of Public Health, University of Sydney, for his assessment of the findings.
The real problem is sedentary behaviour
Chris Rissel writes:
The study has noted a near perfect correlation between obesity and miles driven by licensed drivers. They report a six year lag period and, because distances driven in the US have decreased recently, the authors predict a decrease in obesity on the horizon.
The association between driving and obesity is not a new one, with a number of studies from a range of developed countries already having observed this pattern.
Further, similar patterns are evident in developing countries as wealth increases and people buy cars and start driving.
Australian research has also noted that after taking into account physical activity levels and a range of potential confounders, people who drive to work are 13% more likely to be overweight or obese than non drivers.
It is an open question whether obesity rates will decline with distances driven. If some driving is replaced with active travel such as walking and cycling, and other factors stay the same, then it is quite possible that it will. However, if the reduced travel is replaced by telecommuting, or other sedentary behaviour, then the answer is no.
The real culprit in this discussion is not driving per se, it is being sedentary.
Even if you exercise vigorously for an hour a day, but then spend the other 23 hours barely moving, this sedentary behaviour is an independent risk factor for obesity and a host of other chronic diseases.
Occupational sitting is becoming a new area of research, and while it’s too early to call in the OH&S consultants, too much sitting is likely to be recognised as a hazard.
PostScript from Croakey:
The US researchers note that there has been substantial investment in reducing obesity rates by promoting healthy food choices and more physical activity. They add:
While personal choices—such as replacing the choices to drive to nearby locations and using elevators with healthier activities such as walking and cycling, and climbing stairs—certainly play a part, realizing a meaningful impact on both obesity and energy consumption will require a societal shift in how we arrange and operate our lives.
A better strategy to curb both energy consumption and obesity rates may be to carve out a national energy policy, a national transportation strategy, an urban planning strategy, and a national public health obesity strategy using the same stroke of the pen.
Some of the benefits and barriers to such policy integration have already been established (Stead, 2008) but without a multi-pronged, systems- thinking approach, it may be futile to expect any efforts in reducingobesity rates to provide effective and sustainable results.
Finally, although we have not yet established a causal link between automobile travel and obesity, the alignment between our results and those of Chow and Hall (2008) is striking and, if obesity data in the coming years turn out to be in line with our model’s prediction, the case for the existence of such a link will be more compelling.
Cycle helmets: the controversy
Meanwhile, Chris Rissel will discuss the pros and cons of bike helmets for adults at the Public Health Association of Australia’s Sax Oration 2011 on Wednesday evening (June 22).
The ACT Branch of PHAA presents the Sax Oration each year in honour of the late Dr Sidney Sax to promote discussion on issues of importance in public health in Australia.
Dr Ian White, PHAA ACT Branch President, said in a statement: “This year’s Sax Oration topic, ‘Legislation for public health: the good, bad and unexpected consequences of bicycle helmet legislation for cycling safety and promotion’, is particularly relevant given the current dual policy emphasis on promoting physical activity to combat obesity, and promoting cycling as an environmentally-friendly mode of transport.”
• Previous Croakey articles on cycle helmets, including some from Chris Rissel, can be found here.