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Will biking to work help you “shed the pounds”? BMJ news release nails the big picture but offers nothing more

Strengthens case for incentivising walking or cycling to boost population health, say researchers

Switching from driving to work to using public transport, walking, or cycling might help commuters shed weight within a couple of years, suggests research published online in the Journal of Epidemiology & Community Health.

Given that car use is high, the findings strengthen the case for incentivising walking or cycling to boost population health, suggest the researchers.

They base their findings on the responses of 4000 people to three waves of the British Household Panel Survey (BHPS) in 2004-5, 2005-6, and 2006-7.

The BHPS is a long term annual study of a representative sample of adult Britons which began in 1991-2.

At each time point, respondents described their usual main mode of transport for their daily commute, and provided details of their height and weight (BMI) in 2004-5 and in 2006-7.

The researchers used a series of analyses to see if changes in mode of transport were linked to changes in weight over a two year period.

In the first analysis, which included 3269 respondents, 179 people had stopped driving to work and were either walking or cycling (109) or taking public transport (70).

The ‘switchers’ tended to be younger and less likely to have access to a car than those who continued to drive.

Those who chose to walk or cycle instead tended to have a lower household income and a shorter commute—which became shorter still after making the switch—while those who opted for public transport were significantly more likely to be more highly educated.

Switching from a car  to walking, cycling, or public transport was associated with a statistically significant average reduction in BMI of 0.32 kg/m2 after taking account of other influential factors—equivalent to a difference of around 1 kg a person, on average.

The longer the commute, the stronger was the association, with a reduction in BMI of 0.75 kg/m2 (equivalent to a weight loss of around 2 kg) associated with journeys of more than 10 minutes, and 2.25 kg/m2 associated with journeys of more than 30 minutes—equivalent to weight loss of around 7 kg, on average.

In the second analysis, which included 787 people, 268 switched from active to passive travel. Some 156 stopped walking or cycling and 112 switched from public transport (usually a bus or coach) to the car.

Once again, the ‘switchers’ tended to be younger than those who continued with their mode of transport.

Those who stopped walking or cycling to work were significantly less likely than those who stopped using public transport to be in a managerial or professional post. They also tended, on average, to have a shorter commute, which lengthened after the switch.

Those who had previously used public transport, on the other hand, had a short commute after the switch.

But switching to a car was associated with a significant weight gain of around 1kg per person (or 0.34 kg/m2 ) after taking account of other influential factors.

This is an observational study, so no definitive conclusions can be drawn about cause and effect. Nevertheless, the analysis of individual level changes in BMI over time between the two groups of switchers, using data from a nationally representative survey, strengthens their findings, say the researchers.

If a larger proportion of commuters were able to abandon their cars for a more physically active commute, this could help drive down the average population BMI, they suggest.

“Combined with other potential health, economic, and environmental benefits associated with walking, cycling and public transport, these findings add to the case for interventions to promote the uptake of these more sustainable forms of transport,” they write.

Notes for editors:
Research: Impact of changes in mode of travel to work on changes in body mass index: evidence from the British Household Panel Survey doi 10.1136/jech-2014-205211

Journal: Journal of Epidemiology & Community Health

Author contact:
Mr Adam Martin, Health Economics Group and UKCRC Centre for Diet and Activity Research (CEDAR), Norwich Medical School, University of East Anglia, Norwich, UK via UEA press office
Tel: + 44 (0) 1603 592 352
Email: press@uea.ac.uk

Embargoed link to research: http://press.psprings.co.uk/jech/may/jech205211.pdf
Public link to research: http://jech.bmj.com/lookup/doi/10.1136/jec-2014-205211

About the journal:
The Journal of Epidemiology & Community Health is one of more than 50 specialist journals published by BMJ. The title is the official journal of the Society of Social Medicine. http://jech.bmj.com

Embargoed 23.30 hours (UK time) Thursday night 7 May 2015

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Switching to public transport or cycling/walking to get to work might help shed the pounds: Strengthens case for incentivising walking or cycling to boost population health, say researchers

Our Review Summary

A businessman riding his bicycle to work in the city central while wearing a bicycle helmet

This release reported on a study that tracked changes in participants’ weight as they used different modes of transportation to get to work. The study found that participants tended to lose weight when they switched from taking a car to walking, bicycling, or using public transport (and vice versa). The release did a good job of quantifying the results of the study and explaining the limitations of the research. It could have added more context for readers by mentioning cost differences between commuting methods, potential harms of alternative commuting approaches, funding sources for the study, and any previous research that has addressed this issue.

 

Why This Matters

According to the most recent U.S. census data, the majority of Americans use personal automobiles as their main form of transportation. What are the health impacts of our reliance on automobiles? The research covered in this news release tried to determine if non-automobile commuting methods (walking, bicycling, and public transportation) were associated with changes in one indicator of health — bodyweight — relative to commuting via automobile. As might be expected, they found that participants with self-powered commutes tended to weigh less than when they used a car to get to work. As the researchers point out, “these findings add to the case for interventions to promote the uptake of these more sustainable forms of transport.”

Criteria

Does the news release adequately discuss the costs of the intervention?

Not Satisfactory

The release failed to mention any costs or savings associated with the different commuting approaches discussed in the study. A mention of any of the following costs such as public transportation fees, gasoline/fuel costs, vehicle maintenance, etc., would have earned the release a satisfactory rating.

Does the news release adequately quantify the benefits of the treatment/test/product/procedure?

Satisfactory

This release did an excellent job quantifying the potential benefits of switching to alternative commuting methods. Average reductions or gains of Body Mass Index (BMI) values were clearly stated, in addition to equivalent values in the unit of kilograms (kg) — a nice clarification for many who do not understand what BMI entails.

Does the news release adequately explain/quantify the harms of the intervention?

Not Satisfactory

This release failed to mention any potential harms associated with various types of commutes. It could have earned a Satisfactory rating here by discussing the risk of injuries associated with regular cycling vs. the risk of being injured in a car accident.

Another “harm” the release could have acknowledged is housing affordability and how that affects how close someone is able to live to their place of employment. This release could easily be dismissed by readers who work in areas that are unaffordable to live in and who therefore don’t have the option to walk or cycle to work.

Does the news release seem to grasp the quality of the evidence?

Satisfactory

The quality of evidence presented in this release was Satisfactory, mainly due to the clarity of its presentation. All of the presented evidence appropriately used the word “associated” to imply a correlation rather than a causation. Reduction in BMI was “associated” with a switch to non-driving commuting, not “caused by.” Furthermore, the story explains the limitations of their chosen observational study design by stating, “…no definitive conclusions can be drawn about cause and effect.” In addition, the release alludes to the study researchers controlling for confounding in their analysis.

Does the news release commit disease-mongering?

Satisfactory

This was an especially refreshing “Satisfactory” mark for this release. It would have been extremely tempting to exaggerate automobile-based commuting as a serious health detriment. However, this story clearly presents the weight-loss benefits associated with alternative commute methods, without putting undue emphasis on the potential health issues associated with having a higher weight.

Does the news release identify funding sources & disclose conflicts of interest?

Not Satisfactory

The study was funded mainly by public health agencies in the UK, which adds to the credibility of the research. However, the release does not mention who funded the study.

Does the news release compare the new approach with existing alternatives?

Not Satisfactory

When considering that the benefit posited by this study was weight loss, this release did not present alternatives to a satisfactory level. It would have been nice to at least see a mention of other weight-loss methods. For example, does switching to a healthier diet also have the same impact on BMI as the effect of switching commute?

Does the news release establish the availability of the treatment/test/product/procedure?

Not Satisfactory

Although the availability of non-automobile commute methods is arguably obvious, the release failed to at least mention the potential barriers that individuals may face when trying to use alternative methods. Switching to a different commuting method may be more difficult for certain individuals due to a variety factors — i.e. lack of suitable public transportation or bicycle-friendly road systems. It would have been better if the story at least acknowledged these difficulties.

Does the news release establish the true novelty of the approach?

Not Satisfactory

Although physical activity is not a novel approach to lowering BMI, it would have been nice to understand how the results found by these researchers add to a research gap or other information not already known about physical activity and BMI.

Does the news release include unjustifiable, sensational language, including in the quotes of researchers?

Satisfactory

This release did not use any unjustifiable language when presenting the evidence. It would have been very easy for this release to exaggerate the study’s claims. However, that temptation was successfully avoided.

Total Score: 4 of 10 Satisfactory

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