About that Swedish commute vs health study

Correlation and causation?

I’ve seen a number of links today to this Swedish study showing people who commute by bike are healthier (mentally and physically) than those who drive or take public transportation.

Relationship between commuting and health outcomes in a cross-sectional population survey in southern Sweden

Erik Hansson, Kristoffer Mattisson, Jonas Bjork, Per-Olof Ostergren and Kristina Jakobsson.

BMC Public Health 2011, 11:834 doi:10.1186/1471-2458-11-834
Published: 31 October 2011


Abstract

Background

The need for a mobile workforce inevitably means that the length of the total work day (working and traveling time) will increase, but the health effects of commuting have been surprisingly little studied apart from perceived stress and the benefits of physically active commuting.
Methods

We used data from two cross-sectional population-based public health surveys performed in 2004 and 2008 in Scania, Sweden (56 % response rate). The final study population was 21,088 persons aged 18-65, working >30 h/week. Duration (one-way) and mode of commuting were reported. The outcomes studied were perceived poor sleep quality, everyday stress, low vitality, mental health, self-reported health, and absence from work due to sickness during the past 12 months. Covariates indicating socioeconomic status and family situation, overtime, job strain and urban/rural residency were included in multivariate analyses. Subjects walking or cycling to work <30 min were used as a reference category.

Results

Monotonous relations were found between duration of public transport commuting and the health outcomes. For the category commuting >60 min odds ratios (ORs) ranged from 1.2 – 1.6 for the different outcomes. For car commuting, the relationships were concave downward or flat, with increasing subjective health complaints up to 30-60 min (ORs ranging from 1.2 – 1.4), and lower ORs in the > 60 min category. A similar concave downward relationship was observed for sickness absence, regardless of mode of transport.

Conclusions

The results of this study are concordant with the few earlier studies in the field, in that associations were found between commutation and negative health outcomes. This further demonstrates the need to consider the negative side-effects of commuting when discussing policies aimed at increasing the mobility of the workforce. Studies identifying population groups with increased susceptibility are warranted.

Researchers in Sweden looked at 21,088 adults who commute by walking, driving or bus / train and work full time jobs in Scania, Sweden. In addition to questions on demographics and commute mode, the researchers asked questions about job stress, sleep time, sleep quality, and exhaustion (which the researchers call “low vitality” in their report). Scania and its principle city, Malmö, are located at the southern tip of Sweden and directly across Øresund (“The Sound”) from Copengagen, Denmark.

The surveys show that cyclists sleep better, have less stress, are healthier, suffer less exhaustion, and use fewer sick days than car drivers. Cyclists generally fare better than transit riders in those categories with a few exceptions: People with short (under 30 minutes) transit rides say they sleep better than cyclists.

The survey shows that overall mental health seems about the same across all modes of transport, with one exception: Transit riders with a longer than one hour commute scored lower on mental health than other categories (and perhaps validating the “creeps and weirdos” stereotyping of bus riders?) Mental health was scored using GHQ-12, a standardized psychometric mental health questionaire. The other surprise: those with long (greather than one hour) car drives scored better than those with intermediate (30 to 60 minute) car commutes.

The response from cycling advocates on Twitter, Facebook and Google Plus has been that this survey shows cycling can lead to improved physical health and mental health.

I’m going to be contrarian and provide another possible explanation: only healthy people ride bicycles to work. Sickly folks with low vitality drive because they simply don’t have the energy to get on a bike and go. Cyclists also must have a better self image in the first place to counter the dominant cultural value which emphasizes car travel over active transportation (even in Scania, Sweden, where 71% of commuters drive to work).

I personally believe cycling makes me fitter, stronger, healther, and more balanced than driving to work does, but I don’t believe we can conclude that from the Swedish study.

You can download the the complete published study here.

Speaking of Sweden: Is today the right time to point out the plague of tatooed Swedish devil girls who pull down the pants of innocent cyclists?

8 Comments

  • October 31, 2011 - 8:30 pm | Permalink

    Sorry but I know too many converts to bicycle commuting that would present themselves as counter-examples to your conclusion. 

    Folks that never rode a bicycle before and took anti-depressants now ride their bicycles, drug-free, to places they could take Caltrain. They say they like how they feel and look after riding the bicycle. They also have limited incomes and feel less stressed knowing it costs them virtually nothing to travel by bicycle. Correlation does not necessarily equal causality but they think it does.

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  • Anonymous
    November 1, 2011 - 3:49 am | Permalink

    Hey, I’d rather read this kind of study than the ones that say smog is going to kill cyclists off if global warming doesn’t do it first!

  • November 1, 2011 - 4:12 am | Permalink

    That bit about the drivers with hour-long drives being happier than those with one under a half hour?  Easy.  The suburbs make anyone want to die.  The long drives are coming in from the countryside.

  • Rob E. Loomis
    November 1, 2011 - 8:19 am | Permalink

    I think the point is that either could be true. The study only makes generalizations about groups of people based on their mode of transport, and does nothing to say that the mode of transportation is the cause of the differences. Your point is well taken, and is very possibly valid, but Richard’s theory is also well reasoned and equally valid. The important issue is that neither theory is addressed by the study. People citing the study as evidence that cycling leads to better health are misunderstanding the study.

  • November 1, 2011 - 9:44 am | Permalink

    Correct, Rob — I conclude nothing, only that there’s at least one other explanation. The study shows there’s a correlation between general health and wellbeing for those with active commutes, but it doesn’t show which came first — the health, or the bike commute.

  • November 1, 2011 - 1:52 pm | Permalink

    http://www.youtube.com/watch?v=TjrBdKXgYFY i'll let legally blonde make my point :) (no dead husbands here)

  • Anonymous
    November 2, 2011 - 9:24 am | Permalink

    Interesting study, and interesting point – from my own experience though, I side with the Swedes. I have a folding bike that I ride to work, or more precisely, part of the way to work. I keep the bike in the trunk of my car, and I usually ride about 5 miles round trip every day. Occasionally, I drive the entire way in to work, and on the days I do this, instead of parking in the communal lot and riding in, I am more tired, more irritable, etc. It might just be me, but cycling definitely makes me feel better.

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