Background Few studies have examined the causal relationship between transport mode and body mass index (BMI).
Methods We examined between-person differences and within-person changes in BMI by transport mode over four time points between 2007 and 2013. Data were from the How Areas in Brisbane Influence HealTh and AcTivity project, a population-representative study of persons aged 40–65 in 2007 (baseline) residing in 200 neighbourhoods in Brisbane, Australia. The analytic sample comprised 9931 respondents who reported on their main transport for all travel purposes (work-related and non-work-related). Transport mode was measured as private motor vehicle (PMV), public transport, walking and cycling. Self-reported height and weight were used to derive BMI. Sex-specific analyses were conducted using multilevel hybrid regression before and after adjustment for time-varying and time-invariant confounders.
Results Independent of transport mode and after adjustment for confounders, average BMI increased significantly and linearly across the four time points for both men and women. Men and women who walked or cycled had a significantly lower BMI than their counterparts who used a PMV. BMI was nearly always lower during the time men and women walked or cycled than when they used a PMV; however, few statistically significant differences were observed. For women, BMI was significantly higher during the time they used public transport than when using a PMV.
Conclusion The findings suggest a causal association between transport mode and BMI and support calls from health authorities to promote walking and cycling for transport as a way of incorporating physical activity into everyday life to reduce the risk of chronic disease.
- longitudinal studies
- physical activity
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Contributors GT conceived the study, undertook the analyses and drafted the manuscript. BAH contributed to the study’s analyses, drafting the manuscript and the interpretation of results. LB provided statistical and methodological advice and contributed to drafting the manuscript. JNR contributed to the interpretation of the data and findings, and drafting and revising the article. WJB and BG-C each contributed to the conception of the article, the interpretation of results, and drafting and revising the article. All authors revised the article for important intellectual content, and each approved the final manuscript as submitted.
Funding This work was supported by the Australian National Health and Medical Research Council (grants APP1047453, APP497236 and APP339718).
Competing interests BG-C is supported by an NHMRC Senior Principal Research Fellowship (APP1107672). JNR is supported by an NHMRC Centre of Research Excellence in Healthy, Liveable Communities (APP1061404) on which GT and BG-C are chief investigators.
Ethics approval The HABITAT study received ethical clearance from the Queensland University of Technology Human Research Ethics Committee (Ref. 3967H and 1300000161).
Provenance and peer review Not commissioned; externally peer reviewed.