Articles
Active commuting and obesity in mid-life: cross-sectional, observational evidence from UK Biobank

https://doi.org/10.1016/S2213-8587(16)00053-XGet rights and content

Summary

Background

Physical inactivity is a leading cause of obesity and premature mortality. We aimed to examine the relation between active commuting and obesity in mid-life using objectively measured anthropometric data from UK Biobank.

Methods

Cross-sectional, observational data from UK Biobank were used. These were collected from individuals aged 40-69 years who visited 22 assessment centres across the UK between 2006 and 2010. Self-reported commuting method was operationalised into seven categories, ordered to reflect typical levels of physical exertion. The outcomes assessed were BMI (based on objectively measured weight and height) and percentage body fat. Hypothesised confounders were income, area deprivation, urban or rural residence, education, alcohol intake, smoking, leisure physical activity, recreational walking, occupational physical activity, general health, and limiting illness or disability. We used sex-stratified multivariate linear-regression models.

Findings

Final complete case sample sizes were 72 999 men and 83 667 women for the BMI outcome and 72 139 men and 82 788 women for the percentage body fat outcome. Active commuting was significantly and independently associated with reduced BMI and percentage body fat for both sexes, with a graded pattern apparent across the seven commuting categories. In fully adjusted models, compared with their car-only counterparts, mixed public and active transport commuters had significantly lower BMI (men: β coefficient −1·00 kg/m2 [95% CI −1·14 to −0·87], p<0·0001; women: −0·67 kg/m2 [–0·86 to −0·47], p<0·0001), as did cycling or cycling and walking commuters (men: −1·71 kg/m2 [95% CI −1·86 to −1·56], p<0·0001; women: −1·65 kg/m2 [–1·92 to −1·38], p<0·0001). Similarly, compared with car-only commuters, mixed public transport and active commuters had significantly lower percentage body fat (men: −1·32% [95% CI −1·53 to −1·12], p<0·0001; women: −1·10% [–1·40 to −0·81], p<0·0001), as did cycling or cycling and walking commuters (men: −2·75% [95% CI −3·03 to −2·48], p<0·0001; women: −3·26% [–3·80 to −2·71], p<0·0001).

Interpretation

This study is the first to use UK Biobank data to address the topic of active commuting and obesity and shows robust, independent associations between active commuting and healthier bodyweight and composition. These findings support the case for interventions to promote active travel as a population-level policy response for prevention of obesity in mid-life.

Funding

UK Medical Research Council.

Introduction

Physical inactivity is one of the leading causes of morbidity and premature mortality.1, 2 In England, two-thirds of adults do not meet recommended levels of physical activity.3 The mass adoption of private motorised transport has contributed to declines in active travel worldwide. In England and Wales, 23·7 million individuals regularly commute to a workplace, 67% by car.4 Individuals who commute to work actively achieve higher levels of total physical activity than do car users, independent of leisure physical activity.5, 6, 7, 8 Active commuting has been identified by the UK National Institute for Health and Clinical Excellence (now National Institute of Health and Care Excellence) as a feasible way to increase population physical activity without requiring unacceptable financial or time expenditure.9

Middle age is an important life-stage for the development of obesity. In the 2012 Health Survey for England, BMI was found to increase steadily into middle age, before declining beyond age 75 years.10 In the same survey, 44% of adults aged 55–64 years did not meet recommended physical activity levels.11 Using survey data from the UK Household Longitudinal Study, Laverty and colleagues12 reported that after adjustment for socioeconomic and demographic factors, compared with 16–29 year olds, adults aged 50–65 years were 55% less likely to commute by public transport, 45% less likely to commute on foot, and 30% less likely to commute by bicycle.

Previous research has shown that, compared with car commuters, walkers and cyclists have lower BMI,12, 13, 14, 15 lower percentage body fat,13 and lower waist circumference.15 Walkers and cyclists are less likely to report diagnoses of diabetes and hypertension,13, 14, 15 and report higher levels of physical wellbeing than do car commuters.16 Compared with continued car use, switching from sedentary to active commuting was found to predict a decrease in self-reported BMI.17 However, many individuals live too far from their workplace for walking or cycling to be feasible. Cross-sectional studies have shown that individuals who commute by public transport have significantly lower BMI, percentage body fat, and self-reported diagnoses with diabetes and hypertension, and that associations are similar in size to those seen for walking and cycling.12, 13 This finding suggests that incidental physical activity involved in public transport journeys has an important role. Increasing evidence consistently suggests that mass transit contributes to overall physical activity18, 19 and is negatively associated with obesity. 20, 21

Research in context

Evidence before this study

Previous studies have found evidence of an association between active commuting and a range of obesity-related and cardiovascular disease-related health outcomes in the UK. Walking, cycling, and taking public transport to work have been shown to predict self-reported and objectively measured BMI, objectively measured percentage body fat, self-reported doctor-diagnosed diabetes, and self-reported hypertension. However, previous studies have been hampered by insufficiently detailed information about method of commuting exposures (making it largely impossible to capture mixed-mode journeys, for example), self-reported outcome measures, limited scope to control for confounding by health behaviours especially diet, and small sample sizes for meaningful subgroup analyses.

Added value of this study

This study is the first to use UK Biobank data to investigate the relation between commuting behaviour and BMI, based on objectively measured bodyweight and height; and body fat. UK Biobank is a large, observational study of middle-aged individuals in the UK. This dataset offers the opportunity to do a definitive cross-sectional, observational investigation into the relation between active commuting and obesity in terms of sample size, gradation of exposure, robust biological measures, and use of a wide range of covariates. The age span of the participants covers a key life-stage for the development of physical inactivity, obesity, and related cardiovascular risk. UK Biobank allows a substantially more detailed and fine-grained categorisation of method of commute exposure by allowing the derivation of mixed-mode categories. This study also uses objectively measured height, bodyweight, and percentage body fat, so is not subject to bias introduced when respondents are asked to report their own measurements. The comprehensive range of socioeconomic, demographic, behavioural, occupational, and health data available in UK Biobank allowed us to do comprehensive adjustment for confounding. Additionally, we were able to further isolate independent associations between active commuting and obesity in sensitivity analyses controlling for dietary energy intake. To our knowledge, this is the first study of active commuting and obesity to incorporate this dimension.

Implications of all the available evidence

The results of this study add to the growing evidence suggesting that the promotion and facilitation of active commuting should form part of the policy response for population-level obesity prevention.

However, important gaps in the scientific literature remain. First, it is unclear whether active commuting has a graded relationship with obesity. Operationalising the exposure using multiple mixed-mode categories provides better observational evidence of causality, but existing studies are hampered by inadequately detailed measurement. Second, the use of objectively measured obesity is important to reduce the bias associated with self-reporting. A third common limitation of the use of secondary datasets to investigate active commuting and bodyweight is the failure to rule out confounding by energy intake. The extent to which associations between active commuting and obesity are moderated by demographic and socioeconomic factors is also underexplored in the existing scientific literature.

This study is the first to use data from UK Biobank22, 23 to investigate the relation between active commuting and obesity. A large and comprehensive dataset, UK Biobank offers the opportunity to address key limitations in the existing literature. The aim of this study is to investigate the relation between active commuting and objectively measured indicators of obesity in a middle-aged UK population sample. Our hypotheses are that an independent association exists between commuting mode and two measures of obesity (BMI and percentage body fat); adjustment for socioeconomic, demographic, health, and occupational and leisure factors will not fully attenuate the central association; dietary energy intake will have a small but significant confounding effect; among walkers and cyclists, distance of commute will be independently, inversely associated with BMI and percentage body fat.

Section snippets

Study design and data collection

We used baseline data from UK Biobank (project 5935) to do a cross-sectional, observational study to assess the relation between commuting method and mid-life obesity. Data were collected from 502 656 individuals aged 40–69 years who visited 22 assessment centres across the UK between 2006 and 2010. Respondents were selected through National Health Service (NHS) patient registers based on distance from their nearest UK Biobank assessment centre. The scientific rationale, study design, ethical

Results

The most prevalent method of commuting was car travel (64% of men and 61% of women; table 1). 4% of men and 7% of women reported walking as their only method of commute, and a further 4% of men and 2% of women reported cycling only or a mix of cycling and walking. Overall, 23% of men and 24% of women used active transport either solely or as a component within a mix of methods. The percentage body fat analytical sample was representative of the BMI analytical sample on key variables. A

Discussion

Our results show a significant, independent association between method of commuting and both BMI and percentage body fat for men and women. Comprehensive adjustment for confounders only slightly attenuated the observed central associations. The largest associations were seen for cyclists versus car users. For example, male cyclists had a BMI on average 1·71 kg/m2 lower than their car-using counterparts after adjustment for socioeconomic, demographic, health, and behavioural factors, and other

References (29)

  • Statistics on obesity, physical activity and diet: England 2015

    (2015)
  • A Goodman

    Walking, cycling and driving to work in the English and Welsh 2011 census: trends, socio-economic patterning and relevance to travel behaviour in general

    PLoS One

    (2013)
  • S Audrey et al.

    The contribution of walking to work to adult physical activity levels: a cross sectional study

    Int J Behav Nutr Phys Act

    (2014)
  • Walking and cycling: local measures to promote walking and cycling as forms of travel or recreation. NICE public health guideline PH41

  • Cited by (115)

    View all citing articles on Scopus
    View full text