London School of Hygiene & Tropical Medicine

Leave the car at home for a healthier daily commute say authors of new study
Commuting to work by active (walking or cycling) and public modes of transport is linked to lower body weight and body fat composition compared with those using private transport, suggests a UK study published on http://www.bmj.com/content/349/bmj.g4887  today.

The researchers, from the London School of Hygiene & Tropical Medicine and UCL, point out that the benefits were similar for both active (walking and cycling) and public transport, which may have important implications for transport and health policy.

The health benefits of physical activity are well known, and studies suggests that active commuters are at lower risk of being overweight. However, self-reported measures of weight are prone to bias, especially in adults, and there is a lack of good evidence linking active commuting with objective measures of obesity.

So the team of researchers set out to investigate the relationship between active commuting and two known markers for obesity - body mass index (BMI) and percentage body fat.

They analysed 7,534 BMI measurements and 7,424 percentage body fat measurements from men and women taking part in Understanding Society, the United Kingdom Household Longitudinal Study - a large, nationally representative dataset.

A total of 76% of men and 72% of women commuted to work by private motorised transport, 10% of men and 11% of women reporting using public transport, while 14% of men walked or cycled to work compared with 17% of women. Overall BMI score for men was 28 and 27 for women.

Generally, a BMI of 18.5 to 24.9 indicates optimal weight, a BMI lower than 18.5 suggests the person is underweight, a number above 25 may indicate the person is overweight, and a number above 30 suggests the person is obese.

Compared with using private transport, commuting by public and active modes significantly and independently predicted lower BMI and healthier body composition, for both men and women.

Men who commuted via public or active modes had BMI scores around 1 point lower than those who used private transport, equating to a difference in weight of 3kg (almost half a stone) for the average man.

Women who commuted via public or active transport had BMI scores around 0.7 points lower than their private transport using counterparts, equating to a difference in weight of 2.5kg (5.5lb) for the average woman.

Results for percentage body fat were similar in size and significance. And the associations remained after adjusting for several potentially confounding factors, such as age, presence of a limiting illness or disability, monthly income, social class, level of physical activity in the workplace and diet.

The researchers say these differences are larger than those seen in the majority of individually focused diet and physical activity interventions to prevent overweight and obesity.

They point out that although their study was large, no firm conclusions can be drawn about direct cause and effect. However, they say the use of public transport and walking and cycling in the journey to and from work should be considered as part of strategies to reduce the burden of obesity and related health conditions.

Study author Dr Ellen Flint, Research Fellow in Social Epidemiology at the London School of Hygiene & Tropical Medicine, said: "Given that the majority of commuters in the UK use private transport as their main mode of travel, there are potentially large population-level health gains to be made by shifting to more active modes of commuting."

The authors suggest that further research is required in order to confirm the direction of causality in the association between active commuting and body weight.

Publication:

• Ellen Flint, Steven Cummins, Amanda Sacker, Associations between active commuting, body fat, and body mass index: population based cross sectional study in the United Kingdom, BMJ. DOI: 10.1136/bmj.g4887