Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK.
Environ Health. 2012 Aug 3;11:52. doi: 10.1186/1476-069X-11-52.
Motorised travel and associated carbon dioxide (CO₂) emissions generate substantial health costs; in the case of motorised travel, this may include contributing to rising obesity levels. Obesity has in turn been hypothesised to increase motorised travel and/or CO₂ emissions, both because heavier people may use motorised travel more and because heavier people may choose larger and less fuel-efficient cars. These hypothesised associations have not been examined empirically, however, nor has previous research examined associations with other health characteristics. Our aim was therefore to examine how and why weight status, health, and physical activity are associated with transport CO₂ emissions.
3463 adults completed questionnaires in the baseline iConnect survey at three study sites in the UK, reporting their health, weight, height and past-week physical activity. Seven-day recall instruments were used to assess travel behaviour and, together with data on car characteristics, were used to estimate CO2 emissions. We used path analysis to examine the extent to which active travel, motorised travel and car engine size explained associations between health characteristics and CO₂ emissions.
CO₂ emissions were higher in overweight or obese participants (multivariable standardized probit coefficients 0.16, 95% CI 0.08 to 0.25 for overweight vs. normal weight; 0.16, 95% CI 0.04 to 0.28 for obese vs. normal weight). Lower active travel and, particularly for obesity, larger car engine size explained 19-31% of this effect, but most of the effect was directly explained by greater distance travelled by motor vehicles. Walking for recreation and leisure-time physical activity were associated with higher motorised travel distance and therefore higher CO₂ emissions, while active travel was associated with lower CO₂ emissions. Poor health and illness were not independently associated with CO₂ emissions.
Establishing the direction of causality between weight status and travel behaviour requires longitudinal data, but the association with engine size suggests that there may be at least some causal effect of obesity on CO₂ emissions. More generally, transport CO₂ emissions are associated in different ways with different health-related characteristics. These include associations between health goods and environmental harms (recreational physical activity and high emissions), indicating that environment-health 'co-benefits' cannot be assumed. Instead, attention should also be paid to identifying and mitigating potential areas of tension, for example by promoting low-carbon recreational physical activity.
机动化出行及其产生的二氧化碳（CO₂）排放会造成大量的健康成本；就机动化出行而言，这可能包括导致肥胖率上升。反过来，肥胖也被假设会增加机动化出行和/或 CO₂排放，一方面是因为体重较重的人可能会更多地使用机动化出行，另一方面是因为体重较重的人可能会选择更大、燃油效率更低的汽车。然而，这些假设的关联尚未经过实证检验，以前的研究也没有检验过与其他健康特征的关联。我们的目的是研究体重状况、健康和身体活动如何以及为何与交通 CO₂排放有关。
3463 名成年人在英国三个研究地点的 iConnect 基线调查中完成了问卷，报告了他们的健康状况、体重、身高和过去一周的身体活动情况。使用七天回顾工具评估出行行为，并结合汽车特征数据，用于估计 CO₂排放。我们使用路径分析来检验积极出行、机动化出行和汽车发动机大小在多大程度上解释了健康特征与 CO₂排放之间的关联。
超重或肥胖参与者的 CO₂排放量较高（多变量标准化概率系数超重与正常体重相比为 0.16，95%CI 0.08 至 0.25；肥胖与正常体重相比为 0.16，95%CI 0.04 至 0.28）。较低的积极出行，特别是对于肥胖，以及更大的汽车发动机尺寸解释了这一效应的 19-31%，但大部分效应是由机动车行驶距离的增加直接解释的。休闲步行和休闲时间体育活动与更高的机动化出行距离和更高的 CO₂排放量有关，而积极出行与更低的 CO₂排放量有关。健康状况不佳和患病与 CO₂排放量没有独立关联。
要确定体重状况与出行行为之间的因果关系，需要进行纵向数据研究，但与发动机尺寸的关联表明，肥胖对 CO₂排放可能至少存在一些因果影响。更一般地说，交通 CO₂排放与不同的健康相关特征以不同的方式相关。这些关联包括健康商品与环境危害之间的关联（休闲体育活动与高排放量），表明不能假设环境-健康“共同效益”。相反，还应注意识别和缓解潜在的紧张领域，例如通过促进低碳休闲体育活动。
