Walking to a pathway for cardiovascular effects of air pollution
Authors: George D Thurston, Jonathan D Newman
Journal: The Lancet (2017)

There is a well documented association between human exposure to fine particulate matter air pollution (PM2.5) and an increased risk of cardiovascular disease and death.1Brook RD Rajagopalan S Pope 3rd, CA et al.Particulate matter air pollution and cardiovascular disease: an update to the scientific statement from the American Heart Association.Circulation. 2010; 121: 2331-2378Crossref PubMed Scopus (4486) Google Scholar, 2Xie W Li G Zhao D et al.Relationship between fine particulate air pollution and ischaemic heart disease morbidity and mortality.Heart. 2015; 101: 257-263Crossref PubMed Scopus (177) Google Scholar Indeed, the Global Burden of Disease (GBD) study3Cohen AJ Brauer M Burnett R et al.Estimates and 25-year trends of the global burden of disease attributable to ambient air pollution: an analysis of data from the Global Burden of Diseases Study 2015.Lancet. 2017; 389: 1907-1918Summary Full Text Full Text PDF PubMed Scopus (3224) Google Scholar recently estimated that exposure to PM2·5 contributed to 4·2 million deaths in 2015, representing the fifth-ranked risk factor for global deaths; of these, mortality from cardiovascular disease (CVD; ie, ischaemic heart disease and cerebrovascular disease) accounted for most deaths attributed to ambient PM2·5 air pollution. However, despite these strong epidemiological associations and the documented widespread adverse health effects, the exact biological mechanisms and the types of particles that are most responsible for the PM2.5–CVD associations are not well defined. In The Lancet, Rudy Sinharay and colleagues4Sinharay R Gong J Barratt B et al.Respiratory and cardiovascular responses to walking down a traffic-polluted road compared with walking in a traffic-free area in participants older than 60 years with chronic lung or heart disease and age-matched healthy controls: a randomised, crossover study.Lancet. 2017; (published online Dec 5.)http://dx.doi.org/10.1016/S0140-6736(17)32643-0PubMed Google Scholar use a simple but elegant randomised crossover design to gain insight into the type of pollution that can lead to the air pollution–CVD associations that have been reported in population-based epidemiological studies, as well as to identify specific cardiovascular changes consistent with the causality of those associations. The researchers studied the effects of traffic pollution exposure in adult participants aged 60 years and older during a 2 h walk along a busy commercial street in London, England (Oxford Street) compared with a similar walk in a nearby London park (Hyde Park), which has much lower air pollution. 40 healthy volunteers, 40 participants with chronic obstructive pulmonary disease, and 39 participants with ischaemic heart disease took part. In all 119 participants, irrespective of disease status, walking in Hyde Park led to an increase in lung function and a decrease in arterial stiffness, measured as pulse wave velocity and augmentation index, following the walk. By contrast, these beneficial responses were significantly diminished after walking along the more polluted Oxford Street. Specifically, among healthy volunteers the investigators reported a roughly 5% (95% CI −10·40 to −0·27) decrease in pulse wave velocity from 2 to 26 h after the Hyde Park walk, an exercise benefit that was not only negated but even reversed 26 h after the Oxford Street walk (7% increase in pulse wave velocity, 95% CI 2·16 to 12·20). Thus, the multifactorial benefits of low-to-moderate intensity physical activity, such as walking, for the primary and secondary prevention of CVD5Thompson PD Buchner D Piña IL et al.Exercise and physical activity in the prevention and treatment of atherosclerotic cardiovascular disease: a statement from the Council on Clinical Cardiology (Subcommittee on Exercise, Rehabilitation, and Prevention) and the Council on Nutrition, Physical Activity, and Metabolism (Subcommittee on Physical Activity).Circulation. 2003; 107: 3109-3116Crossref PubMed Scopus (1572) Google Scholar were offset by the presence of air pollution. Reductions in measures of arterial stiffness have been recorded with the use of guideline-directed medical therapy;6Upala S Wirunsawanya K Jaruvongvanich V Sanguankeo A Effects of statin therapy on arterial stiffness: A systematic review and meta-analysis of randomized controlled trial.Int J Cardiol. 2017; 227: 338-341Summary Full Text Full Text PDF PubMed Scopus (59) Google Scholar however, until this study, evidence has been scarce on the adverse effects of air pollution exposure on vascular function during physical activity.7Endes S Schaffner E Caviezel S et al.Is physical activity a modifier of the association between air pollution and arterial stiffness in older adults: The SAPALDIA cohort study.Int J Hyg Environ Health. 2017; 220: 1030-1038Crossref PubMed Scopus (31) Google Scholar Important to the interpretation of this study is the finding that air pollution causes phospholipid oxidation8Rao X Zhong J Maiseyeu A et al.CD36-dependent 7-ketocholesterol accumulation in macrophages mediates progression of atherosclerosis in response to chronic air pollution exposure.Circ Res. 2014; 115: 770-780Crossref PubMed Scopus (126) Google Scholar and oxidative stress (eg, by transition metals in fossil fuel combustion particles).9Lodovici M Bigagli E Oxidative stress and air pollution exposure.J Toxicol. 2011; 2011: 487074Crossref PubMed Scopus (403) Google Scholar These pathways accelerate atherogenesis and increase arterial stiffness, itself a strong predictor of cardiovascular events and all-cause mortality.10Vlachopoulos C Aznaouridis K Stefanadis C Prediction of cardiovascular events and all-cause mortality with arterial stiffness: a systematic review and meta-analysis.J Am Coll Cardiol. 2010; 55: 1318-1327Crossref PubMed Scopus (2883) Google Scholar However, one limitation of such panel studies is their size; as such, generalisability can be an issue. In view of this limitation, more and larger practical real-world exposure studies like the one done by Sinharay and colleagues4Sinharay R Gong J Barratt B et al.Respiratory and cardiovascular responses to walking down a traffic-polluted road compared with walking in a traffic-free area in participants older than 60 years with chronic lung or heart disease and age-matched healthy controls: a randomised, crossover study.Lancet. 2017; (published online Dec 5.)http://dx.doi.org/10.1016/S0140-6736(17)32643-0PubMed Google Scholar that also assess novel in-vivo biomarkers of oxidative stress and phospholipid oxidation might further clarify the mechanistic pathways and clinical implications of air pollution exposure, and broaden their known applicability. Furthermore, additional evidence on the temporal relationships and longer-term cumulative effects of chronic air pollution on arterial stiffness is also needed. Overall, however, data from Sinharay and colleagues provide significant new evidence of an important biological pathway between subclinical CVD and the systemic effects of air pollution exposure. The design used by Sinharay and colleagues is especially important in providing patient-level data for both parameters of air pollution exposure and measures of vascular function during a controlled period of physical activity. Significant increases were noted in arterial pulse wave velocity and augmentation index among the healthy volunteers that were associated with greater exposures to ultrafine particles and black carbon soot (markers of diesel vehicle emissions in this setting) but not with overall PM2.5 mass.4Sinharay R Gong J Barratt B et al.Respiratory and cardiovascular responses to walking down a traffic-polluted road compared with walking in a traffic-free area in participants older than 60 years with chronic lung or heart disease and age-matched healthy controls: a randomised, crossover study.Lancet. 2017; (published online Dec 5.)http://dx.doi.org/10.1016/S0140-6736(17)32643-0PubMed Google Scholar These new results are consistent with our past investigation in urban children with asthma, which found that a worsening of respiratory symptoms was significantly associated with personal exposures to black carbon soot, but not with PM2.5 mass.11Spira-Cohen A Chen LC Kendall M Lall R Thurston GD Personal exposures to traffic-related air pollution and acute respiratory health among Bronx school children with asthma.Environ Health Perspect. 2011; 119: 559-565Crossref PubMed Scopus (144) Google Scholar The fact that the associations were more significant for the black carbon soot and ultrafine particle components of the PM2.5 also concurs with past indications that, of the PM2.5 in the ambient air, fossil fuel combustion particles are especially important to the associations found with CVD mortality and morbidity.12Thurston G Balmes J We need to "Think Different" about particulate matter.Am J Respir Crit Care Med. 2017; 196: 6-7Crossref PubMed Scopus (6) Google Scholar The changes in arterial stiffness reported in the study by Sinharay and colleagues are biologically consistent with the air pollution and CVD health associations found in the population-based studies of hospital admissions and mortality, further strengthening the consensus that the association between particulate matter and CVD is causal. Although more studies are needed on the respective health effects of all the individual constituents and sources of PM2.5, the results of this and other recent urban studies already indicate that policy makers and health professionals should make the reduction in public exposures to diesel particulate matter a high priority in PM2.5 air pollution control and patient avoidance strategies. We declare no competing interests. Respiratory and cardiovascular responses to walking down a traffic-polluted road compared with walking in a traffic-free area in participants aged 60 years and older with chronic lung or heart disease and age-matched healthy controls: a randomised, crossover studyShort-term exposure to traffic pollution prevents the beneficial cardiopulmonary effects of walking in people with COPD, ischaemic heart disease, and those free from chronic cardiopulmonary diseases. Medication use might reduce the adverse effects of air pollution in individuals with ischaemic heart disease. Policies should aim to control ambient levels of air pollution along busy streets in view of these negative health effects. Full-Text PDF Open Access