SCIENCE FRIDAY: UNHEALTHY WALK ROUTES

Street and bridge traffic in NYC, view from The Bentley Hotel. Taken by PKSenagore December 5, 2017. All rights reserved.

NOT ALL WALKS ARE EQUAL There’s evidence that the health benefits gained from getting walking exercise may be dependent on location.  A study published in the British medical journal, The Lancet, indicated that walking on heavily polluted streets may “CANCEL OUT” such improvements, especially in persons 60 or more years of age with pre-existing heart and lung disease.
 
Scientists from the National Heart and Lung Institute and MRE-PHE Centre for Environment and Health, Imperial College, London UK recruited 40 healthy volunteers, 40 with stable Chronic Obstructive Lung Disease (COPD) and 39 with stable ischemic heart disease, all aged 60 and older, to participate. All had abstained from smoking for at least 12 months prior to the study. Each person was randomly assigned to walk about 5k along one (they picked numbered discs from a bag), then the other, of two paths: a nearly traffic-free green area in Hyde Park or a nearby HEAVILY trafficked street filled mostly with diesel-powered taxi cabs and buses.  Participants walked their own ‘normal’ pace for about 2 hours, from 11am to 1pm up and down the route.  Each walk was separated by 3-8 weeks.
 
Heart and lung health outcome data, including measures of lung function, respiratory resistance, and arterial stiffness was collected at baseline and various time points after each location walk, up to 26 hours.  A questionnaire was used to record participant symptoms of cough, sputum, wheeze, shortness of breath at the start of each walk and after 2, 4, 6, and 26 hours. Environmental exposure data was also collected from each route: levels of noise, black carbon, particulate matter concentrations, ultrafine matter, and nitrogen dioxide levels.
 
Levels of noise and the concentrations of pollutants were all measured as HIGHER on busy Oxford Street than in the green Hyde Park area.
 
“In ALL participants, irrespective of disease status, walking in Hyde Park resulted in improvements” in measures of lung function and arterial stiffness.  “By contrast these improvements were attenuated (lessened) after walking on Oxford Street”. The researchers indicated that a “similar phenomenon” was noted in participants with COPD and heart disease. Persons with COPD reported more respiratory difficulty on Oxford Street, like cough, sputum, shortness of breath, and wheeze.
 
The interpretation was that short-term exposure to traffic pollution PREVENTS the beneficial cardiopulmonary effects of walking in persons with COPD, ischemic heart disease, and even those without these diseases.
 
The researchers admit that their short-term study was not able to “inform” on the long-term benefits of exercise in relation to pollution.  It’s possible that regular moderate exercise could protect against the effects of air pollution. “Data from other studies suggest that air pollution risks do not overcome the benefits of active walking in urban areas using all-cause mortality outcomes”. But the scientists felt that results supported the widely-held view that traffic-related air pollutants emitted from fossil fuel combustion are “particularly toxic for individuals with cardiovascular or pulmonary diseases”.   
 
The specifics of this research study were quite complicated. The general conclusions made by the authors include:

• “Healthy participants and those with COPD and ischemic heart disease should avoid highly polluted areas to walk in if the benefits of walking are to be fully reaped.
• Older adults and chronic pulmonary and cardiac participants should be advised that exercise such as walking should be done in urban green space areas away from high density traffic or in indoor facilities with effective air filtration if located near polluted streets.
• Finally, it is important to impose policies and measures that can reduce traffic pollution so that every individual can enjoy the health benefits of physical exercise.”

 
What does Earned Runs think urban walkers might take from this study that wasn’t discussed in general? Even if you're not 60 years of age or older?
 
First, we learn that even strolling at a comfortable pace can improve some aspects of cardiovascular health both in people without and with some heart and lung diseases. This study did not require participants to walk at a specific level of perceived exertion; at the very slowest about 1.5 miles were covered per hour, which is roughly a 40-minute mile pace).
 
Second, that if walkers have some degree of choice in where they stroll, the health benefit is likely to be greater if the selected location has lower levels of traffic, especially for older persons with pre-existing lung or heart disease. The two routes in the study were near each other, but one was a green space and the other a busy, commercial street.  It could be that a 1-2 block distance in a large city might be the difference between heavy and light pollution levels, with park spaces at the very top of the ‘light’ list. 
 
Thus, for exercise it may be wiser to walk around a single ‘green’ block multiple times than follow a long route with variable adjacent traffic. To walk in areas of a popular park from which vehicles are restricted. To walk the dog during times of the day when diesel-powered traffic is not likely to be heavy.
 
Third, it indicates that park and green spaces are vital to urban life and work.  Persons in all income levels and living and working situations will benefit from nearby natural areas. Studies might investigate whether recent trends to create urban bike path lanes have an additional positive effect to decrease pollution.  Or if adding trees and plantings along these routes cleans the air. At the very least regular environmental surveillance of known heavy walk routes might help city dwellers, commuters, and workers make heathier choices, at various times of the day, as to where they walk.
 
This study will change my walking habits.  I’ll be thinking a bit more about specifically where and when I choose to go outside for exercise or walk ‘as a mode of transportation’ within a city.
 
RUN HAPPY!

“Respiratory and cardiovascular responses to walking down a traffic-polluted road 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 randomized cross-over study” Sinharay R, Gong J, Barratt B, et al.
 
http://www.thelancet.com/pdfs/journals/lancet/PIIS0140-6736(17)32643-0.pdf