- 2017/12/6 11:45
- Two new studies of road air pollution in London find detrimental effects on over-60s and unborn babies
6 December 2017
Exposure to air pollution on city streets is enough to counter the beneficial health effects of exercise in adults over 60, according to new research led by Imperial College London and Duke University. These findings, published in as open-access paper in The Lancet, show that short term exposure to air pollution in built-up areas such as London’s busy Oxford Street can prevent the positive effects on the heart and lungs that can be gained from walking.
Further, findings of a study led by Imperial College London researchers of more than half a million infants in the city suggests that pregnant mothers exposed to air pollution from London’s busy roads are more likely to give birth to babies that are underweight or smaller than they should be. This open-access paper is published in The BMJ.
The over-60s. The findings of this study add to the growing body of evidence showing the negative impacts of urban air pollution on cardiovascular and respiratory health. The authors say the effects could potentially apply to other age groups as well and highlight the need for stricter air quality limits and greater access to green spaces.
Previous research has found that diesel exhaust fumes, particularly fine particulate matter air pollution, has been associated with an increased risk of cardiovascular disease and death, and can cause a worsening of diseases of the airways, such as asthma.
The latest study, funded by the British Heart Foundation, is the first to show the negative effects on healthy people, people with a chronic lung condition linked with smoking called Chronic Obstructive Pulmonary Disease (COPD), and those with coronary heart disease, which affects the supply of blood to the heart.
These findings are important as for many people, such as the elderly or those with chronic disease, very often the only exercise they can do is to walk. Our research suggests that we might advise older adults to walk in green spaces, away from built-up areas and pollution from traffic.
—senior author Fan Chung, Professor of Respiratory Medicine and Head of Experimental Studies Medicine at National Heart & Lung Institute at Imperial College London
In the study, researchers recruited 119 volunteers through the Royal Brompton Hospital in London, who were over the age of 60 and were either healthy, had stable COPD, or had stable heart disease. Patients walked for two hours in two London settings at midday; in a relatively quiet part of leafy Hyde Park and along a busy section of Oxford Street—which has regularly breached air quality limits set by the World Health Organization.
Physical measurements were taken before and after the walks to show the effects of the exercise on cardiovascular health, including measurements of lung volume exhaled, blood pressure, and the degree to which the blood vessels could expand. Environmental measurements were also collected, to track pollution levels and volunteers’ exposure. Data analysis was carried out at the MRC-PHE Centre for Environment and Health at Imperial College London and Kings College London, and the Rutgers School of Public Health in New Jersey.
As expected, noise and pollution levels were significantly higher on Oxford Street compared to Hyde Park, including increased measures of black carbon, nitrogen dioxide and fine particulate matter.
Analysis revealed that all participants benefitted from a stroll in the park, with lung capacity improving within the first hour and a significant lasting increase for more than 24 hours in many cases. By comparison, a walk along Oxford Street led to only a small increase in lung capacity in participants, far lower than recorded in the park.
Blood flow also increased after exercise, with decreases in blood pressure and an increase in heart rate.
Arteries became less stiff in those walking in Hyde Park with a maximum change from baseline of more than 24% in healthy and COPD volunteers, and more than 19% in heart disease patients.
This effect was drastically reduced when walking along Oxford Street, however, with a maximum change in arterial stiffness of just 4.6% for healthy volunteers, 16% for those with COPD and 8.6% for heart disease.
In addition, the researchers found that for those patients with heart disease, taking medication that improved the cardiovascular system was associated with a stabilizing effect, and may prevent them from deteriorating in areas with higher levels of air pollution.
Implications for urban planning. The authors add that it is possible that stress could account for some of the physiological differences seen between the two settings, with the increased noise and activity of Oxford Street having an effect. They also emphasize that while the study only involved two relatively short walks, the findings suggest that repeated exposures to air pollution would not be beneficial to our respiratory and cardiovascular systems.
Based on the available evidence, the authors say the findings could have implications for urban planning, including traffic control measures and access to green spaces in cities.
It is possible that studies such as this could support new air quality limits, it shows that we can’t really tolerate the levels of air pollution that we currently find on our busy streets. For people living in the inner city it may be difficult to find areas where they can go and walk, away from pollution. There may be a cost associated as they have to travel further away from where they live or work.
These are issues that mean we really need to reduce pollution by controlling traffic. That should allow everyone to be able to enjoy the health benefits of physical activity in any urban environment.
The unborn. According to the authors, cutting the average concentration of fine particle pollution emitted by the city’s road traffic by just 10% could prevent around 90 babies a year (3% of cases) being born with low birth weight.
They add that the findings could be applicable to other cities in the UK and across Europe with comparable levels of road traffic pollution, highlighting the need for environmental health policies to improve air quality in urban areas.
Previous studies have shown a link between air pollution, pregnancy complications and childhood illness, but studies of noise pollution in pregnancy have provided conflicting results.
In the latest study, published in The BMJ, the group led by Imperial College London looked at the link between exposure to air and noise pollution from road traffic during pregnancy and the effect on measures of birth weight—both low birth weight (less than 2500 g) and being born small for gestational age.
Carried out at the MRC-PHE Centre for Environment and Health at Imperial College London and Kings College London, the research focused on records of more than half a million (540,365) babies born in the Greater London area between 2006 and 2010, along with the mother’s home address location.
Using air quality data from a government emissions database, the researchers estimated average monthly concentrations of pollutants related to road traffic, including nitrogen dioxide (NO2 ), nitrogen oxides (NOx), and fine particulate matter (PM2.5) from traffic exhaust and non-exhaust sources, such as brakes or tire wear, as well as larger particulate matter (PM10). Average day and night-time road traffic noise levels were also estimated.
Analyzing the data, they found higher levels of these air pollutants, particularly PM2.5, were associated with 2% to 6% increased odds of low birth weight and 1% to 3% increased odds of being small for gestational age.
Our study has shown that a small but significant proportion of babies born underweight in London are directly attributable to exposure to air pollution, particularly to small particles produced by road traffic. Babies born with low birth weight or who are small for their gestational age, are at increased risk of dying within their first month, as well as diseases in later life, such as cardiovascular disease. Any policies aimed at reducing road traffic pollution in urban environments could therefore help to reduce the health impact on unborn babies and their life-long disease risk.
—Dr Mireille Toledano, from the School of Public Health at Imperial and senior author of the research
The researchers noted that the study’s limitations include the potential for some misclassification of exposure—for example, because exposure was estimated at the mother’s residential address, and did not account for exposure at other locations—and that estimates were used for some other risk factors, such as passive smoking in the home.
However, the researchers are confident the study data are robust and provide evidence for policymakers in the UK.
Noise role unconfirmed. They explain that while effects of traffic noise cannot be ruled out, the evidence of an association between exposure to air pollution and the poor health of unborn babies in the urban environment is clear, even though the biological mechanisms of road traffic pollution on public health are not fully understood.
To our knowledge, this is the largest study in the UK to look at the effects of air pollution on birth weight, and the largest study worldwide to look at the effect of noise exposure on birth weight. While the research did not show an independent effect of noise on birth weight, we cannot rule it out as a potential factor.
What is clear, however, is the effect that air pollution generated by road traffic is having on foetal development. We have shown that exposure during pregnancy to traffic pollution is having a detrimental effect on the health of babies in Greater London.
—Dr Rachel Smith, School of Public Health and lead author
This research was supported by the UK Natural Environment Research Council, the Medical Research Council, the Economic and Social Research Council, the Department of Environment, Food and Rural Affairs, and the Department of Health, through a cross-research council Environmental Exposures & Health Initiative, with further support from Public Health England and the National Institute for Health Research.
Sinharay, Rudy et al. (2017) “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 study” The Lancet doi: 10.1016/S0140-6736(17)32643-0
Smith Rachel B, Fecht Daniela, Gulliver John, Beevers Sean D, Dajnak David, Blangiardo Marta et al. (2017) “Impact of London’s road traffic air and noise pollution on birth weight: retrospective population based cohort study” BMJ 359 :j5299 doi: