Tuesday October 21 2014
Secondhand smoke is a risk factor for lung disease
"Living with smoker 'as bad as living in polluted city'," BBC News reports. Scottish researchers have estimated that the level of fine particulate matter (PM2.5) in smokers' households is similar to those found in a heavily polluted city such as Beijing.
PM2.5 are tiny particles less than two and a half microns wide that are components of air pollution. Because of their size, they are able to penetrate the lungs' defences against external foreign bodies, potentially causing damage. They have been linked to chronic respiratory conditions such as asthma and even lung cancer.
Researchers found, on average, PM2.5 concentrations from smokers' homes were about 10 times higher than those found in non-smoking homes. If smoking households became non-smoking, most non-smokers would have their PM2.5 intake cut by more than 70%.
Over a lifetime, the researchers calculated that PM2.5 intake from living with a smoker could be equivalent to living in a heavily polluted city, and could have the health problems associated with such an environment. For example, there has been a dramatic rise in reported asthma cases in urban areas of China.
Ideally, if you smoke, you should quit now for the benefit of your health and the health of others. If you are unable or unwilling to do so, smoke outdoors, especially if you are sharing the house with children. Simply blowing the smoke out of a window will still lead to an increase in PM2.5.
Where did the story come from?
The study was carried out by researchers from the University of Aberdeen and the Institute of Occupational Medicine in Edinburgh.
No funding was reported, but the study used data from other studies that had been funded by the Big Lottery Fund, the Irish Environmental Protection Agency and the Scottish School of Public Health Research.
It was published in the peer-reviewed public health journal Tobacco Control. This article was open-access, meaning it can be accessed and read for free.
The research was well reported by BBC News.
What kind of research was this?
This study brought together data from four previous cross-sectional studies that had measured PM2.5 concentrations in smoking and non-smoking households in Scotland. These concentrations were then used to model daily and lifetime PM2.5 intake.
Cross-sectional studies take data at one point in time, so they cannot prove cause and effect.
However, homes where there was likely to be a significant additional source of PM2.5 (for example, a coal or solid-fuel fire) were excluded from the analysis.
It is therefore probable that the tenfold difference seen between PM2.5 concentrations in smokers' and non-smokers' houses was a result of smoking.
What did the research involve?
The researchers used data from four studies conducted between 2009 and 2013, which had measured PM2.5 concentrations in a total of 93 smoking and 17 non-smoking households in Scotland. They combined this information with data on typical breathing rates and activity patterns.
Using this information, the researchers estimated:
- daily PM2.5 intake
- the percentage of total PM2.5 inhaled within the home environment
- the percentage reduction in daily intake that could be achieved by switching to a smoke-free home
What were the basic results?
The researchers found:
- the average PM2.5 concentration was 31 micrograms per cubic metre (µg/m3) in smoking homes
- the average PM2.5 concentration was 3µg/m3 in non-smoking homes
From the modelling study, they estimated:
- PM2.5 intake for a two-year-old child would be 34µg/day in a non-smoking home and 298µg/day in a smoking home. If a smoking home became a non-smoking home, PM2.5 intake would reduce by 79%.
- PM2.5 intake for an 11-year-old child would be 45µg/day in a non-smoking home and 291µg/day in a smoking home. If a smoking home became a non-smoking home, PM2.5 intake would reduce by 76%.
- PM2.5 intake for a 40-year-old would be 59µg/day in a non-smoking home and 334µg/day in a smoking home. If a smoking home became a non-smoking home, PM2.5 intake would reduce by 74%.
- PM2.5 intake for a 70-year-old housebound adult would be 27µg/day in a non-smoking home and 479µg/day in a smoking home. If a smoking home became a non-smoking home, PM2.5 intake would reduce by 86%.
The researchers then estimated lifetime intake. They calculated the average lifetime intake of PM2.5 for people living in non-smoking households in Scotland is 0.76g, while the average lifetime intake for those living in a smoking household (but not smoking themselves) is more than seven times that amount, at 5.82g.
They calculated that some non-smokers living with a smoker will actually inhale more PM2.5 than non-smokers living in heavily polluted urban settings.
How did the researchers interpret the results?
The researchers concluded that, "Fine particulate pollution in Scottish homes where smoking is permitted is approximately 10 times higher than in non-smoking homes. Taken over a lifetime, many non-smokers living with a smoker inhale a similar mass of PM2.5 as a non-smoker living in a heavily polluted city such as Beijing.
"Most non-smokers living in smoking households would experience reductions of over 70% in their daily inhaled PM2.5 intake if their home became smoke-free. The reduction is likely to be greatest for the very young and for older members of the population because they typically spend more time at home."
This study has found that, on average, fine particulate pollution (PM2.5) concentrations from smoking households were about 10 times those found in non-smoking homes.
The combined results of the modelling studies suggested most non-smokers would have their PM2.5 intake cut by more than 70% if smoking households quit the habit.
Over a lifetime, the researchers calculated PM2.5 intake from living with a smoker could be the equivalent of living in a heavily polluted city.
The generalisability of these results depends on how representative the smoking and non-smoking homes were of the general population.
The researchers note there were wide differences in the PM2.5 concentrations measured in different studies, which they state is probably a result of differences in the populations the samples were drawn from.
They say it is possible smokers living with children restrict their children's exposure to secondhand smoke, so these results may not be generalisable.
In any case, there are many benefits to stopping smoking and there is no justification to subjecting children to the risks of smoke exposure, even if steps are taken to mitigate this.
Read more about how Cecelia Elliott, a young mother, managed to successfully quit smoking for the sake of her son.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.