"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.
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.
The research was well reported by BBC News.
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.
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:
The researchers found:
From the modelling study, they estimated:
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.
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.