When I was a boy in London I used to love what we called pea-soupers, that is to say fogs so thick that you couldn’t see your hand in front of your face at midday. They came every November and buses, with a man walking slowly before them to guide them, would loom up suddenly out of the gloom with their headlights like the glowing eyes of monsters. It took my father so long to drive to work that by the time he arrived it was time for him to come home again. I loved those fogs, but then the government went and spoiled the fun by passing the Clean Air Act. They never returned, those wonderful, exciting fogs.
Little did I know (or care) that those wonderful, exciting fogs killed thousands by bronchitis. But many years later I got bronchitis for the first and only time in my life from breathing the polluted winter air of Calcutta. I have also traveled in Communist countries where it seemed that the only thing the factories produced was pollution. I don’t need persuading that clear air is a good thing, not only aesthetically but also from the health point of view.
Southern California used to have some of the worst air pollution in the United States, but the quality of the air in Los Angeles has improved over the last two or three decades. Researchers who reported their findings in a recent edition of the New England Journal of Medicine conducted what is called a natural experiment: they estimated the pulmonary capacity of children who grew up as the level of pollution declined.
Most research on the health effects of air pollution has concentrated on deaths from cardiovascular disease among adults, usually of a certain age. But it is known that relatively poor lung function among younger people predicts cardiovascular disease later in life quite well. There is also an association between air pollution and early death from cardiovascular disease, though of course an association does not by itself prove causation. Does air pollution cause poor lung function in children?
The researchers measured lung function in three cohorts of children, 2120 in all, aged 11 to 15, who were of those ages between 1994 and 1998, 1997 and 2001, and 2007 and 2011. During this period, atmospheric pollution in Los Angeles declined markedly, as measured by levels of nitrogen dioxide, ozone and particulate matter.
Lung function, estimated by forced expiratory volume, improved (or at any rate increased) as air pollution declined. The numbers of children with lower than predicted function declined from 7.9 percent to 6.3 percent to 3.6 percent in the three cohorts. The improvement occurred among whites and Hispanics, boys and girls, and even those with asthma, i.e. the asthmatics, were less incapacitated.
The authors thought that the improvement in lung function was likely to persist into adulthood or, to put it in a slightly less cheerful way, damage done in childhood by air pollution might be permanent. This is not quite so pessimistic as it sounds, for there is probably no age at which an improvement in the quality of the air is not capable of producing an improvement in health.
The main drawback of the study was that there was no control group, that is to say a population whose cohorts of children experienced no improvement in the quality of the air they breathed. Perhaps the function of their lungs would have shown the same improvement as well, though I rather doubt it.
One little semantic point about the paper: children aged 11 were referred to as students rather than as pupils. Perhaps this is because we nowadays expect people to grow up very quickly, but not very far.