Thursday, January 06, 2005

Passive pupils

'Children exposed to passive smoking are likely to do worse at school than their peers', says a report on BBC News. Researchers in Cincinnati and Rochester in the USA analysed data gathered between 1988 and 1994 on children aged six to 16 with low levels of cotinine (a marker for nicotine) in their blood, consistent with exposure to environmental tobacco smoke (ETS).

They found a significant inverse relationship between serum cotinine levels and performance on three tests of cognitive ability, with results falling by one or two points for each unit increase in cotinine levels. Amanda Sandford, research manager at Action on Smoking and Health (ASH), told the BBC: 'This shocking study strengthens the case for protecting children from second-hand smoke in all indoor environments.'

Even the lead researcher on the study accepts that, for any particular child, the levels of cognitive deficiency suggested in this study are small - but she still tries to suggest that there are wider social implications. 'These declines may not be clinically meaningful for an individual child, but they have huge implications for our society because millions of children are exposed to environmental tobacco smoke', said Dr Kimberley Yolton. But there are further problems with this study.

Correlation does not prove causation. For example, cotinine is assumed to be an accurate marker for nicotine exposure. Cotinine can also be produced by consuming certain foods, including potatoes - so the levels of cotinine in the blood may not even be solely due to tobacco smoke.

Even if there is exposure to tobacco smoke, that doesn't mean the exposure caused the difference in learning abilities. Smoking is also associated with lower levels of education, income, nutrition and so on. Children from poorer or less educated families tend to do less well on average than children from better-off families. The exact reasons for this are numerous and complex. Although the researchers claim to have allowed for many of these other factors, they admit that the differences in test results are quite small - and how can they be so sure they have controlled for these other factors correctly?

How do we know the children themselves weren't smoking? The researchers take a lot on trust: 'Children were included in the sample if their serum cotinine levels were 15 ng/mL, a level consistent with ETS exposure, and if they denied using any tobacco products in the previous five days.' Do the researchers really think that children, especially young children, will be honest about such things? The kind of kids who smoke are more likely to be the ones who don't pay attention in class, skip school altogether, and tell fibs to official-looking researchers.

This research establishes little about the relationship between smoking and the educational abilities of children. It certainly doesn't provide the kind of evidence that ASH and others are craving for to prove that we're hurting our kids by having a fag.

Exposure to Environmental Tobacco Smoke and Cognitive Abilities among U.S. Children and Adolescents, Environmental Health Perspectives, Volume 113, Number 1 January 2005