The full effects of passive smoking may have been underestimated

Passive smoking and risk of coronary heart disease and stroke: prospective study with cotinine measurement BMJ Online First.

The full effects of passive smoking may have been underestimated, according to a new study available on today (Wednesday 30 June).

Most studies on passive smoking have examined the risks of living with someone who smokes. Although this is an important component of exposure, it does not take account of additional exposure in workplaces and in public places (particularly pubs and restaurants). In contrast, cotinine (a by-product of nicotine) can provide a more accurate measure of exposure from all these sources.

Researchers at St George's Hospital Medical School and the Royal Free UCL Medical School examined the links between blood cotinine levels and risk of coronary heart disease (CHD) and stroke in 4,729 men from 18 British towns. The men were monitored for 20 years.

Higher concentrations of blood cotinine levels among the non-smokers were associated with a 50-60% greater risk of CHD. In earlier partner smoking studies, passive smoking is associated with a 25-30% increased risk. This suggests that the effects of passive smoking may have been underestimated in earlier studies, say the authors. The risks were particularly increased during the early follow up periods, indicating that the association between cotinine levels and CHD seems to decline with time. This suggests a further possible source of underestimation of the effects of passive smoking, as long follow up periods have been a feature of many earlier studies, they add.

Further studies of the association between cotinine (or similar biomarkers) and risk of CHD will help to assess the effects of passive smoking on cardiovascular disease with greater precision. In the meantime, these results should add to the weight of evidence suggesting that exposure to passive smoking is a public health hazard and should be minimised, they conclude.

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