Dose-years as an improved index of cumulative tobacco smoke exposure

In assessing the link between tobacco smoking and disease, it is important to determine longterm, cumulative exposure to tobacco smoke as accurately as possible. Conventional methods of assessing exposure to tobacco smoke each have intrinsic limitations. Self-reporting of tobacco use, and the conversion of this data to pack-years, can be prone to error due to individuals wishing to conceal smoking habits, inaccurate reporting of daily cigarette consumptions or years of smoking, and failure to take into account the variation that exists in inter-individual smoking experiences. Measurement of cotinine, a major metabolite of nicotine in humans, is a reliable method of monitoring recent doses of tobacco smoke exposure. Cotinine concentrations, however, may remain stable in smokers over the longer term. Therefore, dose-years, and more specifically cotinine-years, may represent an improved index of cumulative tobacco smoke exposure.