Abstract
OBJECTIVE: A cross-sectional population-based study was conducted to assess, in active smokers, the relationship of number of cigarettes smoked and other characteristics to salivary cotinine concentrations. METHODS: A random sample of active smokers aged 15 years or older was selected using a stepwise cluster sample strategy, in the year 2000 in Rio de Janeiro, Brazil. The study included 401 subjects. Salivary cotinine concentration was determined using gas chromatography with nitrogen-phosphorus detection. A standard questionnaire was used to collect demographic and smoking behavioral data. The relation between the number of cigarettes smoked in the last 24h and cotinine level was examined by means of a nonparametric fitting technique of robust locally weighted regression. RESULTS: Significantly (p<0.05) higher adjusted mean cotinine levels were found in subjects smoking their first cigarette within five minutes after waking up, and in those smoking 1-20 cigarettes in the last 24h who reported inhaling more than ½ the time. In those smoking 1-20 cigarettes, the slope was significantly higher for those subjects waiting for more than five minutes before smoking their first cigarette after waking up, and those smoking "light" cigarettes when compared with their counterparts. These heterogeneities became negligible and non-significant when subjects with cotinine >40 ng/mL per cigarette were excluded. CONCLUSIONS: There was found a positive association between self-reporting smoking five minutes after waking up, and inhaling more than ½ the time are consistent and higher cotinine levels. These can be markers of dependence and higher nicotine intake. Salivary cotinine proved to be a useful biomarker of recent smoking and can be used in epidemiological studies and smoking cessation programs.
Highlights
Nicotine has a short half-life and its major metabolite is cotinine
Significantly (p
In those smoking 1–20 cigarettes, the slope was significantly higher for those subjects waiting for more than five minutes before smoking their first cigarette after waking up, and those smoking “light” cigarettes when compared with their counterparts
Summary
Nicotine has a short half-life and its major metabolite is cotinine. Cotinine has a half-life of 16–20 hours and is a useful indicator of nicotine intake from recent smoking. Factors potentially influencing cotinine levels relate to the product smoked (filter or non-filter and nicotine yield), the way the product is smoked (depth of inhalation and butt length), and smoker characteristics (age, gender, and phenotype of nicotine metabolism).[15] Cotinine levels vary across racial groups, perhaps reflecting differences in some of these factors.[3,10] These racial differences are of interest and may reflect intrinsic metabolic differences, differences related to the circumstances of exposure, such as frequency and depth of smoking,[3,22] or differential accuracy in self-reported number of cigarettes smoked recently.[1] The heterogeneity of effects by ethnic background suggests that other variables may modify the observed relationship between number of cigarettes smoked and cotinine concentration. If this is the case, these variables would have to be taken into consideration when assessing the value of cotinine as a marker of recent smoking exposure
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