Relationships Between Smoking Behaviors and Cotinine Levels Among Two American Indian Populations With Distinct Smoking Patterns

Abstract

Introduction: Smoking prevalence, cigarettes per day (CPD), and lung cancer incidence differ between Northern Plains (NP) and Southwest (SW) American Indian populations. We used cotinine as a biomarker of tobacco smoke exposure to biochemically characterize NP and SW smokers and nonsmokers and to investigate factors associated with variation in tobacco exposure.

Methods: American Indians (N = 636) were recruited from two different tribal populations (NP and SW) as part of a study conducted as part of the Collaborative to Improve Native Cancer Outcomes P50 project. For each participant, a questionnaire assessed smoking status, CPD, second-hand smoke exposure, and traditional ceremonial tobacco use; plasma and/or salivary cotinine was measured.

Results: Cotinine levels were (mean ± 95% confidence interval [CI]) 81.6 ± 14.1 and 21.3 ± 7.3 ng/ml among NP smokers and non-mokers, respectively, and 44.8 ± 14.4 and 9.8 ± 5.8 ng/ml among SW smokers and nonsmokers, respectively. Cotinine levels correlated with CPD in both populations (p < .0001). Cotinine ≥15 ng/ml was measured in 73.4% of NP smokers and 47.8% of SW smokers and in 19.0% of NP nonsmokers and 10.9% of SW nonsmokers. Ceremonial traditional tobacco use was associated with higher cotinine among NP smokers only (p = 0.004). Second-hand smoke exposure was associated with higher cotinine among NP non-smokers (P < 0.02). More secondhand smoke exposure was associated with smoking more CPD in both populations (p = 0.03-0.29). Linear regression modeling mirrored these findings.

Conclusions: High prevalence of smoking in the Northern Plains and high cotinine levels among nonsmokers in both regions highlights the tribal populations' risk for tobacco-related disease.

Implications: There is a high prevalence of smoking in Northern Plains American Indians. Among Northern Plains and Southwest nonsmokers, relatively high cotinine levels, representative of high tobacco exposure, suggest considerable exposure to second-hand smoke. It is critical to highlight the extent of second-hand smoke exposure among the Northern Plains and Southwest American Indians and to enhance efforts to initiate smoke-free policies in tribal communities, which are not subject to state-level polices.

Figure 1.

Association between self-reported smoking status and cotinine levels (ng/ml) among Northern Plains and Southwest smokers and nonsmokers. P values are based on Mann–Whitney tests. The number of participants included in each analysis was determined by available data. Two Northern Plains participants were excluded because they had no data on cotinine levels.

Figure 2.

Association of cotinine levels (ng/ml) and number of cigarettes smoked per day among Northern Plains (NP), Southwest (SW), and Caucasian (C) smokers. Inset graphs depict the correlation and linear regression of cotinine and cigarettes smoked per day among NP and SW smokers. P and Spearman r values are based on Spearman correlation tests or Mann–Whitney tests. The number of participants included in each analysis was determined by available data. Nine NP smokers were excluded because they did not report number of cigarettes smoked per day. All error bars represent 95% confidence intervals (CI) except those referring to cigarettes smoked per day by Caucasians; these error bars represent the interquartile range. Caucasian data were taken from St. Helen et al.

Figure 3.

Proportion of Northern Plains and Southwest smokers and nonsmokers who had cotinine levels ≥15 ng/ml. Using 3 ng/ml as the cut point, these values were 84.2% and 28.2% in Northern Plains smokers and nonsmokers (p < .0001), and 74.4% and 27.7% in Southwest smokers and nonsmokers (p < .0001), respectively. The p values are based on chi-square tests. The number of participants included in each analysis was determined by available data. Two Northern Plains participants were excluded because they had no data on cotinine levels.