Abstract 2824: A prospective evaluation of dietary indole-3-carbinol in relation to risk of lung cancer in the Singapore Chinese Health Study

Abstract

Abstract Background: Indole-3-carbinol (I3C) is a naturally occurring hydrolysis product of glucobrassicin, a glucosinolate found in cruciferous vegetables. I3C has been shown to inhibit carcinogen-induced occurrence of cancer in multiple organs including lung in experimental animals. High consumption of dietary glucobrassicins was inversely related to urinary levels of NNAL, a metabolite of the tobacco-specific lung carcinogen NNK. Data on the dietary intake of I3C or its precursors and lung cancer risk in humans are lacking. Methods: We prospectively examined the association between dietary intake of glucobrassicins and risk of lung cancer in the Singapore Chinese Health Study, a cohort of 63,257 middle-aged and older Chinese men and women enrolled between 1993 and 1998. Dietary intake of glucobrassicins was derived from a validated, semi-quantitative food-frequency questionnaire administered to subjects in person at enrollment and the quantified amount of glucobrassicin in specific cruciferous vegetables purchased from Singapore markets. We had complete follow-up for incidence of cancer and death among cohort participants through computer record linkage analysis to the nation-wide Singapore cancer and death registries. As of December 31, 2007, 1,104 incident cases of lung cancer were identified within the cohort. Cox proportional hazards regression was used to evaluate the association between dietary intake of glucobrassicins and lung cancer risk. The regression model included age, body mass index (kg/m2), year of interview, gender, dialect group, level of education, smoking status, number of cigarettes/day and years of cigarette smoking, dietary intake of beta-cryptoxanthin, and total calorie intake. Results: After adjustment for number of cigarettes/day, number of years of smoking and other potential confounders, current smokers with high intake of glucobrassicins had a borderline statistically significant reduced risk of lung cancer (Ptrend=0.08). Compared to the lowest quartile, hazard ratios (HR) [95% confidence intervals (CI)] for the 2nd, 3rd, and 4th quartile of glucobrassicins were 0.94 (0.77-1.15), 0.95 (0.76-1.18) and 0.77 (0.59-0.99), respectively. This inverse association was more evident after excluding the first 5-years of follow-up; the corresponding HR (95% CI) were 0.89 (0.70-1.14), 0.93 (0.72-1.21) and 0.61 (0.44-0.85) (Ptrend=0.01). The present study did not show an inverse association between dietary isothiocyanate (ITC) intake and lung cancer in current smokers. Neither I3C precursors nor ITC was related to risk of lung cancer in never or former smokers. Conclusion: High intake of dietary glucobrassicins was associated with reduced incidence of lung cancer in smokers. The findings of this study suggest that I3C precursors rather than ITC present in cruciferous vegetables may exert a protective role in the development of lung cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2824.