Dietary Isothiocyanates, Glutathione S-Transferase M1 (GSTM1), and Lung Cancer Risk in African Americans and Caucasians from Los Angeles County, California

Abstract

Isothiocyanates, found in cruciferous vegetables, are anticarcinogenic. Racial differences in smoking do not fully account for the African-American excess lung cancer incidence. African Americans consume more cruciferous vegetables than U.S. Whites. Impact on lung cancer risk is unknown. The glutathione S transferase M1 (GSTM1) gene promotes urinary isothiocyanate excretion. We evaluated dietary isothiocyanates and lung cancer using a population-based case-control study of 933 African Americans and Caucasians (non-Hispanic U.S. White) from Los Angeles County, California (311 cases; 622 controls). Broccoli, cauliflower, greens, and cabbage food-frequency variables represented isothiocyanates. Isothiocyanates were protective for lung cancer risk. Adjusted odds ratio (OR) for the uppermost quartile > 80 μ mol isothiocyanates/wk, compared to lowest, was 0.65 [95% confidence interval (CI) = 0.41–1.00, trend P = 0.02]. Association was stronger among subjects with homozygous deletion of GSTM1 (OR = 0.52, 95% CI = 0.31–0.86) than subjects with at least one GSTM1 copy (OR = 0.77, 95% CI = 0.49–1.21). The difference was not statistically significant (P = 0.16). Despite African Americans consuming more cruciferous vegetables, the isothiocyanate association did not vary by race (P = 0.52). Reduced lung cancer risk with higher isothiocyanate intake may be slightly stronger among subjects with deletion of GSTM1.

ACKNOWLEDGMENTS

Conduct of the case-control study performed at the University of Southern California was funded by the California Tobacco Related Disease Research Program (TRDRP) grants, 1RT-140 and 3RT-403, to Dr. London. Data analysis performed at the University of California at Los Angeles was supported by TRDRP grant 11IT-0082 to Dr. Carpenter. Dr. Carpenter was supported by NCI P01-CA42710. Dr. London is supported by the Division of Intramural Research, National Institute of Environmental Health Sciences, National Institute of Health (ZO1 ES49017). The collection of cancer incidence data used in this study was supported by the California Department of Health Services as part of the statewide cancer reporting program mandated by California Health and Safety Code Section 103885; the National Cancer Institute's Surveillance, Epidemiology and End Results Program under contract N01-PC-35136 awarded to the Northern California Cancer Center, contract N01-PC-35139 awarded to the University of Southern California, and contract N02-PC-15105 awarded to the Public Health Institute; and the Centers for Disease Control and Prevention's National Program of Cancer Registries under agreement #U55/CCR921930-02 awarded to the Public Health Institute. The ideas and opinions expressed herein are those of the author(s), and endorsement by the State of California, Department of Health Services, the National Cancer Institute, and the Centers for Disease Control and Prevention or their contractors and subcontractors is not intended nor should be inferred.

Notes

^a Abbreviation is as follows: GSTM1, glutathione S transferase M1.

^b Cruciferous vegetables include broccoli, cabbage, cauliflower, greens, and brussels sprouts.

^a Abbreviations are as follows: ITC, isothiocyanate; GSTM1, glutathione S-transferase M1; OR, odds ratio; CI, confidence interval.

^b Adjusted for matching factors: age, ethnicity, gender.

^c Adjusted for matching factors, natural logarithm of pack years plus natural logarithm of years since quitting multiplied by natural logarithm of pack years.

^d Dietary ITC consumption divided at median value among controls.

^e Test for homogeneity reflects log likelihood ratio tests of model with product term evaluated against model without product term.

^f Term for gender omitted from model.

^g Term for ethnicity omitted from model.

^a Cruciferous vegetables include broccoli, cabbage, cauliflower, brussels sprouts, and greens.

^b Adjusted for gender.

∗P ≤ 0.05.