Objective: To investigate the association between cruciferous and other vegetables and thyroid cancer risk we systematically reanalyzed the original data from 11 case-control studies conducted in the US, Asia, and Europe.
Methods: A total of 2241 cases (1784 women, 457 men) and 3716 controls (2744 women, 972 men) were included. Odds ratios (OR) and the corresponding 95% confidence intervals (CI) were estimated for each study by logistic regression models, conditioned on age and sex, and adjusted for history of goiter, thyroid nodules or adenomas, and radiation. Summary ORs for all studies combined were computed as the weighted average of the estimates from each study.
Results: A decreased risk for the highest level of cruciferous vegetable intake, as compared to the lowest, was observed in Los Angeles, Hawaii, Connecticut, southeastern Sweden, Tromsø, and Switzerland; the OR were above unity in Japan and Uppsala, whereas no material association was found in northern Sweden, Italy, or Greece. The OR values for all studies combined were 0.87 (95% CI 0.75-1.01) for moderate and 0.94 (95% CI 0.80-1.10) for high cruciferous vegetables intake. The results were similar in studies from iodine-rich areas and endemic goiter areas, and were consistent when the analysis was restricted to papillary carcinomas and women. The summary OR values for vegetables other than cruciferous were 1.04 (0.88-1.22) for moderate and 0.82 (0.69-0.98) for high consumption.
Conclusions: This combined analysis indicates that cruciferous vegetables are not positively related to thyroid cancer risk. Their effect does not seem to be substantially different from that of other vegetables, which appear to be protective on this cancer.