Meta-analysis in the association between obesity and risk of thyroid cancer.

Although many epidemiologic studies have investigated obesity and thyroid cancer risk, definite conclusions cannot be drawn. To clarify the effects of obesity on the risk of thyroid cancer, a meta-analysis was performed. Related studies were identified from PubMed, Springer Link, Ovid, Chinese Wanfang Data Knowledge Service Platform, Chinese National Knowledge Infrastructure (CNKI), and Chinese Biology Medicine (CBM) till 16 Aug 2014. Pooled RRs and 95% CIs were used to assess the strength of the associations. A total of 16 studies including 12616154 subjects were involved in this meta-analysis. A significantly elevated thyroid cancer risk was found in overall analysis (RR = 1.29, 95% CI 1.20-1.37, P < 0.00001). In the gender subgroup analyses, a statistically significant association was found in male patients (RR = 1.35, 95% CI 1.16-1.58, P = 0.0001) and in female patients (RR = 1.29, 95% CI 1.19-1.40, P < 0.00001). When we limited the meta-analysis to studies that controlled for age (RR = 1.34, 95% CI 1.24-1.44, P < 0.00001), smoke (RR = 1.36, 95% CI 1.22-1.52, P < 0.00001), alcohol use (RR = 1.40, 95% CI 1.15-1.71, P = 0.0009), and history of benign thyroid disease (RR = 1.51, 95% CI 1.24-1.83, P < 0.0001), a significant association between obesity and thyroid cancer risk remained. This meta-analysis provides the evidence that obesity may contribute to the thyroid cancer development.