Obesity and risk of bladder cancer: a dose-response meta-analysis of 15 cohort studies

Abstract

Background: Epidemiological studies have reported inconsistent association between obesity and risk of bladder cancer, and the dose-response relationship between them has not been clearly defined.

Methods: We carried out a meta-analysis to summarize available evidence from epidemiological studies on this point. Relevant articles were identified by searching the PubMed and Web of Science databases through September 30, 2014. We pooled the relative risks from individual studies using random-effect model, and the dose-response relationship was estimated by using restricted cubic spline model.

Results: Fifteen cohort studies with 38,072 bladder cancer cases among 14,201,500 participants were included. Compared to normal weight, the pooled relative risks and corresponding 95% confidence intervals of bladder cancer were 1.07(1.01-1.14) and 1.10(1.06-1.14) for preobese and obesity, with moderate (I² = 37.6%, P = 0.029) and low (I² = 15.5%, P = 0.241) heterogeneities between studies, respectively. In a dose-response meta-analysis, body mass index (BMI) was associated with bladder cancer risk in a linear fashion (P(non-linearity) = 0.467) and the risk increased by 4.2% for each 5 kg/m2 increase. No significant publication bias was found (P = 0.912 for Begg's test, P = 0.712 for Egger's test).

Conclusions: Findings from this dose-response meta-analysis suggest obesity is associated with linear-increased risk of bladder cancer.

Fig 1. Flow diagram of the study selection for the meta-analysis.

Fig 2. Forest plot of preobese and risk of bladder cancer.

Squares indicate study-specific relative risks (size of the square reflects the study-specific statistical weight, i.e., the inverse of the variance); horizontal lines represent 95% CIs; the diamond indicates the summary relative risk estimate with its 95% CI. CI, confidence interval.

Fig 3. Forest plot of obesity and risk of bladder cancer.

Squares indicate study-specific relative risks (size of the square reflects the study-specific statistical weight, i.e., the inverse of the variance); horizontal lines represent 95% CIs; the diamond indicates the summary relative risk estimate with its 95% CI. CI, confidence interval.

Fig 4. Dose-response relationships between body mass index and the relative risk of bladder cancer.

Shaded area represents 95% confidence limits for fitted curve. P = 0.467 for non-linearity, which indicates no curvilinear association.