Obesity and Risk of Bladder Cancer: A Dose-Response Meta-Analysis of 15 Cohort Studies

Abstract

BackgroundEpidemiological studies have reported inconsistent association between obesity and risk of bladder cancer, and the dose-response relationship between them has not been clearly defined.MethodsWe 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.ResultsFifteen 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).ConclusionsFindings from this dose-response meta-analysis suggest obesity is associated with linear-increased risk of bladder cancer.

Influence of diabetes on the risk of urothelial cancer according to body mass index: A 10-year nationwide population-based observational study

“…A recent meta-analysis from 16 cohort studies suggested a linear relationship between BMI and risk of urothelial cancer [20]. However, the relation between BMI and the percentage of body fat depends on age and sex, and differs across ethnic groups [8].…”

Excess Weight as a Risk Factor Common to Many Cancer Sites: Words of Caution when Interpreting Meta-analytic Evidence

“…In the Sun et al (11) meta-analysis, the extracted point estimates relative to normal weight from Song et al (12) for BMI categories 25.0 to 27.4; 27.5 to 29.9; 30.0 to 34.9; and greater than or equal to 35.0 kg/m 2 for men were: 1.48; 1.95; 1.47, 1.91 and for women were: 2.59, 2.69; 2.63, 1.93. Yet, the continuous BMI plots in Figure 1 of Song et al (12) indicate that the BMI-risk relation was absolutely null with risk near 1.00 across the full BMI range.…”

“…Thus, during evaluation, the IARC working group referred to the WCRF bladder cancer report based on 22 prospective cohort studies, which reported no significant association with between obesity and bladder cancer incidence (9). But two additional meta-analyses of prospective cohort studies (10, 11), searching very similar timeframes, identified substantially different study numbers. These analyses reported significant positive associations and (and in contrast to the WCRF analysis) concluded that BMI was associated with an increased risk of bladder cancer (Table 1).…”

“…These analyses reported significant positive associations and (and in contrast to the WCRF analysis) concluded that BMI was associated with an increased risk of bladder cancer (Table 1). On closer scrutiny, these differences partly reflect obscure decisions about study inclusion (despite that the design type was restricted to prospective studies) and, in the meta-analysis by Sun and colleagues (11), the summary estimate may have been disproportionally influenced by an incorrect data extraction of risk estimates from one study (12). In addition, one large analysis from the EPIC cohort (13), reporting a mildly elevated risk of bladder cancer in overweight when compared with normal weight men, was not included in the systematic review by Sun and colleagues (11) that searched within the timeframe of this publication (epub date: 29 April 2014).…”

“…On closer scrutiny, these differences partly reflect obscure decisions about study inclusion (despite that the design type was restricted to prospective studies) and, in the meta-analysis by Sun and colleagues (11), the summary estimate may have been disproportionally influenced by an incorrect data extraction of risk estimates from one study (12). In addition, one large analysis from the EPIC cohort (13), reporting a mildly elevated risk of bladder cancer in overweight when compared with normal weight men, was not included in the systematic review by Sun and colleagues (11) that searched within the timeframe of this publication (epub date: 29 April 2014). In a similar manner, a recently published meta-analysis (14) evaluating the association between BMI and cervical cancer risk identified only nine studies (Table 1), yet the IARC handbook group search, over a similar timeframe, identified fourteen studies (listed in supplemental material).…”