Published in:
01-03-2013 | Brief report
Diabetes and risk of bladder cancer among postmenopausal women in the Iowa women’s health study
Published in: Cancer Causes & Control | Issue 3/2013
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Purpose
Studies have indicated that diabetes is a risk factor for bladder cancer; however, many failed to adjust for confounding variables. An earlier publication from the Iowa Women’s Health Study reported a positive association of baseline diabetes with bladder cancer risk between 1986 and 1998, although the number of cases was small (n = 112). We re-examined the diabetes–bladder cancer risk association by accounting for 12 more years of follow-up and assessed whether the association varied by diabetes duration, body mass index, or waist-to-hip ratio (WHR).
Methods
Proportional hazards regression was used to estimate the hazard ratio (HR) of bladder cancer (n = 277) in relation to diabetes (before enrollment and during follow-up) and diabetes duration using a time-dependent approach.
Results
In a multivariate time-dependent analysis, the HR for bladder cancer was 1.69 (95 % CI 1.40–2.41) in relation to diabetes among 37,327 postmenopausal women initially free of cancer. There was an interaction between diabetes and WHR (p = 0.01). Bladder cancer HR in diabetic women with WHR > 0.9 was 2.5 times higher than expected. There was no dose–response relation of bladder cancer risk with diabetes duration. Compared to no diabetes, HRs were 1.77, 2.03, and 1.55 for diabetes durations of ≤5, 6–10, and >10 years, respectively.
Conclusions
We confirmed a positive association between diabetes and bladder cancer risk among white postmenopausal women. We also observed a synergistic interaction between diabetes and high WHR in bladder cancer development that might be explained by increased insulin resistance and inflammation related to abdominal obesity.