Type 1 Diabetes Linked to Fourfold Higher Risk of Bladder Cancer: Meta-Analysis Shows

The study, by Helena Oskoui Bennett and her team from the University of Southern California Keck School of Medicine, Department of Population and Public Health Sciences, revealed that individuals with

type 1 diabetes face a markedly higher risk of developing bladder cancer, even after accounting for smoking history.

While type 2 diabetes has long been recognized as a contributor to bladder cancer risk, the potential link between type 1 diabetes and this malignancy has remained uncertain. To clarify this association, the researchers systematically reviewed and analyzed all available human studies that examined the incidence of bladder cancer among people with type 1 diabetes.

The comprehensive review identified nine independent studies providing relevant data. Notably, eight of these earlier studies did not adequately adjust for tobacco smoking—a well-established and potent risk factor for bladder cancer—which may have masked the true relationship between type 1 diabetes and cancer risk. Recognizing this gap, the researchers conducted a refined quantitative synthesis using meta-regression to account for residual confounding by smoking history, followed by a smoking-adjusted meta-analysis.

Their findings were striking:

According to the authors, the observed association had likely been previously obscured by negative confounding from smoking, as individuals with type 1 diabetes are generally less likely to smoke than the general population. By adjusting for this factor, the current study provides a clearer understanding of the true magnitude of risk.

The researchers emphasized that these findings have important clinical implications. Given the substantial elevation in risk, enhanced bladder cancer surveillance among people with type 1 diabetes may be warranted. They also highlighted the need for future research that explores how disease duration, glycemic control, and diabetes-related complications might influence cancer risk.

The meta-analysis offers robust evidence that type 1 diabetes is not only a metabolic disorder but also a potential risk factor for malignancy, particularly bladder cancer. The authors call for larger, well-designed studies to further elucidate the biological mechanisms linking type 1 diabetes and bladder carcinogenesis and to inform screening and prevention strategies for this at-risk population.

Reference:

Bennett, H. O., Bogumil, D., Kysh, L., Van den Brandt, P., Watanabe, R. M., Siegmund, K. D., & Cortessis, V. K. (2025). Systematic review and meta-analysis corrected for history of smoking tobacco identifies type 1 diabetes as a possible risk factor for bladder cancer. Diabetes Research and Clinical Practice, 112976. https://doi.org/10.1016/j.diabres.2025.112976