People with type 1 diabetes are at a much higher risk of developing bladder cancer than previously believed. This conclusion comes from researchers at the University of Southern California’s Keck School of Medicine, who conducted the first systematic study that properly accounted for the impact of smoking — the main risk factor for this disease. The work was published in Diabetes Research and Clinical Practice (DRCP).
About half of all bladder cancer cases are caused by smoking. The remaining causes are still poorly understood. Earlier studies hinted at a possible link between type 2 diabetes and bladder cancer, but no such association had been found for type 1 diabetes — until now.
According to the authors, all previous studies shared a major flaw: none of them reliably controlled for smoking. This is critical because tobacco is a powerful risk factor for bladder cancer, and without accounting for it, it is impossible to separate the effect of diabetes from the effect of smoking.
The researchers hypothesized that people with type 1 diabetes may smoke less than the general population, since they grow up with a serious chronic condition and often follow healthier lifestyles. This could have “masked” the impact of diabetes itself.
To test this hypothesis, the study’s lead author, public health researcher Helena Oskoui Bennett, compiled data on smoking prevalence in the countries where the original studies were conducted, including information from the WHO. The analysis confirmed that differences in smoking rates indeed obscured the true risk. After adjusting for smoking, it became clear that people with type 1 diabetes develop bladder cancer 4.29 times more often.
The biological mechanisms behind this link remain unclear, but the authors suspect that type 1 diabetes may alter cellular and tissue processes in ways that promote tumor development. If so, careful glucose control and effective disease management might help reduce the risk. The researchers also do not rule out that diabetes and smoking may amplify each other’s harmful effects.
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