Diabetes Associated With Higher Bladder Cancer Risk

People with type 1 diabetes, formerly known as juvenile diabetes, face a 4.29-fold higher likelihood of developing bladder cancer, according to a systematic review and meta-analysis conducted at the Keck School of Medicine of the University of Southern California (1^✔ ✔Trusted Source
Systematic review and meta-analysis corrected for history of smoking tobacco identifies type 1 diabetes as a possible risk factor for bladder cancer

Go to source). The analysis, published in Diabetes Research and Clinical Practice, is the first to adjust for the impact of tobacco smoking, a major factor that likely concealed the true magnitude of risk in prior research.

Bladder cancer affects roughly 2% of people in the United States. Cigarette smoking accounts for about half of bladder cancer cases across the United States and Europe, yet the causes behind the remaining cases remain unclear.

Although recent evidence has suggested that type 2 diabetes could play a role, years of epidemiological investigations did not reveal a connection between type 1 diabetes and bladder cancer.

Smoking Masks Diabetes-Related Cancer Risk

The new work explains why a potential association may have gone unnoticed. Since smoking is a strong contributor to bladder cancer, studies aimed at evaluating other risk contributors must adjust for or separate smoking’s effects from those of any proposed factor. However, none of the earlier investigations on type 1 diabetes and cancer had accounted for this.

Among nine original studies and one prior meta-analysis conducted before this new evaluation, none had properly controlled for smoking.

After examining the limitations in those datasets and correcting for them, the researchers identified a clear and consistent pattern revealing markedly higher bladder cancer risk among people with type 1 diabetes, said Victoria K. Cortessis, Ph.D., clinical professor of population and public health sciences at the Keck School of Medicine and senior author of the work.

Guidance for Patients and Missing Data

These updated findings shed light on possible origins of bladder cancer and may inform decisions made by individuals with type 1 diabetes and their clinicians. For instance, quitting or avoiding smoking could be especially critical for this group, Cortessis noted.

For many years, studies following people with type 1 diabetes reported no heightened bladder cancer risk and closer review shows the reason. Most datasets on type 1 diabetes originated from long-term follow-up studies designed to understand how the condition influenced hospitalizations and early complications. Smoking information was either never gathered or collected only once without future updates.

Impact of Unmeasured Smoking Patterns

In later years, researchers attempted to use those same datasets to explore new questions, such as whether type 1 diabetes raised the risk of other diseases like bladder cancer in adulthood. They compared disease patterns in people with type 1 diabetes with those of the general population and concluded there was no increased risk.

The flaw in this approach lay in the absence of reliable smoking data for both groups. Because smoking is a major determinant of bladder cancer, the lack of accurate information prevented researchers from determining how much of the risk was linked to smoking versus type 1 diabetes.

Lower Smoking Rates in Type 1 Diabetes

The Keck School team suspected that individuals with type 1 diabetes might smoke less frequently than the general public. Managing a serious lifelong condition may encourage healthier routines during adolescence and adulthood. If true, lower smoking rates could distort comparisons and obscure any diabetes-related risk.

To examine the idea, first author Helena Oskoui Bennett, MPH, then a student at the Keck School, collected smoking prevalence estimates from authoritative sources like the World Health Organization for populations included in the earlier studies.

Using a method known as meta-regression, the group identified patterns that supported their hypothesis and clarified why earlier analyses missed the association. After adjusting for smoking behavior, they calculated that people with type 1 diabetes were 4.29 times more likely to develop bladder cancer.

Diabetes Management and Cancer Prevention

The exact mechanism linking type 1 diabetes and bladder cancer remains uncertain, but researchers suspect the condition may induce biological changes that contribute to cancer formation.

Careful diabetes management, including maintaining stable blood sugar levels, may therefore help reduce bladder cancer risk. These biological changes may also interact with smoking in ways that heighten risk further.

“More work is needed to understand the mechanisms involved, but it is possible that there is a biological synergy between diabetes and smoking that increases risk more than either factor by itself,” Cortessis said.

This research grew out of a broader evaluation of type 2 diabetes, another condition associated with bladder cancer. The team is currently examining nearly one hundred studies on type 2 diabetes and various treatments to identify what contributes to the increased risk.

Reference:

1. Systematic review and meta-analysis corrected for history of smoking tobacco identifies type 1 diabetes as a possible risk factor for bladder cancer - (https://pubmed.ncbi.nlm.nih.gov/41173195/)

Source-Medindia