Bladder cancer (BC) is common in high-income countries. Smoking is the most important risk factor, accounting for about half of the incident cases among men living in Europe. Other environmental risk factors include schistosomiasis, external beam radiation and a wide range of occupational exposures. BC risk also has a genetic component and genetic analysis has found 15 location in human DNA that affect risk.
Studies on BC risk and metabolic factors are rare and have shown inconsistent results. The inconsistencies may be due to analysis of men and women, muscle invasive (MIBC) and non-muscle invasive tumors (NMIBC) jointly and inadequate adjustment of smoking, a potentially strong confounder. The main aim of the study was to investigate sex-specific associations between body mass index (BMI), blood pressure (BP), glucose, triglycerides and cholesterol and risk of MIBC and NMIBC separately and combined. Furthermore, we investigated interaction between smoking and metabolic factors in relation to BC.
In a study comprising of about 800,000 men and women from 6 European cohorts and using survival analysis to investigate associations, we found that elevated levels BP and triglycerides were associated with increased risk of overall BC among men. Among women, elevated levels of BMI appeared to have a protective effect against risk of overall BC. Among men, elevated levels of BMI, triglycerides and cholesterol were associated with increased risk of NMIBC, while increased levels of BP were associated with increased risk of MIBC. Elevated levels of glucose were associated with increased risk of MIBC among women. We found no interaction between metabolic factors and smoking in relation to BC.
Our findings support an involvement of metabolic abnormalities in the risk of BC. While some associations differed in certain sub-groups, in general, there were no significant differences by smoking status and tumor sub-type. To further build up on our findings, future studies need to appropriately account the low BC incidence among women and never smokers and use more specific measures of metabolic factors.
The full study can be found at International Journal of Cancer.