The role of smoking in bladder cancer risk: Unveiling racial and ethnic disparities in US and global populations, a secondary dataset analysis.

INTRODUCTION: Bladder cancer is a common malignancy of the urinary system, with smoking recognized as its most significant modifiable risk factor. Although substantial epidemiological evidence has established an association between smoking and bladder cancer, there remains a gap in understanding the complex burden and risk patterns of bladder cancer across different populations. This study aims to investigate the potential relationship between smoking and bladder cancer risk among individuals aged ≥20 years by leveraging large-scale, multinational data. METHODS: This cross-sectional study utilized two databases: the Global Burden of Disease (GBD) 2021 and the National Health and Nutrition Examination Survey (NHANES) cross-sectional data cycles from 1999 to 2023. After excluding participants with missing data on smoking history, bladder cancer history, and other relevant variables, individuals aged ≥20 years were included. The GBD data provided macro-level estimates of bladder cancer mortality and disability-adjusted life years (DALYs) attributable to smoking both globally and within the United States. Individual-level data from NHANES were used to assess the association between smoking history and bladder cancer risk through multivariable logistic regression models, adjusting for multiple confounding factors. RESULTS: Smoking is a major risk factor for bladder cancer both globally and in the US, with the smoking-attributable burden of bladder cancer markedly higher in the US. In 2021, the age-standardized death rate (ASDR) in the US was 1.97 (95% uncertainty interval, UI: 1.57-2.47), significantly exceeding the global rate of 1.12 (95% UI: 0.94-1.35). Similarly, the US age-standardized disability-adjusted life year rate (ASDAR) was substantially higher than the global average, at 42.60 (95% UI: 34.89-51.57) versus 23.56 (95% UI: 19.87-28.13). From the NHANES study, a total of 66391 participants were included, among whom 187 had bladder cancer. The data demonstrated a significant positive association between smoking and bladder cancer risk; compared to never smokers, smokers had an adjusted odds ratio (AOR) of 2.00 (95% CI: 1.31-3.07), indicating a two-fold increased risk of bladder cancer. Further sensitivity analyses suggested that former smokers were associated with a 70% higher likelihood of risk, while current smokers showed a 265% higher likelihood. Additionally, subgroup analyses indicated differences in the observed risk across various racial groups. CONCLUSIONS: This study elucidates a significant positive association between smoking and bladder cancer risk among individuals aged ≥20 years, with notable racial/ethnic disparities observed. Our findings suggest the need for further investigation into strategies that may address these disparities. However, the cross-sectional design limits causal inference. Future longitudinal studies are warranted to investigate the carcinogenic effects of emerging tobacco products, particularly across different racial groups, to optimize prevention and control measures.