Income dynamics and risk of colorectal cancer in individuals with type 2 diabetes: a nationwide population-based cohort study

Abstract

Abstract Evidence regarding the association between income and risk of colorectal cancer (CRC) is inconclusive. Furthermore, the relationship between income dynamics and CRC risk among individuals with type 2 diabetes (T2D) is unknown. Using nationally representative data from the Korean Health Insurance Service database, 1,672,811 adults with T2D aged 30 to 64 years and without a history of cancer were enrolled between 2009-2012. We determined income levels based on 20 quantiles of monthly health insurance premiums and assessed income quartiles annually for five years preceding participant enrollment. Hazard ratios(HRs) and 95% confidence intervals(CIs) were estimated after adjusting for sociodemographic factors, CRC risk factors, and diabetes duration and treatment. During follow-up (median, 7.8 years), 22,149 CRC cases developed at least 1 year after enrollment. Individuals with sustained low income (i.e., lowest income quartile) over five years had increased CRC risk (HR 1.11, 95% CI 1.05-1.18). In contrast, those with sustained high income (i.e., highest income quartile) had decreased CRC risk (HR 0.81, 95% CI 0.73-0.89), which was more pronounced for rectal cancer (HR 0.64, 95% CI 0.52-0.78) and distal colon cancer (HR 0.70, 95% CI 0.57-0.86). Income declines (i.e., a decrease≥25% in income quantile) were associated with increased CRC risk (HR≥2 vs. 0 declines 1.10, 95% CI 1.05-1.16; p trend=0.0007). Among those with low income at 5 years pre-enrollment, CRC risk decreased linearly with increasing income levels over five years(p trend<0.0001). Our findings highlight the need to better understand the mechanisms by which income dynamics impact CRC risk among individuals with T2D.