Background:
Diabetes mellitus (DM) is a global health issue that varies substantially across socioeconomic groups and is becoming increasingly common in younger populations. However, the effects of DM on early-onset cancer (diagnosed before age 50) have not been investigated in the general population while taking socioeconomic disparities into account.
Methods:
In this prospective cohort study, all Finnish residents aged ≥18 years were followed for incident cancers diagnosed before age 50 from January 2010 to December 2021 through linkage with multiple national registries. Associations between DM and cancer risk were estimated using Cox regression models. Population attributable fractions (PAFs) for DM were estimated across socioeconomic groups.
Results:
A total of 1.3 million Finnish residents were included in the study, of whom 93,479 had diabetes mellitus at baseline. Individuals with diabetes had an elevated risk of overall cancer, although the associations differed across socioeconomic groups. Among individuals with low education (n = 179,508), 10.1% had diabetes and had a 36% higher risk of overall cancer (HR 1.36, 95% CI 1.25–1.48). Among those with medium education (n = 542,693), 8.4% had diabetes and had a 24% higher risk of overall cancer (HR 1.24, 95% CI 1.17–1.31). Among those with high education (n = 523,693), 5.7% had diabetes and had a 28% higher risk of overall cancer (HR 1.28, 95% CI 1.20–1.36).
Disparities in cancer risk attributable to diabetes were also observed across socioeconomic groups, with substantially higher PAFs among individuals with low education (low education: PAF 3.4%; high education: PAF 1.6%). The gradient was most evident for liver cancer (low education: PAF 20.6%; high education: PAF 13.9%), kidney cancer (low education: PAF 12.6%; high education: PAF 4.9%), corpus uteri cancer (low education: PAF 13.5%; high education: PAF 6.6%), and brain cancer (low education: PAF 9.5%; high education: PAF 3.6%). For pancreatic cancer, PAFs were slightly higher in the high-education group than in the low-education group (low education: PAF 15.5%; high education: PAF 18.4%).
Conclusions:
In this nationwide cohort study from Finland, DM was associated with an increased risk of early-onset cancer, and the resulting attributable cancer burden differed across socioeconomic groups. Higher PAFs among individuals with lower education suggest a disproportionate impact of diabetes on disadvantaged populations. Further investigations are needed to clarify how the age of diabetes onset may influence different histological types of early-onset cancers.