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BACKGROUND: Previous studies have shown a positive association between type 2 diabetes (T2D) and colorectal cancer (CRC) risk. However, it is uncertain whether this association differs by duration of T2D or sex. We thus investigated the associations of T2D and its duration with the risk of incident CRC.

METHODS: We followed 87,523 women from the Nurses' Health Study (1980-2012) and 47,240 men from the Health Professionals Follow-up Study (1986-2012). Data on physician-diagnosed T2D was collected at baseline with a questionnaire and updated biennially. Cox regression models were used to estimate multivariable-adjusted hazard ratios (HRs) and 95% confidence intervals (CIs).

RESULTS: We documented 3000 CRC cases during up to 32 years of follow-up. Among men, T2D was associated with increased risk of CRC compared to those without T2D (HR: 1.42; 95% CI: 1.12-1.81). This positive association persisted in sensitivity analyses by excluding CRC identified within 1 year of diabetes diagnosis and patients with T2D who used hypoglycaemic medications. Among women, T2D was positively, but not statistically significantly, associated with CRC risk (HR: 1.17; 95% CI: 0.98-1.39).

CONCLUSIONS: Our findings support that T2D was associated with a moderately higher risk of developing CRC in men; a weaker, nonsignificant positive association was observed in women.