The effect of low-dose aspirin on colorectal cancer prevention and gastrointestinal bleeding according to bodyweight and body mass index: Analysis of UK primary care data.

Background: Meta-analysis of trial data suggests that in primary cardiovascular disease (CVD) prevention bodyweight modifies low-dose aspirin's effects on colorectal cancer (CRC) and major bleeding risk. We sought to investigate whether these effects are seen in patients with or without CVD in routine clinical practice by undertaking sub-analyses of data from two cohort studies with nested-case-control analyses.

Methods: We followed ~200,000 new users of low-dose aspirin (75-300 mg/day) and a matched cohort of non-users to identify incident cases of CRC/upper gastrointestinal bleeding (UGIB). Adjusted relative risks (RRs) with 95% confidence intervals (CIs) were calculated for current vs. non-use of low-dose aspirin using logistic regression stratified by bodyweight/body mass index (BMI) strata.

Results: RRs (95% CIs) for CRC by bodyweight were: 0.60 (0.50-0.72) for ≤70 kg, 0.68 (0.60-0.76) for >70 kg; and by BMI were 0.60 (0.52-0.68) for ≤28 kg/m, 0.76 (0.64-0.89) for >28 kg/m. For UGIB, estimates were: 1.49 (1.28-1.74) for ≤90 kg, 1.78 (1.29-2.45) for >90 kg/m, 1.44 (1.21-1.72) for ≤28 kg/m, 1.72 (1.38-2.16) for >28 kg/m. Results were similar in the primary CVD prevention population.

Conclusion: Our findings suggest that the effects of low-dose aspirin in reducing CRC risk and increasing UGIB risk are not modified by bodyweight/BMI.