Mendelian randomisation analysis strongly implicates adiposity with risk of developing colorectal cancer

Background: Observational studies have associated adiposity with an increased risk of colorectal cancer (CRC). However, such studies do not establish a causal relationship. To minimise bias from confounding we performed a Mendelian randomisation (MR) analysis to examine the relationship between adiposity and CRC. Methods: We used SNPs associated with adult body mass index (BMI), waist-hip ratio (WHR), childhood obesity and birth weight as instrumental variables in a MR analysis of 9254 CRC cases and 18 386 controls. Results: In the MR analysis, the odds ratios (ORs) of CRC risk per unit increase in BMI, WHR and childhood obesity were 1.23 (95% CI: 1.02-1.49, P = 0.033), 1.59 (95% CI: 1.08-2.34, P = 0.019) and 1.07 (95% CI: 1.03-1.13, P = 0.018), respectively. There was no evidence for association between birth weight and CRC (OR = 1.22, 95% CI: 0.89-1.67, P = 0.22). Combining these data with a concurrent MR-based analysis for BMI and WHR with CRC risk (totalling to 18 190 cases, 27 617 controls) provided increased support, ORs for BMI and WHR were 1.26 (95% CI: 1.10-1.44, P = 7.7 x 10(-4)) and 1.40 (95% CI: 1.14-1.72, P = 1.2 x 10(-3)), respectively. Conclusions: These data provide further evidence for a strong causal relationship between adiposity and the risk of developing CRC highlighting the urgent need for prevention and treatment of adiposity.Peer reviewe