Table 2.

Estimates of the effect of BMI on risk of colorectal cancer, colon cancer, and rectal cancer obtained using conventional covariate-adjusted and IV analysis (OR per 5 kg/m2)

Conventional covariate-adjusted analysisInstrumental variable analysis
Controls/casesMinimally adjusted ORa (95% CI)Fully adjusted ORb (95% CI)IV-ORc (95% CI)Pd
All
 CRC10,286/10,2261.18 (1.15–1.22)1.17 (1.14–1.21)1.50 (1.13–2.01)0.10
 Colon cancer10,286/6,8641.19 (1.15–1.23)1.18 (1.14–1.22)1.50 (1.08–2.07)0.17
 Rectal cancer10,286/2,3651.15 (1.09–1.21)1.14 (1.08–1.20)1.26 (0.77–2.04)0.73
Men
 CRC4,539/4,5821.30 (1.23–1.38)1.29 (1.22–1.37)1.18 (0.73–1.92)0.70
 Colon cancer4,539/2,9421.31 (1.23–1.39)1.29 (1.21–1.37)1.03 (0.60–1.78)0.39
 Rectal cancer4,539/1,2531.25 (1.14–1.36)1.25 (1.13–1.37)1.33 (0.62–2.85)0.87
Women
 CRC5,747/5,6441.14 (1.10–1.18)1.12 (1.08–1.17)1.82 (1.26–2.61)0.01
 Colon cancer5,747/3,9221.15 (1.10–1.20)1.13 (1.08–1.18)1.94 (1.30–2.91)0.01
 Rectal cancer5,747/1,1121.11 (1.04–1.18)1.08 (1.01–1.16)1.24 (0.64–2.37)0.74

Abbreviation: CRC, colorectal cancer.

  • aAdjusted for age, sex, and study.

  • bAdjusted for age, sex, study, smoking status, family history of cancer, aspirin/NSAID use, diabetes, fruit, vegetable, processed meat, red meat, and (women only) menopause hormone therapy.

  • cUsing weighted genetic risk score derived from 77 SNPs as an instrumental variable for BMI (Mendelian randomization), adjusted for study and the top three principal components of ancestry.

  • dFor comparison of IV-OR with minimally adjusted OR (P < 0.05 rejects the null hypothesis that they are equal).