Table 2.
Estimates of the effect of body mass index on risk of colorectal cancer (CRC), colon cancer and rectal cancer obtained using conventional covariate-adjusted and instrumental variable (IV) analysis (Odds ratios per 5 kg/m2)
| Conventional covariate-adjusted analysis |
Instrumental variable analysis |
||||
|---|---|---|---|---|---|
| Controls / Cases |
Minimally adjusted ORa (95% CI) |
Fully adjusted ORb (95% CI) |
IV-ORc (95% CI) |
Pd | |
| All | |||||
| CRC | 10286/10226 | 1.18 (1.15–1.22) | 1.17 (1.14–1.21) | 1.50 (1.13–2.01) | 0.10 |
| Colon cancer | 10286/6864 | 1.19 (1.15–1.23) | 1.18 (1.14–1.22) | 1.50 (1.08–2.07) | 0.17 |
| Rectal cancer | 10286/2365 | 1.15 (1.09–1.21) | 1.14 (1.08–1.20) | 1.26 (0.77–2.04) | 0.73 |
| Men | |||||
| CRC | 4539/4582 | 1.30 (1.23–1.38) | 1.29 (1.22–1.37) | 1.18 (0.73–1.92) | 0.70 |
| Colon cancer | 4539/2942 | 1.31 (1.23–1.39) | 1.29 (1.21–1.37) | 1.03 (0.60–1.78) | 0.39 |
| Rectal cancer | 4539/1253 | 1.25 (1.14–1.36) | 1.25 (1.13–1.37) | 1.33 (0.62–2.85) | 0.87 |
| Women | |||||
| CRC | 5747/5644 | 1.14 (1.10–1.18) | 1.12 (1.08–1.17) | 1.82 (1.26–2.61) | 0.01 |
| Colon cancer | 5747/3922 | 1.15 (1.10–1.20) | 1.13 (1.08–1.18) | 1.94 (1.30–2.91) | 0.01 |
| Rectal cancer | 5747/1112 | 1.11 (1.04–1.18) | 1.08 (1.01–1.16) | 1.24 (0.64–2.37) | 0.74 |
CI, confidence interval; OR, odds ratio.
Adjusted for age, sex, and study.
Adjusted 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.
Using 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.
For comparison of IV-OR with minimally adjusted OR (P<0.05 rejects the null hypothesis that they are equal).