Table 2.
Association between unmetabolized folic acid level (nmol/L) and the risk of total and subtypes of colorectal cancer*
| Endpoint | Unmetabolized folic acid, nmol/L | P trend | ||
|---|---|---|---|---|
| Undetectable | <0.5 | ≥0.5 | ||
| Median, nmol/L | 0 | 0.10 | 0.53 | |
| Colorectal cancer | ||||
| No. of case patients/control | 254/437 | 233/507 | 131/263 | |
| Crude OR† (95% CI) | 1.00 | 0.94 (0.67 to 1.31) | 1.01 (0.74 to 1.38) | .71 |
| Multivariable† OR (95% CI) | 1.00 | 1.03 (0.73 to 1.46) | 1.12 (0.81 to 1.55) | .32 |
| Colon cancer | ||||
| No. of case patients | 152 | 147 | 78 | |
| Crude OR (95% CI) | 1.00 | 1.10 (0.75 to 1.59) | 0.81 (0.55 to 1.19) | .25 |
| Multivariable† OR (95% CI) | 1.00 | 1.20 (0.82 to 1.77) | 0.90 (0.61 to 1.34) | .75 |
| Proximal colon cancer | ||||
| No. of case patients | 96 | 83 | 55 | |
| Crude OR (95% CI) | 1.00 | 1.27 (0.82 to 1.96) | 0.99(0.64 to 1.54) | .89 |
| Multivariable† OR (95% CI) | 1.00 | 1.39(0.89 to 2.19) | 1.16 (0.73 to 1.85) | .39 |
| Distal colon cancer | ||||
| No. of case patients | 55 | 63 | 22 | |
| Crude OR (95% CI) | 1.00 | 0.79 (0.42 to 1.48) | 0.55(0.28 to 1.08) | .08 |
| Multivariable† OR (95% CI) | 1.00 | 0.86 (0.45 to 1.62) | 0.56 (0.28 to 1.11) | .11 |
| Rectal cancer | ||||
| No. of case patients | 45 | 46 | 21 | |
| Crude OR (95% CI) | 1.00 | 0.68 (0.32 to 1.45) | 0.94 (0.51 to 1.72) | .08 |
| Multivariable† OR (95% CI) | 1.00 | 0.82 (0.38 to 1.77) | 1.10 (0.58 to 2.08) | .63 |
* Conditional logistic regression was utilized for colorectal cancer, and unconditional logistic regression was used for the subsites of large bowel. Tests for trend were performed by assigning the median (loge-transformed plasma levels) of each category of unmetabolized folic acid as a continuous variable in the models. All statistical tests were two-sided, and a P value of less than .05 was considered statistically significant. CI = confidence interval; OR = odds ratio.
† Multivariable models are adjusted for age at blood draw (continuous), date of blood draw (continuous), sex (male, female), race (white vs nonwhite), height (continuous), fasting status (yes, no), pack-years of smoking (continuous), body mass index (continuous), physical activity (in quartiles), family history of colorectal cancer (yes or no), history of colonoscopy or sigmoidoscopy (yes or no), alcohol intake (continuous), intake of red and processed meat (in quartiles), vitamin D intake (continuous), calcium intake (continuous), and aspirin use (nonusers vs ever users).