Summary of evidence on associations between intake of folic acid and risk of CRC: Studies are level II evidence.
| STUDY | DETAILS OF STUDY | RESULTS |
|---|---|---|
| Benito et al,26 1991 | Case-control study: 286 cases of CRC compared with 295 population controls and 203 hospitalized controls | Both legume fibre and folic acid had a protective effect |
| Ferraroni et al,27 1994 | Case-control study: 828 colon cancer cases and 498 rectal cancer cases compared with 2024 hospitalized controls | RR 0.52; inverse association found for both colon and rectal cancer across sex and age |
| Bird et al,28 1995 | Case-control study: 332 cases compared with 350 controls | Significant association between adenomatous polyps and red-cell folate levels (OR 0.76, 95% CI 0.53–1.08 for highest level vs lowest level); plasma folate levels and folate intake had similar but weaker associations with occurrence of polyps |
| Kato et al,29 1999 | Nested case-control study: 105 cases of CRC compared with 523 controls | OR 1.99 (95% CI 0.92–4.29) for patients with low serum folate levels and high alcohol consumption |
| Giovannucci et al,30 1993 | Nurses’ Health Study, Health Professionals Study (prospective cohorts) | Increased risk of CRC with > 2 alcoholic drinks per day (RR 1.84, 95% CI 1.19–2.86 in women; RR 1.64, 95% CI 0.92–2.93 in men) |
| Giovannucci et al,31 1998 | Prospective cohort study of 88 756 subjects | After 15 years of multivitamin use, women with folic acid intake > 400 μg/d had a significantly reduced risk of CRC (RR 0.25, 95% CI 0.13–0.51) |
| Jacobs et al,32 2003 | Cancer Prevention Study II Nutrition Cohort study of 145 260 men and women | Regular (≥ 4 times/wk) use of multivitamins 10 y before enrolment was associated with reduced risk of CRC (rate ratio 0.71, 95% CI 0.57–0.89) |
| Platz et al,33 2000 | Health Professionals Follow-Up Study of 47 927 men | 71% of CRC cases in the population were attributable to 6 risk factors: obesity, physical activity, red meat consumption, alcohol use, smoking, and low folic acid levels |
CRC—colorectal cancer, CI—confidence interval, OR—odds ratio, RR—relative risk.