| | Study | Country | Year | Study design | Population of controls | Recruitment period | Cancer | Gender | Number of quantiles | Dietary folate (mcg/day) | Total folate (mcg/day) | Adjustments |
| | Chen et al. [90] | USA | 1996 | Nested case control | Healthy persons | 1986–1994 | CRC | Men | 3 | <317 versus >461 | | Adjusted for age, family history, and intake of folate, methionine, and alcohol |
| | Slattery et al. [91] | USA | 1999 | Matched case control | Healthy persons | 1991–1994 | Colon | Both | 3 | <126 versus >197
per 1000 kcals | | Adjusted for age, BMI, physical activity, energy intake, dietary fiber, and smoking |
| | Le Marchand et al. [23] | USA | 2002 | Matched case control | Healthy persons | 1994–1998 | CRC | Both | 3 | <278 versus >372 | <336 versus >1583 | Adjusted for age, gender, ethnicity, pack years of cigarette smoking, lifetime recreational physical activity, lifetime aspirin use, BMI 5 years ago, years of schooling, and intakes of nonstarch polysaccharides from vegetables and calcium from foods and supplements |
| | Jiang et al. [42] | China | 2005 | Nested case control | Healthy persons | 1989-1990 | Colon
rectal | Both | 4 | <115.6 versus >172
per 1000 kcals | | Adjusted for sex, age, methionine, smoking status drinking status, and zinc |
| | Le Marchand et al. [46] | USA (Hawaii and California) | 2005 | Nested case control | Healthy persons | 1993–1996 | CRC | Both | 3 | <253 versus >412 | <322 versus >590 | Adjusted for age, gender, and ethnicity |
| | Otani et al. [45] | Japan | 2005 | Matched case control | Hospital patients | 1998–2002 | CRC | Both | 3 | <343 versus >485 | | Matching factors and adjusted for smoking, alcohol consumption, BMI, and total dietary fiber intake |
| | Lightfoot et al. [58] | United Kingdom | 2008 | Matched case control | Hospital patients | 1997–2000 | CRC | Both | 3 | | <267 versus >397 | Adjusted for gender, and age |
| | Sharp et al. [60] | United Kingdom | 2008 | Matched case control | Healthy persons | 1998–2000 | CRC | Both | 4 | | <263.9 versus >348.6 | Adjusted for age, gender and total energy intake. |
| | Guerreiro et al. [31] | Portugal | 2008 | Case control | Healthy persons | Not reported | CRC | Both | 2 |
≤406.7> | | Adjusted for age, gender and CRC history |
| | Haghighi et al. [22] | Iran | 2009 | Case control | Hospital patients | 2004–2007 | CRC | Both | 2 |
≤320> |
≤450> | Not reported |
|
|
