Table 1.
The basic characteristics of all included studies.
| First author | Year | Country | Study design | Age | Quality score | Participants | Cases (%) | Noncases (%) | Folate | Categories (μg/d) | RR (95% CI) |
| Chang et al | 2007 | United States | Cohort | <84 | 7 | 97,275 | 280 (0.29%) | 96995 (99.71%) | Total folate intake | >711 vs ≤272 | 0.81(0.49–1.32) |
| Harris et al | 2012 | United States | PBCC | 54 ± 12 | 8 | 3899 | 1910 (48.99%) | 1989 (51.01%) | Dietary folate intakeTotal folate intake | Q4 vs Q1Q4 vs. Q1 | 0.88(0.74–1.06)0.90(0.75–1.08) |
| Kelemen et al | 2004 | United States | Cohort | 55–69 | 7 | 27,205 | 147 (0.54%) | 27058 (99.46%) | Dietary folate intakeTotal folate intake | ≥347 vs <238≥541 vs<257 | 1.45(0.83–2.53)1.73(0.90–3.33) |
| Kushi et al | 1999 | United States | Cohort | 55–69 | 6 | 29,083 | 139 (0.48%) | 28944 (99.52%) | Total folate intake | >488.5 vs. <240.9 | 1.63(0.97–2.76) |
| Larsson et al. | 2004 | Sweden | Cohort | 38-76 | 7 | 61,084 | 266 (0.44%) | 60818 (99.56%) | Dietary folate intake | ≥204 vs. <155 | 0.67(0.43–1.04) |
| McCann et al | 2003 | United States | PBCC | 40–85 | 7 | 820 | 124 (15.12%) | 696 (84.88%) | Dietary folate intake | >425 vs <236 | 0.82(0.38–1.77) |
| Navarro Silvera et al | 2006 | Canada | Cohort | 40–59 | 8 | 49,613 | 264 (0.53%) | 49349 (99.47%) | Dietary folate intake | >357 vs <248 | 0.78(0.44–1.40) |
| Pelucchi et al | 2005 | Italy | HBCC | NA | 8 | 3442 | 1031 (29.95%) | 2411 (70.05%) | Dietary folate intake | Q5 vs Q1 | 0.98(0.67–1.44) |
| Salazar-Martinez et al | 2002 | Mexico | HBCC | 20–79 | 7 | 713 | 84 (11.78%) | 629 (88.22%) | Dietary folate intake | ≥322 vs ≤197 | 1.70(0.95–3.05) |
| Tworoger et al | 2006 | United States | Cohort | 30–55 | 8 | 80,254 | 481 (0.6%) | 79773 (99.4%) | Dietary folate intakeTotal folate intake | Q5 vs Q1Q5 vs Q1 | 0.76(0.52–1.12)1.13(0.83–1.53) |
| Webb et al | 2011 | Australia | PBCC | 18–79 | 8 | 2777 | 1363 (49.08%) | 1414 (50.92%) | Dietary folate intakeTotal folate intake | >366 vs <252>546 vs <334 | 1.0(0.8–1.24)1.05(0.84–1.30) |
| Zhang et al | 2012 | China | HBCC | 47.2 ± 7.5 | 8 | 433 | 215 (49.65%) | 218 (50.35%) | Dietary folate intake | >310 vs <200 | 0.54(0.32–0.94) |