Table 1. Main characteristics of studies pooled in this meta-analysis.
| Sample size | CRC incidents | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Author | Year | Ethnicity | Control source | Active | control | Age (year) | Male (%) | BMI (kg/m2) | Current smoker (%) | Prior disease (daily) | Folic acid | Additional treatment | Duration (months) | Active | control | Score of quality |
| Lonn et al.19 | 2006 | Mixed | HB | 2758 | 2764 | 68.9 | 71.8 | 29.7 | 11.5 | Vascular disease or diabetes | 2.5 mg | 50 mg vitamin B6 and 1 mg vitamin B12 | 60 | 50 | 37 | 5 |
| Cole et al.20 | 2007 | Mixed | HB | 516 | 505 | 57.0 | 63.8 | 27.5 | 14.5 | Colorectal adenoma | 1 mg | 81 mg or 325 mg aspirin or none | 75 | 3 | 4 | 5 |
| Logan et al.21 | 2008 | Caucasian | HB | 432 | 421 | NR | NR | NR | NR | Colorectal adenoma | 0.5 mg | 300 mg aspirin or none | 27 | 10 | 10 | 5 |
| Zhang et al.22 | 2008 | Caucasian | HB | 2721 | 2721 | 62.8 | 0 | 30.6 | 11.9 | CVD or 3 or more coronary risk factors | 2.5 mg | 50 mg vitamin B6 and 1 mg vitamin B12 | 88 | 18 | 22 | 3 |
| Wu et al.23 | 2009 | Caucasian | HB | 338 | 334 | 65.3 | 38.4 | 25.7 | 7.0 | Colorectal adenoma | 1 mg | None | 57 | 1 | 3 | 5 |
| Armitage et al.24 | 2010 | Caucasian | HB | 6033 | 6031 | 64.2 | 83.0 | NR | 12.0 | MI, other CHD, other vascular disease or diabetes | 2 mg | 1 mg vitamin B12 | 80 | 86 | 91 | 5 |
| Hankey et al.25 | 2012 | Mixed | HB | 4089 | 4075 | NR | 63.9 | NR | 23.3 | Stroke or transient ischemic attack | 2.5 mg | 50 mg vitamin B6 and 1 mg vitamin B12 | 41 | 21 | 21 | 5 |
| Gao et al.26 | 2013 | Asian | HB | 430 | 430 | 60.5 | 50.3 | NR | 17.3 | None | 1 mg | None | 36 | 2 | 2 | 4 |
HB, hospital based; BMI, body mass index; CVD, cardiovascular disease; MI, myocardial infarction; CHD, coronary heart disease; CRC, colorectal cancer; NR, not reported.