Table 3.
Risk of bias review of included studies
| Type of bias | Selection | Performance | Detection | Attrition | Reporting | Other bias | ||
|---|---|---|---|---|---|---|---|---|
| Study (author, year) | Random sequence generation | Allocation concealment | Blinding: participants and research personnel | Group comparability | Blinding: outcome assessors | Incomplete outcome data | Selective reporting | |
| Vitamins A and E | ||||||||
| Hemila, 2002 | Low | High | Low | Low | High | High | Unclear | Unclear |
| Hemila, 2004 | Low | High | Low | Low | Low | High | Unclear | Unclear |
| Vitamin D | ||||||||
| De Gruijl, 2012 | Low | Low | High | Low | Low | Low | Low | Unclear |
| Goodall, 2014 | Low | Low | Low | Low | Low | Low | Low | Low |
| Laaksi, 2010 | Low | Low | Low | Low | Low | High | Low | High |
| Li-Ng, 2009 | Low | Low | Low | Low | Low | Low | Low | High |
| Murdoch, 2012 | Low | Low | Low | Low | Low | Low | Low | Low |
| Rees, 2013 | Low | Low | Low | High | Low | Low | Unclear | High |
| Shimizu, 2018 | Low | Unclear | Unclear | Low | Low | Low | Low | High |
| Simpson, 2015 | Low | Low | Low | Low | Low | Unclear | Low | Unclear |
| Zinc | ||||||||
| Douglas, 1987 | Unclear | Low | Low | Low | Low | High | Unclear | High |
| Eby, 1984 | Unclear | Unclear | Unclear | Unclear | Low | High | Low | High |
| Godfrey, 1992 | Low | Low | Low | Low | Low | Low | Unclear | Unclear |
| Mossad, 1996 | Low | Low | Unclear | Unclear | Low | Low | Low | High |
| Petrus, 1998 | Unclear | Unclear | Unclear | Unclear | Low | Low | Unclear | High |
| Prasad, 2000 | Unclear | Unclear | Low | High | Low | Low | Low | Low |
| Prasad, 2008 | Unclear | Unclear | Low | Unclear | Low | Unclear | Low | Low |
| Turner, 2000 | Unclear | Unclear | Low | Low | Low | Unclear | Low | High |
| Veverka, 2000 | High | High | Low | Low | Low | Unclear | Unclear | High |
| Weismann, 1990 | Unclear | Unclear | Unclear | Low | Unclear | High | High | Unclear |