However, this metastudy concluded that due to the identified limitations of the included studies, larger, randomized trials are needed to confirm these findings.

Quality scores of included studies ranged from 45.5 to 82 out of a possible100.

Click here for file Additional file 2 Containing Table: clinical characteristics of patients enrolled in included studies.

In ten of the included studies (83%), a primary outcome was the change in antioxidant activity.

Of the included studies, three of the five community trials plus two of the three measles trials reported cause specific mortality.

However, many of the included studies received lower quality scores because they failed to describe the randomization procedure and participant withdrawals or drop-outs from the study.

Overall, 552 patients were enrolled in the included studies.

Additional file Table 1: Characteristics of included studies.

Risk of bias: Is a judgement made on the basis of the chance that bias in included studies have influenced the estimate of effect.

Inconsistency: Is a judgement made on the basis of the variability of results across the included studies.