Table 3 Rating of the certainty of evidence for clinical outcomes.

GRADE domain	Judgment	Concerns about certainty domains
Methodological limitations of the studies	Among the nine RCTs, the majority expressed ‘some concerns’ with respect to the risk of bias. Two studies were judged at low risk of bias and one study had a high risk of bias. The risk of bias of the remaining five intervention and observational studies was judged at low or moderate for two studies, and serious or critical for three studies. Main aspects that raise concerns were reporting participant-reported outcomes, incomplete or unclear reporting of methods or results, and small study populations. Therefore, we judged the studies to have serious methodological limitations.	Serious
Indirectness	Most studies were primarily aimed to investigate the effect of the dietary supplement on clinical outcomes, but often in combination with other treatments. We judged the evidence to have moderate indirectness.	Moderate
Imprecision	The total number of participants included in all studies was 819. We judged the evidence to have moderate imprecision.	Moderate
Inconsistency	The majority of the studies found a beneficial effect of the supplement intake on one or more of the clinical outcomes. There is inconsistency in the effects on different time points, but this could be addressed by variation in study protocol. We judged the evidence to have moderate inconsistency.	Moderate
Publication bias	Some studies are commercial studies. We found no commercial studies without effect.	Potential