Table 3.

GRADE assessment of the certainty of evidence regarding the effect of vitamin D supplementation on inflammatory and oxidative stress markers

Biomarker	No of interventions	Risk of bias1	Inconsistency (heterogeneity)2	Indirectness3	Imprecision4	Publication bias 5	Effect size6	Certainty of evidence
25(OH)D	15	Very serious	Very serious	Serious	Not serious	Serious	+ 2	Low
CB 25(OH)D	3	Very serious	Very serious	Serious	Very serious	Very serious	+ 2	Very low
hs-CRP	11	Very serious	Very serious	Serious	Serious	Not serious	0	Very low
TAC	9	Very serious	Very serious	Serious	Not serious	Serious	+ 2	Low
MDA	6	Very serious	Serious	Serious	Not serious	Serious	0	Low
GSH	9	Very serious	Very serious	Serious	Not serious	Serious	+ 2	Low

1 risk of bias: no problem = not serious (0); problem with 1 element = severe (-1); problem with 2 or more elements = very severe (-2)

2 inconsistency: I2 < 50% = not serious (0), 50–75% = serious (-1), > 75% = very serious (-2)

3 indirectness or variation in participants, intervention, outcome variables: no problem = low; problem with 1 element = serious (-1); problem with 2 or more elements = very serious (-2)

4 imprecision: > 5 studies = not serious (0); 4 to 5 studies = serious (-1); 3 or less studies = very serious (-2)

5 publication bias: no publication bias = not serious, publication bias proved by only one method of assessment = serious, publication proved by more than one method of assessment besides a considerable difference between the combined and pure measurement = very serious

6 scoring: lower than 0.5 = 0, between 0.5 and 0.79 =  + 1, 0.8 or higher =  + 2

Abbreviations: 25(OH)D 25-​hydroxyvitamin D3, CB Cord Blood, hs-CRP High-sensitivity C-reactive protein, K Number of studies, TAC Total antioxidant capacity, MDA Malondialdehyde, GSH Glutathione