Effect of vitamin D status and vitamin D supplementation on immune function and prevention of acute respiratory tract infections in dark-skinned individuals: a systematic review and meta-analysis.

Objective: This systematic review and meta-analysis examined the evidence for a potential relationship between vitamin D status and vitamin D supplementation on immune function biomarkers and prevention of acute respiratory tract infections (ARTI) in dark-skinned individuals.

Design: Six databases were searched (inception to December 2021) for randomised controlled trials (RCT) and observational studies. A narrative synthesis and random-effects meta-analysis were used to synthesise the findings.

Setting: Not applicable.

Participants: Ethnic groups other than white, with or without a white comparator.

Results: After duplicates were removed, 2077 articles were identified for screening. A total of eighteen studies ( 36 707), including seven RCT and 11 observational studies, met the inclusion criteria, and three RCT ( 5778) provided sufficient data of high enough quality to be included in a meta-analysis. An inverse association between vitamin D status and at least one inflammatory biomarker in black adults was found in three studies, and vitamin D status was inversely associated with ARTI incidence in black and Indigenous groups in two studies. There was no significant effect of vitamin D supplementation on differences in ARTI incidence in ethnic minority groups (OR, 1·40; 95 % CI: 0·70, 2·79; = 0·34), nor African American (OR, 1·77; 95 % CI: 0·51, 6·19; = 0·37) or Asian/Pacific (OR, 1·08; 95 % CI: 0·77, 2·68; = 0·66) subgroups.

Conclusions: There is a lack of conclusive evidence supporting an association between vitamin D status and immune function or ARTI incidence in dark-skinned individuals. Further RCT in diverse ethnic populations are urgently needed.