The Effects of Prebiotics, Synbiotics and Short-Chain Fatty Acids On Respiratory Tract Infections and Immune Function: A Systematic Review And Meta-Analysis.

Prebiotics, synbiotics and short-chain fatty acids (SCFA) have been shown to decrease systemic inflammation and play a protective role in chronic respiratory conditions. However, the effect on infection and immune function are unclear. The objective of this systematic review was to summarise the current evidence for prebiotic, synbiotic and SCFA supplementation on respiratory tract infections (RTIs) and immune function. Relevant English language articles up to May 2021 were identified via online databases: MEDLINE, EMBASE, CINAHL, and Cochrane Library. Included studies (n = 58) examined the effect of prebiotics, synbiotics or SCFA, delivered orally, on the incidence, severity or duration of RTIs and/or markers of immune function (e.g. peripheral blood immunophenotyping, NK cell activity). The majority of studies were randomized controlled trials (RCTs) reporting on RTIs in infants and children. Meta-analysis indicated that the number of subjects with ≥1 RTI were reduced with prebiotic (OR 0.73, 95% CI [0.62, 0.86], P = 0.0002, n = 17) and synbiotic (OR 0.75, 95% CI [0.65, 0.87], P = 0.0001, n = 9) supplementation compared to placebo. Further, NK cell activity was increased with synbiotic (SMD 0.74, 95% CI [0.42, 1.06], P < 0.0001, n = 3) supplementation. This review provides evidence that prebiotic, specifically oligosaccharide, supplementation may play a protective role in RTIs in infants and children. There is less evidence for this effect in adults. Supplementation with pre- and synbiotic treatment may alter immune function by increasing NK cell activity, though effects on immunophenotype were less clear.