Probiotics for Preventing Upper Respiratory Tract Infections in Adults: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Table 1

Main characteristics of studies included in the meta-analysis.

Study author/year	Country	Study type	Participants	Age, years	No. of cases		Probiotics	Dose (CFU/d)	Administration form	Duration
					Probiotics	Placebo
Berggren et al., 2011 [20]	Sweden	RCT, double-blind	Healthy adults	18–65	159	159	L. plantarum HEAL9 and L. paracasei 8700 : 2	1 × 10^9	Powder	12 w
Murata et al., 2018 [23]	Japan	RCT, double-blind	Healthy females (most were students)	≥18	82	81	Heat-killed L. paracasei MCC1849	1 × 10^10	Powder	12 w
					78	—	Heat-killed L. paracasei MCC1849	3 × 10^10	Powder	12 w
Shida et al., 2017 [13]	Japan	RCT	Healthy males	30–49	50	50	L. casei Shirota LcS-FM	1 × 10^11	Milk	12 w
Langkamp-Henken et al., 2015 [22]	USA	RCT, double-blind	Healthy students	≥18	146	147	L. helveticus R0052	3 × 10^9	Capsule	6 w
					142	—	B. bifidum R0071	3 × 10^9	Capsule	6 w
					148	—	B. infantis R0033	3 × 10^9	Capsule	6 w
Hirose et al., 2013 [21]	Japan	RCT, double-blind	Healthy subjects with high mental pressure	40–64	39	39	Heat-killed L. plantarum L-137	NR	Tablet	12 w
Smith et al., 2013 [15]	USA	RCT, double-blind	Healthy students	18–25	114	117	B. animalis ssp. lactis BB-12 and L. rhamnosus LGG	>1 × 10^9	Powder	12 w

The number of participants in an intention-to-treat population (all the participants who were randomized to their original group, regardless of whether or not they completed the study). RCT: randomized controlled trial; NR: not reported.