Table 1.

Characteristics of the anxiety/stress studies included in the systematic review.

Study	Intervention Type	Delivery Method	Active Compound	Dose	Frequency (Dose/Day)	Duration (Days)	Active/ Control	Mean Age	Sex (M/F)	Anxiety Measure	Effect WITHIN-AG	Effect BETWEEN-G	Stress Measure	Effect WITHIN-AG	Effect BETWEEN-G	Participants	Risk of Bias
Adikari et al., (2020) [55]	probiotic	liquid	Lactobacillus Casei Shirota	3 × 1010 CFU	1	56	10/9	19	19/0	-	-	-	EDR	-	ns	football players
													HR	-	ns
Capitao et al., (2020) [70]	prebiotic	sachet	B-GOS	-	1	84	17/18	8.84	24/11	STAIC	ns	ns	salivary cortisol	-	ns	children with below-average literacy skills
Chong et al., (2019) [56]	probiotics	sachet	Lactobacillus Plantarum DR7	1 × 109 CFU	1	84	27/32	24.8	-	DASS-42 anxiety	<	↓	PSS-10	<	ns	healthy young adults
													DASS-42 stress	<	↓
Culpepper et al. (2016) [57]	probiotic	capsule	Lactobacillus helveticus R0052	3 × 109 CFU	1	42	145	19.9	209/372	-	-	-	self-reported stress	-	↓ for B. Bifidum only, only in sleep deprived students	students e.s.
			Bifidobacterium longum ssp. infantis R0033				147
			Bifidobacterium bifidum R0071				142
			placebo				147
Hughes et al. (2011) [58]	prebiotic	sachet	GOS	0, 2500, 5000 mg	1	56	279/140	19.9	207/212	-	-	-	self-reported stress	-	ns	students e.s.
Karbownik et al. (2020) [59]	probiotic	capsule	Saccharomyces boulardii	5 × 109 CFU	1	30	31/29	22.6	37/55	STAI state	<	ns	salivary cortisol	+	ns	students e.s.
													salivary metanephrine	ns	ns
													pulse rate	+	↑
Kato-Kataoka et al. (2016) [60]	probiotic	liquid	Lactobacillus casei Shirota	100 × 109 CFU	1	56	23/24	22.8	25/22	STAI state	-	ns	visual analogue stress scale	-	↓	students e.s.
													salivary cortisol	-	↓
													salivary alpha-amylase	-	ns
Kato-Kataoka et al. (2016) [61]	probiotic	liquid	Lactobacillus casei Shirota	100 × 109 CFU	1	56	24/23	22.9	26/21	STAI state	-	ns	salivary cortisol	-	ns	students e.s.
													salivary immunoglobulin A	-	ns
Kitaoka et al. (2009) [62]	prebiotic	capsule	Fermented Ginseng	205 mg	9	8	8/8	20.7	16/0	STAI total	<	-	salivary cortisol	ns	-	healthy subjects
										POMS	ns	-	salivary immunoglobulin A	ns	-
Kelly et al. (2017) [63]	probiotic	capsule	Lactobacillus rhamnosus	1 × 109 CFU	1	28	15/14	24.6	29/0	BAI	ns	ns	PSS-10	ns	ns	healthy subjects, SECPT
										STAI trait	ns	ns	cortisol SECPT	-	ns
										STAI state	<	ns	self-reported stress SECPT	ns	ns
Kiecolt-Glaser et al. (2011) [64]	prebiotic	capsule	omega-3 PUFAs	2500 g	1	84	34/34	23.7	38/30	BAI	-	↓	-	-	-	students e.s.
Liu et al. (2019) [65]	probiotic	capsule	Lactobacillus plantarum PS128	30 × 109 CFU	ns	30	36/35	10.0	71/0	CBCL	-	ns	-	-	-	ASD children
Manos et al. (2018) [66]	prebiotic	capsule	omega-3-PUFAs	782 mg	4	84	10/8	14.7	0/18	BAIT	<	↑	-	-	-	anorexic girls
Marcos et al. (2004) [70]	probiotic	liquid	Lactobacillus delbrueckii bulgaricus	1 × 109 CFU	2	21	73/63	18–23	40/96	STAI state	+	ns	serum cortisol	-	ns	students e.s.
			Streptococcus salivarius thermophilus	10 × 109 CFU						STAI trait		ns
			Lactobacillus casei DN114001	10 × 109 CFU
Papalini et al. (2019) [67]	probiotic	powder	Bifidobacterium bifidum W23, Bifidobacterium lactis W51, Bifidobacterium lactis W52, Lactobacillus acidophilus W37, Lactobacillus brevis W63, Lactobacillus casei W56, Lactobacillus salivarius W24, Lactococcus lactis W19, Lactococcus lactis W58	2.5 × 109 CFU	2	28	29/29	21.5	0/58	-	-	-	VAS	+	ns	healthy subjects, SECPT
													cortisol	+	ns
													alpha-amylase	+	ns
													HR	+	ns
													BP	+	ns
Schmidt et al. (2015) [68]	prebiotic	powder	FOS	5500 mg	1	21	15	23.7	22/23	STAI state	-	ns	PSS-10	-	ns	healthy subjects
			B-GOS				15						salivary cortisol	-	↓ GOS only
			placebo				15
Tran et al. (2019) [69]	probiotic	-	18 species	50 × 109 CFU (condition A)	1	28	14	20.6	20/66	BAI	-	ns BAI total	-	-	-	healthy students
			10 species	50 × 109 CFU (condition B)			13					-
			18 species	15 × 109 CFU (condition D)			15			PSWQ		↓50 × 109 CFU only
			10 species	10 × 109 CFU (condition E)			15
			placebo				11

↓: Improvement vs. placebo; ↑: diminishment vs. placebo; <: decrease vs. baseline; +: increase vs. baseline; ns: no significant effect; -: not reported or not applicable; dose refers to amount of active compound. FOS: fructooligosaccharides; B-GOS: Bimuno^®-galactooligosaccharides; PUFAs: polyunsaturated fatty acids; EDR: electrodermal activity; HR: heart rate; DASS-42: Depression Anxiety Stress Scale 42; BP: blood pressure; BAI: Beck Anxiety Inventory; CBCL: Child Behavior Checklist (Anxiety); CFU: colony-forming unit; PASAT: Paced Auditory Serial Addition Test; PSS: Perceived Stress Scale-10; PSWQ: Penn State Worry Questionnaire; STAI: State-Trait Anxiety Inventory; STAIC: State-Trait Anxiety Inventory for Children; e.s.: under examination stress, VAS: visual analogue scale; PSS-10: perceived stress scale; SECPT: socially evaluated cold pressor test; POMS: profile of mood states; ASD: autism spectrum disorders.