Table 1. Important details of the studies included in this systematic review.

DCSS: diffuse cutaneous systemic sclerosis. MRSS: modified Rodnan skin thickness score. CP: collagen peptide. TEWL: trans-epidermal water loss. BCP: bioactive collagen peptide. LMWCP: low molecular weight collagen peptide. H-CP: higher collagen peptide. L-CP: lower collagen peptide

Details of Authors	Details about Subjects (n)	Details of Groups of study subjects	Details about origin of collagen, form of collagen and dose of collagen	Duration of study	Analysis of Results	Variables analysed
Postlethwaite and associates in year 2008 in population of USA [13]	DCSS patients (n = 168)	Intervention: type I collagen (n = 83) Placebo: acetic acid (n = 83)	Bovine/intact/500 µg per day	12 months	Decrease in late-phase DCSS compared with placebo	MRSS
Choi and associates in year; 2014 in population of the South Korea [25]	Healthy subjects	Group A: no supplement (n = 8) Group B: CP (n = 8) Group C: CP + vitamin C (n = 8) Group D: vitamin C (n = 8)	Hydrolysate/CP = 3 g and vitamin C = 500 µg	12 weeks	Increase in CP group compared with controls	Stratum corneum hydration
					Decrease in CP group compared with controls	TEWL
					Increase in CP group compared with controls	Skin elasticity
Kuwaba and associates in year 2014  [26]	Women with dry and saggy face	Intervention: CP/Placebo:	Fish/hydrolysate/5 g	8 weeks	Decreased compared with placebo group	Wrinkle number
					Increased compared with placebo group	Skin dryness
Proksch and associates in year 2014 in population of  Brazil  [2]	Healthy females (n = 57)	Intervention: BCP  Placebo: maltodextrin	NR/hydrolysate/2.5 g per day	8 weeks	Decreased compared with placebo group	Skin wrinkle volume
					Increased compared with placebo group	BCP type I procollagen
					Increased compared with placebo group	BCP elastin
Inoue and associates in year 2015 in population of China [14]	Healthy females	Intervention 1: H-CP (n = 28) Intervention 2: L-CP (n = 29) Placebo: maltodextrin (n = 28)	Fish gelatin/hydrolysate/5 g	8 weeks	Increase in H-CP group compared with L-CP and placebo; increase in L-CP group compared with placebo	Facial moisture
					Increase in H-CP group compared with L-CP and placebo.	Facial elasticity
					Decrease in H-CP group compared with L-CP and placebo; decrease in L-CP group compared with placebo	Facial roughness
Sugihara and associates in 2015 in population of  China [27]	Healthy females	Intervention: CP (n = 28) Placebo: maltodextrin (n = 28)	hydrolysate/2.5 g	8 weeks	Increased compared with placebo group	Facial hydration
					Increased compared with placebo group	Facial elasticity
					Decreased compared with placebo group	Facial roughness
Mori and associates in year 2017in population of Japan [12]	Healthy females with nail fragile and or thinly peeled off	Intervention: CP (n = 10) Placebo: dextrin (n = 10)	Porcine skin/hydrolysate/5 g	12 weeks	Increased compared with placebo group	Nail moisture
					Decreased compared with placebo group	Nail hardness
					Increased compared with placebo group	Nail sphingosine
					Increased compared with placebo group	Nail ceramides
Kim and associates in year 2018 in population of Korea [3]	Healthy females	Intervention: LMWCH (n = 32) Placebo: same formula except CP	Fish/hydrolysate/1 g	12 weeks	Increase in LMWCH group compared with Placebo	Skin hydration
					Decrease in LMWCH group compared with placebo	Crow's-feet scores
					Increase in LMWCH group compared with placebo	Skin elasticity
Koizumi and associates in year 2018 in population of Japan [15]	Healthy females	Intervention: beverage containing CP (n = 38) Placebo: beverage	Fish/hydrolysate/3 g	12 weeks	Increased compared with placebo group	Facial moisture
					Increased compared with placebo group	Skin elasticity
					Decreased compared with placebo group	Periorbital wrinkles
Yamamoto [28] and associates in year 2018 and population of Japan	Healthy subjects with dry skin	Intervention: drink containing CP (n = 18) Placebo: drink (n = 18)	Porcine skin/hydrolysate/10 g	8 weeks	Decreased compared with placebo group	TEWL