Effects of collagen-based supplements on skin’s hydration and elasticity: A systematic review and meta-analysis

Systematic review

The geographic spread and steady publication of studies from 2014 to 2021 reflect an increasing international focus on oral collagen supplementation and its potential impact on skin aging.

Oral collagen supplements and skin hydration

Four studies (Yoon et al., Kim et al., Bolke et al., and Tak et al.) using the Corneometer CM825 (Courage-Khazaka, Cologne, Germany) consistently showed a significant increase in skin hydration [Table 6].^7,9,14,15 Hydrolysed collagen enhances hydration due to its moisture-retaining properties.¹⁴ Gly-Pro-Hyp peptide levels peak in the bloodstream 1–2 hours post-consumption, stimulating dermal fibroblast migration and growth.⁷ While the exact mechanism remains unclear, Asserin et al. suggested fibroblasts recognise Gly-Pro-Hyp, triggering collagen, elastin, and HA synthesis in the epidermis and dermis, improving hydration and elasticity.^7,14,16 This mechanism is supported by Tak et al., Cerbo et al., and Asserin et al.^15–17 Additionally, a clinical study detected Pro-Hyp in urine after collagen ingestion, confirming its stability and ability to reach skin tissue.¹⁵

The increase in skin hydration may also be due to the structural similarity between hydrolysed bovine collagen and human collagen. Bovine collagen shares 31% similarity with type I collagen alpha chain I, 18% with type I collagen alpha chain II, and 13% with type III collagen alpha chain I.⁹ Among collagen sources, bovine collagen exhibits the highest similarity to human collagen.⁹ Schwartz et al. attributed increased hydration partly to higher water intake from supplements and placebos.¹⁸ Tak et al. suggested that seasonal changes from winter to summer (February–June) during Kim et al.’s study may have influenced hydration and elasticity levels.^7,15

However, Zmitek et al. found no significant changes in skin hydration after 12 weeks, as measured by the DermaLab Series, SkinLab Combo hydration probe (Cortex Technology Aps, Hadsund, Denmark).¹⁹ This contrasts with other studies showing increased hydration. The decline observed in Zmitek et al.’s study is likely due to seasonal changes, transitioning from late autumn to winter.¹⁹ Low humidity, combined with colder outdoor temperatures and indoor heating, may have negatively impacted skin hydration.¹⁹

Oral collagen supplements and skin elasticity

Three studies (Yoon et al., Bolke et al., and Schwartz et al.) using the Cutometer MPA580 (Courage-Khazaka, Cologne, Germany) consistently reported a significant increase in skin elasticity [Table 7].^9,14,18 This improvement is attributed to molecular changes in the dermis’s extracellular matrix.¹⁴ Yoon et al. and Kim et al. suggested that hydrolysed collagen enhances elasticity by promoting elastin fibre synthesis and inhibiting MMP-2 and MMP-9, enzymes that degrade elastin.^7,14 MMP levels significantly impact elastin and, consequently, skin elasticity.⁷ Additionally, skin hydration plays a crucial role, as elastin conformation changes only occur in the presence of hydrated proteins.⁷ These findings align with Kim et al.’s conclusions, further supporting the increase in skin elasticity.⁷

Studies by Inoue et al. and Czajka et al. also reported increased skin elasticity.^20,21 In older subjects, improvements appeared more gradually, with noticeable effects emerging after 60 days of supplementation, unlike younger participants. Inoue et al. suggested that age-related changes in nutrient absorption may influence skin elasticity in the elderly.²⁰ Notably, among all reviewed studies, only Tak et al. addressed the impact of weather conditions on skin measurements.¹⁵ However, despite efforts to control this variable, complete regulation was not achieved.

In contrast, Cerbo et al., Zmitek et al., and Tak et al. reported a decrease in skin elasticity.^15,17,19 Zmitek et al. attributed this decline to seasonal changes from late autumn to winter, which likely impacted skin elasticity.¹⁹ Tak et al. shared a similar view, suggesting that the transition from winter to autumn contributed to reduced elasticity.¹⁵ Weather conditions were considered a potential influencing factor affecting study outcomes.

Collagen supplement dosage

Collagen doses ranged from 246 mg to 10,000 mg per day [Table 5]. While doses below 1,000 mg were used in two studies, the most common dose was 4,000 mg, with an average of 3,500 mg.^17,18 However, dosage alone was not a reliable predictor of effectiveness. Notably, three studies using 4,000 mg reported decreased hydration and elasticity, while others using the same dose observed improvements.^15,19,21 These discrepancies may be attributed to factors such as study duration or environmental conditions.

Collagen supplement side effects

Of the included studies, nine (Yoon et al., Bolke et al., Tak et al., Zmitek et al., Inoue et al., Schwartz et al., Kim et al., Asserin et al., Czajka et al.) reported no side effects.^{7,9,14–16,18-21} All found collagen supplements to be safe, with no adverse effects observed during the study period.

Meta-analysis

Heterogeneity significantly impacted skin hydration and elasticity outcomes in this meta-analysis. Initially, all relevant studies were included, resulting in high heterogeneity: I² = 99.8% for hydration [Figure 2] and I² = 82.4% for elasticity [Figure 3], likely due to variations in study design, interventions, and participant characteristics. Due to this, pooled effect sizes were unreliable. To reduce heterogeneity, we selected methodologically sound studies with the least variability. For hydration, we included Yoon et al. (2014), Asserin et al. (2015), Kim et al. (2018), and Bolke et al. (2019), reducing I² to 55.5% [Figure 4].^7,9,14,16 For elasticity, we included Inoue et al. (2016), Kim et al. (2018), and Bolke et al. (2019), lowering I² to 56.5% [Figure 5].^7,9,20 This approach ensured consistent and interpretable pooled results while maintaining the overall effect of collagen supplementation. To check for potential publication bias, funnel plots for hydration [Figure 6] and elasticity [Figure 7] were also created.

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Figure 2:

Forest plot of skin hydration (all studies).

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Figure 3:

Forest plot of skin elasticity (all studies).

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Figure 4:

Forest plot of skin hydration (selected studies).

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Figure 5:

Forest plot of skin elasticity (selected studies).

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Figure 6:

Funnel plot of skin hydration (all studies). The funnel plot appeared asymmetrical, with only two studies inside the funnel. This may suggest possible publication bias or study differences, but interpretation is limited due to the small number of included studies.

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Figure 7:

Funnel plot of skin elasticity (all studies).

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Effect of oral collagen supplements on elasticity during ageing

The studies included in the meta-analysis were Inoue et al. (2016), Kim et al. (2018), and Bolke et al. (2019), all of which demonstrated a positive effect on skin elasticity following intervention [Figure 5].^7,9,20 The pooled SMD for elasticity studies was 0.61 (CI: 0.21−1.02), suggesting a moderate effect. The prediction interval (PI) was 0.61 (-0.12−1.34), indicating that the effect size in future studies may vary within this range and the CI reflects the precision of the average effect estimate. Individual study results included an SMD of 0.238 for Inoue et al. (LCP), 0.578 for Inoue et al. (HCP), 0.452 for Kim et al., and 1.176 for Bolke et al., highlighting the intervention’s consistent positive impact on skin elasticity.^7,9,20

Sensitivity analysis was performed for both hydration and elasticity studies. For hydration, the pooled SMDs after excluding each study were: Yoon et al. (2014) 1.2714, Asserin et al. (2015) 1.1496, Kim et al. (2018) 1.4627, and Bolke et al. (2019) 1.1748.^7,9,14,16 For elasticity, the values were: Inoue et al. (2016) 0.7389 (L-CP), Inoue et al. (2016) 0.6226 (H-CP), Kim et al. (2018) 0.6640, and Bolke et al. (2019) 0.4124.^7,9,20 The consistent pooled effects suggest that the findings are robust and not driven by any single study.

Funnel plots for all studies were created for hydration [Figure 6] and elasticity [Figure 7] analyses. The Egger test for hydration studies showed significant asymmetry (z = 6.160, p < .001), suggesting potential publication bias. However, the bias correction (b = -0.059) was not significant (CI: -0.675, 0.556), indicating minimal impact on the meta-analysis results. In contrast, the Egger test for elasticity studies showed no asymmetry (z = -0.251, p = 0.802), with the bias correction (b = 0.778) also non-significant (CI: -1.220, 2.777), suggesting no publication bias.