Collagen · The Ingredient Files

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Evidence by effect

Evidence strength (A–D, color) and effect size (dots, fill) are shown separately. The two axes are independent.

Claimed effect

Evidence strength

Effect size

One-line summary · key source

Improving skin elasticity, hydration, and wrinklesEvidence type: Meta-analysis

B Moderate

Moderate

Collagen's best-supported use. A meta-analysisA statistical synthesis combining results of multiple studies into one conclusion. of 19 hydrolyzed-collagen RCTRandomized controlled trial - a high-reliability trial that randomly assigns participants to compare effects.s (1,125 people, 95% women) found skin hydration, elasticity, and wrinkles improved versus placeboAn inert dummy treatment used as the comparison baseline., with hydration and elasticity confirmed in subgroup analysis (generally at 90 days). Individual double-blind RCTs likewise showed 2.5 to 5 g/day of collagen peptides significantly raising skin elasticity at 8 weeks. However, the measures are instrument-read surrogate endpointAn intermediate measure (e.g., skin elasticity readings, bone density) used in place of a final outcome; it does not always track real clinical benefit.s (elasticity and hydration readings), the trials are mostly in women and short-term, and some involved manufacturing or research institutes. PMID: 33742704 · 23949208

Easing osteoarthritisThe most common degenerative joint disease, in which cartilage wears down causing pain and stiffness (OA). symptomsEvidence type: Meta-analysis

C Weak

Minimal

In joints the results are mixed. A meta-analysisA statistical synthesis combining results of multiple studies into one conclusion. of placeboAn inert dummy treatment used as the comparison baseline.-controlled RCTRandomized controlled trial - a high-reliability trial that randomly assigns participants to compare effects.s found collagen lowered the total WOMACA standard index scoring pain, stiffness, and function in knee or hip osteoarthritis. index (mean difference -8.00, P=0.002) and the pain visual scale (VAS -16.57, P<0.001). But breaking down the subscores, stiffness fell (P=0.01) while the pain (P=0.75) and functional-limitation (P=0.81) subscores were not statistically significant. So the composite scores improved but the core gains in pain and function were not consistently confirmed, leaving weak grounds to say it clearly works for joints. PMID: 30368550

Increasing bone mineral densityA measure of the mineral content of bone; lower values indicate weaker bones. in postmenopausal womenEvidence type: RCTRandomized controlled trial - a high-reliability trial that randomly assigns participants to compare effects.

C Weak

Moderate

There is one reasonably well-designed trial. In a 12-month randomized double-blind study of 131 postmenopausal women with reduced bone density, 5 g/day of specific collagen peptides (SCP) significantly raised spine and femoral-neck bone density versus placeboAn inert dummy treatment used as the comparison baseline. (P=0.030 and P=0.003) and increased a bone-formation marker (P1NP). However, this is a single 12-month study of 131 people, and the authors include an affiliation with a collagen research institute (CRI GmbH), a conflict of interest to weigh. Independent replication and confirmation of real outcomes such as fractures remain to be done. PMID: 29337906

Evidence limits: reliance on industry funding and surrogate endpointAn intermediate measure (e.g., skin elasticity readings, bone density) used in place of a final outcome; it does not always track real clinical benefit.s (what the belief rests on)Evidence type: Expert review

D Insufficient

Minimal

Looking coolly at the collagen evidence, two things stand out. First, the positive results rest largely on surrogate endpointAn intermediate measure (e.g., skin elasticity readings, bone density) used in place of a final outcome; it does not always track real clinical benefit.s - instrument-read intermediates such as skin elasticity and hydration readings, bone density, and composite scores, rather than long-tracked real outcomes (how wrinkles affect life, fewer fractures). Second, many key trials are short (skin studies 8 weeks to 90 days), use a particular brand of collagen peptide, and some include authors affiliated with collagen manufacturing or research institutes. Even authors of one skin study noted that anti-aging claims are many while the research supporting them is limited. In short, rather than the simple expectation that eating it becomes skin and joint collagen, one should weigh the independence of the evidence and the nature of the measures. PMID: 23949208 · 29337906

Skin/joint benefit from eating collagen-rich foods (trotters, bone broth)Evidence type: Observational

D Insufficient

None

The belief that collagen from trotters or bone broth is good for skin has weak support. Two things must be separated. First, absorption: ingested collagen is mostly broken into amino acids, but some hydroxyproline (Hyp)-containing peptides (mainly Pro-Hyp) survive digestion and are actually detected in blood (plasma 20-60 nmol/mL at 1-2 h after ingesting 9.4-23 g of gelatin hydrolysate), so 'all broken down and useless' is an overstatement. Second, the source: the studied effects (on surrogate endpointAn intermediate measure (e.g., skin elasticity readings, bone density) used in place of a final outcome; it does not always track real clinical benefit.s) came from taking 2.5 to 10 g/day of hydrolyzed collagenCollagen broken into small fragments (collagen peptides), used in supplements to improve absorption. peptides at defined doses, not ordinary cooked foods. Bone broth, even made to a standardized recipe, provides significantly less of the key collagen amino acids than a reference research dose (a 20 g supplement) and varies widely by recipe, making it an unreliable source. There is also no evidence that absorbed amino acids go specifically to the skin, and trotters carry plenty of fat and sodium. PMID: 16076145 · 29893587

Evidence strength A Strong · B Moderate · C Weak · D Insufficient/refuted

Effect size Large → None

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Who benefits / who should be cautious

The statements in this section are translated directly from institutional sources (NIH-ODS, etc.), not our own interpretation. Consult a professional before use.

Caution

Anti-aging supplement claims are many, but the research supporting them is itself limited, as the authors of one skin study noted at the outset. It is better to check the amount and quality of the actual evidence than the advertising copy. source↗

Original text

Various dietary supplements are claimed to have cutaneous anti-aging properties; however, there are a limited number of research studies supporting these claims.
Caution

In the osteoarthritisThe most common degenerative joint disease, in which cartilage wears down causing pain and stiffness (OA). meta-analysisA statistical synthesis combining results of multiple studies into one conclusion. the composite scores fell, but the pain and functional-limitation subscores were not statistically significant. The evidence is not consistent enough to say it clearly works for joint pain. source↗

Original text

whereas the pain (WMD - 0.22; 95% CI - 1.58, 1.13; p = 0.75) and functional limitation (WMD - 0.62; 95% CI - 5.77, 4.52; p = 0.81) subscores did not have significant differences.
Benefit

On safety, a skin trial using 2.5 to 5 g a day reported no side effects throughout. As a kind of protein it is generally well tolerated. source↗

Original text

No side effects were noted throughout the study.
Caution

The expectation of 'topping up collagen with trotters or bone broth' has weak support. Even a standardized bone broth is significantly lower in the key collagen amino acids than a reference research dose and varies widely by recipe, so it cannot reliably deliver the defined doses shown to work in trials. If you expect an effect, it makes more sense to use the studied form (hydrolyzed collagenCollagen broken into small fragments (collagen peptides), used in supplements to improve absorption. peptides) at a sufficient dose. source↗

Original text

If the intake of collagen precursors is proven to support the synthesis of new collagen in vivo, it is unlikely that BB can provide a consistently reliable source of key amino acids.

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Form & dosage evidence

Trial doses by effect

Skin (trial dose): Collagen peptides 2.5-5 g/day, 8 weeks to 90 days [23949208]
Bone density (trial dose): Specific collagen peptides 5 g/day, 12 months [29337906]

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Balanced conclusion

Collagen sits between 'no evidence at all' and 'proven,' leaning positive but on weak reliability. For skin, a meta-analysisA statistical synthesis combining results of multiple studies into one conclusion. of 19 RCTRandomized controlled trial - a high-reliability trial that randomly assigns participants to compare effects.s showed improvements in elasticity, hydration, and wrinkles, and a trial raised bone density in postmenopausal women over 12 months, so it is hard to call it useless. But three things should be kept in mind. First, most of the gains are instrument-read surrogate endpointAn intermediate measure (e.g., skin elasticity readings, bone density) used in place of a final outcome; it does not always track real clinical benefit.s (elasticity and hydration readings, bone density) rather than long-tracked real outcomes. Second, in the osteoarthritisThe most common degenerative joint disease, in which cartilage wears down causing pain and stiffness (OA). meta-analysis the total scores fell but the pain and function subscores were not significant, so the joint effect is inconsistent. Third, key trials are short, use a particular brand of peptide, and some include authors affiliated with collagen manufacturing or research institutes, so independence needs checking. Safety is generally good, as befits a protein. In short, one might expect a modest benefit on specific measures such as skin elasticity, but it is far from the simple belief that eating it directly becomes skin and joint collagen, and when using it, it is sensible to weigh both the nature of the evidence and the overstatement in advertising.

Apply - Get it from food

Collagen is a protein in animal connective tissue such as skin, tendon, and bone, found in bone broth, trotters, chicken skin, and gelatin. However, trusted food-composition databases including USDA FoodData Central do not carry per-food collagen content as a standard nutrient value. Moreover, ingested collagen is mostly broken down into amino acids during digestion (though some peptides such as Pro-Hyp are absorbed). Above all, ordinary cooked foods such as bone broth and trotters vary widely by recipe and fall short of the defined doses shown to work in trials, making them an unreliable source (see the 'benefit from eating foods' row in the effect table). We therefore do not present a fill-from-food table.

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Sources

Each source shows its one-line summary and key summary up front. Expand the collapsed section to read the original abstract. Every citation is verified by re-resolving through the API.

PMID 33742704 Effects of hydrolyzed collagen supplementation on skin aging: a systematic review and meta-analysis Meta-analysis · Int J Dermatol, 2021 19 RCTRandomized controlled trial - a high-reliability trial that randomly assigns participants to compare effects.s, 1,125 people (95% women) - hydrolyzed collagenCollagen broken into small fragments (collagen peptides), used in supplements to improve absorption. improved skin hydration, elasticity, and wrinkles vs placeboAn inert dummy treatment used as the comparison baseline., with hydration and elasticity confirmed in subgroup analysis (about 90 days).

Key summary

A systematic review and meta-analysisA statistical synthesis combining results of multiple studies into one conclusion. of hydrolyzed collagenCollagen broken into small fragments (collagen peptides), used in supplements to improve absorption. for skin aging. Pooling 19 double-blind placeboAn inert dummy treatment used as the comparison baseline.-controlled RCTRandomized controlled trial - a high-reliability trial that randomly assigns participants to compare effects.s (1,125 people aged 20 to 70, 95% women), it found favorable results versus placebo for skin hydration, elasticity, and wrinkles, with hydration and elasticity confirmed in subgroup meta-analysis. The authors concluded that 90 days of intake is effective at reducing wrinkles and improving elasticity and hydration. However, participants were almost all women and the outcomes are surrogate measures (skin biophysical parameters), and the brands and funding backgrounds of the individual trials should be weighed.

Show original abstract

Skin aging has become a recurring concern even for younger people, mainly owing to increased life expectancy. In this context, the use of nutricosmetics as supplements has increased in recent years. The objective of this study was to summarize the evidence on the effects of hydrolyzed collagen supplementation on human skin through a systematic review followed by a meta-analysis of clinical trials focusing on the process of skin aging. Eligible studies were randomized, double-blind, and controlled trials that evaluated oral supplementation with hydrolyzed collagen as an intervention and reported at least one of the following outcomes: skin wrinkles, hydration, elasticity, and firmness. After retrieving articles from the databases, 19 studies were selected, with a total of 1,125 participants aged between 20 and 70 years (95% women). In the meta-analysis, a grouped analysis of studies showed favorable results of hydrolyzed collagen supplementation compared with placebo in terms of skin hydration, elasticity, and wrinkles. The findings of improved hydration and elasticity were also confirmed in the subgroup meta-analysis. Based on results, ingestion of hydrolyzed collagen for 90 days is effective in reducing skin aging, as it reduces wrinkles and improves skin elasticity and hydration. ※ The abstract text as collected and stored via the API by the pipeline. The key summary is written based solely on this text.

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PMID 30368550 Effect of collagen supplementation on osteoarthritis symptoms: a meta-analysis of randomized placebo-controlled trials Meta-analysis · Int Orthop, 2019 Meta of placeboAn inert dummy treatment used as the comparison baseline.-controlled RCTRandomized controlled trial - a high-reliability trial that randomly assigns participants to compare effects.s - total WOMACA standard index scoring pain, stiffness, and function in knee or hip osteoarthritis. (-8.00) and VAS (-16.57) fell, but the pain (P=0.75) and function (P=0.81) subscores were not significant (only stiffness fell).

Key summary

A meta-analysisA statistical synthesis combining results of multiple studies into one conclusion. of oral collagen for osteoarthritisThe most common degenerative joint disease, in which cartilage wears down causing pain and stiffness (OA). symptoms (placeboAn inert dummy treatment used as the comparison baseline.-controlled RCTRandomized controlled trial - a high-reliability trial that randomly assigns participants to compare effects.s). The total WOMACA standard index scoring pain, stiffness, and function in knee or hip osteoarthritis. index fell significantly (mean difference -8.00, P=0.002) and the pain visual scale (VAS) also fell (-16.57, P<0.001). But in the WOMAC subscore analysis only stiffness fell significantly (P=0.01), while pain (P=0.75) and functional limitation (P=0.81) were not significant. The authors concluded that collagen improves symptoms on the total-score basis, but the inconsistency in the core subscores (pain and function) calls for cautious interpretation.

Show original abstract

PURPOSE: Osteoarthritis (OA) is one of the most common causes of disability and a prevalent chronic disease. The use of collagen is growing due to the satisfactory results in the treatment of OA. However, the possible beneficial effects of collagen for the treatment of OA are currently controversial. The aim of the present meta-analysis was to evaluate the effect of collagen-based supplements on OA symptoms. METHODS: PubMed-Medline, Scopus, and Google Scholar databases were searched for randomized placebo-controlled trials evaluating the effect of orally administered collagen on OA symptoms using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scale and/or the Visual Analog Scale (VAS). RESULTS: Collagen treatment showed a significant reduction in the score of total WOMAC index (WMD - 8.00; 95% CI - 13.04, - 2.95; p = 0.002). After subgroup analysis of the WOMAC subscores, the collagen supplementation revealed a significant decrease in the stiffness subscore (WMD - 0.41; 95% CI - 0.74, - 0.08; p = 0.01), whereas the pain (WMD - 0.22; 95% CI - 1.58, 1.13; p = 0.75) and functional limitation (WMD - 0.62; 95% CI - 5.77, 4.52; p = 0.81) subscores did not have significant differences. Finally, a significant reduction was found in the VAS score after collagen administration (WMD - 16.57; 95% CI - 26.24, - 6.89; p < 0.001). CONCLUSION: The results of this meta-analysis showed that collagen is effective in improving OA symptoms by the decrease of both total WOMAC index and VAS score. ※ The abstract text as collected and stored via the API by the pipeline. The key summary is written based solely on this text.

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PMID 23949208 Oral supplementation of specific collagen peptides has beneficial effects on human skin physiology: a double-blind, placebo-controlled study Randomized controlled trial · Skin Pharmacol Physiol, 2014 (proprietary collagen peptide) 69 women, 8 weeks - 2.5-5 g/day collagen peptides significantly raised skin elasticity vs placeboAn inert dummy treatment used as the comparison baseline.; moisture/evaporation did not reach significance; no side effects.

Key summary

A double-blind placeboAn inert dummy treatment used as the comparison baseline.-controlled RCTRandomized controlled trial - a high-reliability trial that randomly assigns participants to compare effects. of a specific collagen peptide for skin. 69 women aged 35 to 55 were split into 2.5 g, 5.0 g, and placebo for 8 weeks, with skin elasticity, moisture, water loss, and roughness measured by instrument. Both doses significantly improved skin elasticity versus placebo, and elasticity remained higher in older women even 4 weeks after the last dose. Moisture and evaporation trended positive but did not reach statistical significance. There were no side effects. The authors' own opening note that anti-aging claims are many while supporting research is limited, and the use of a proprietary peptide, should be weighed.

Show original abstract

Various dietary supplements are claimed to have cutaneous anti-aging properties; however, there are a limited number of research studies supporting these claims. The objective of this research was to study the effectiveness of collagen hydrolysate (CH) composed of specific collagen peptides on skin biophysical parameters related to cutaneous aging. In this double-blind, placebo-controlled trial, 69 women aged 35-55 years were randomized to receive 2.5 g or 5.0 g of CH or placebo once daily for 8 weeks, with 23 subjects being allocated to each treatment group. Skin elasticity, skin moisture, transepidermal water loss and skin roughness were objectively measured before the first oral product application (t0) and after 4 (t1) and 8 weeks (t2) of regular intake. At the end of the study, skin elasticity in both CH dosage groups showed a statistically significant improvement in comparison to placebo. After 4 weeks of follow-up treatment, a statistically significantly higher skin elasticity level was determined in elderly women. With regard to skin moisture and skin evaporation, a positive influence of CH treatment could be observed in a subgroup analysis, but data failed to reach a level of statistical significance. No side effects were noted throughout the study. ※ The abstract text as collected and stored via the API by the pipeline. The key summary is written based solely on this text.

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PMID 29337906 Specific Collagen Peptides Improve Bone Mineral Density and Bone Markers in Postmenopausal Women - A Randomized Controlled Study Randomized controlled trial · Nutrients, 2018 (note: authors include an affiliation with Collagen Research Institute, CRI GmbH) 131 postmenopausal women, 12 months - 5 g/day collagen peptides significantly raised spine and femoral-neck bone density vs placeboAn inert dummy treatment used as the comparison baseline. and increased a bone-formation marker (P1NP).

Key summary

A 12-month randomized double-blind placeboAn inert dummy treatment used as the comparison baseline.-controlled trial of specific collagen peptides (SCP) in postmenopausal women with reduced bone density. 131 women were split into 5 g/day SCP and placebo, with the primary endpoint the change in spine and femoral-neck bone density. In the SCP group, spine and femoral-neck density rose significantly versus placebo (P=0.030 and P=0.003), the bone-formation marker P1NP increased (P=0.007), and the bone-resorption marker CTX rose in the placebo group - a favorable shift toward formation. However, this is a single 12-month study and the authors include an affiliation with a collagen research institute (CRI GmbH), a conflict of interest to weigh.

Show original abstract

Introduction: Investigations in rodents as well as in vitro experiments have suggested an anabolic influence of specific collagen peptides (SCP) on bone formation and bone mineral density (BMD). The goal of the study was to investigate the effect of 12-month daily oral administration of 5 g SCP vs. placebo (CG: control group) on BMD in postmenopausal women with primary, age-related reduction in BMD. Methods: 131 women were enrolled in this randomized, placebo-controlled double-blinded investigation. The primary endpoint was the change in BMD of the femoral neck and the spine after 12 months. In addition, plasma levels of bone markers-amino-terminal propeptide of type I collagen (P1NP) and C-telopeptide of type I collagen (CTX 1)-were analysed. Results: A total of 102 women completed the study, but all subjects were included in the intention-to-treat (ITT) analysis. In the SCP group (n = 66), BMD of the spine and of the femoral neck increased significantly compared to the control group (n = 65) (T-score spine: SCP +0.1 ± 0.26; CG -0.03 ± 0.18; ANCOVA p = 0.030; T-score femoral neck: SCP +0.09 ± 0.24; CG -0.01 ± 0.19; ANCOVA p = 0.003). P1NP increased significantly in the SCP group (p = 0.007), whereas CTX 1 increased significantly in the control group (p = 0.011). Conclusions: These data demonstrate that the intake of SCP increased BMD in postmenopausal women with primary, age-related reduction of BMD. ※ The abstract text as collected and stored via the API by the pipeline. The key summary is written based solely on this text.

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PMID 16076145 Identification of food-derived collagen peptides in human blood after oral ingestion of gelatin hydrolysates Human absorption study · J Agric Food Chem, 2005 (Kyoto Prefectural University, industry-independent) After ingesting 9.4-23 g of gelatin hydrolysate, collagen peptides (mainly Pro-Hyp) appeared in blood (20-60 nmol/mL at 1-2 h) - proving some are absorbed intact rather than fully broken down.

Key summary

A study confirming in humans whether ingested collagen is actually absorbed. After a 12-hour fast, healthy volunteers ingested gelatin hydrolysates (9.4-23 g) from porcine skin, chicken feet, and cartilage; hydroxyproline (Hyp) peptides, negligible before intake, rose significantly to a peak of 20-60 nmol/mL in plasma at 1-2 h and fell to half by 4 h. The main blood constituent was Pro-Hyp, with small amounts of others such as Ala-Hyp. So the claim that collagen is 'all broken down into amino acids' is inaccurate - some di/tri-peptides survive digestion and enter the blood. But this only establishes absorption; it does not prove a specific tissue (skin) effect or a benefit from eating whole foods such as trotters.

Show original abstract

In the present study, we identified several food-derived collagen peptides in human blood after oral ingestion of some gelatin hydrolysates. Healthy human volunteers ingested the gelatin hydrolysates (9.4-23 g) from porcine skin, chicken feet, and cartilage after 12 h of fasting. Negligible amounts of the peptide form of hydroxyproline (Hyp) were observed in human blood before the ingestion. After the oral ingestion, the peptide form of Hyp significantly increased and reached a maximum level (20-60 nmol/mL of plasma) after 1-2 h and then decreased to half of the maximum level at 4 h after the ingestion. Major constituents of food-derived collagen peptides in human serum and plasma were identified as Pro-Hyp. In addition, small but significant amounts of Ala-Hyp, Ala-Hyp-Gly, Pro-Hyp-Gly, Leu-Hyp, Ile-Hyp, and Phe-Hyp were contained. ※ The abstract text as collected and stored via the API by the pipeline. The key summary is written based solely on this text.

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PMID 29893587 Bone Broth Unlikely to Provide Reliable Concentrations of Collagen Precursors Compared With Supplemental Sources of Collagen Used in Collagen Research Food composition analysis · Int J Sport Nutr Exerc Metab, 2019 (Australian Institute of Sport) Analysis of bone broth - even a standardized recipe provided significantly less of the key collagen amino acids than a reference research dose (20 g supplement), with wide variability by recipe = not a reliable source.

Key summary

A composition-analysis study testing whether bone broth is a reliable food source of collagen. Commercial and self-prepared samples were made to standardized and nonstandardized recipes and analyzed for key collagen amino acids (glycine, proline, hydroxyproline, etc.). Key finding: even bone broth made to a standardized recipe was significantly lower in these amino acids than a potentially therapeutic research dose (a 20 g collagen supplement) (p=0.003-0.004). Nonstandardized recipes varied widely. The authors concluded that even if dietary collagen precursors are proven to support new collagen synthesis, bone broth is unlikely to be a consistently reliable source of the key amino acids. This supports that ordinary cooked foods such as trotters and bone broth do not reliably deliver the defined doses shown to work in trials.

Show original abstract

Intake of dietary sources of collagen may support the synthesis of collagen in varying tissues, with the availability of key amino acids being a likely contributor to its effectiveness. This study analyzed commonly consumed preparations of bone broth (BB) to assess the amount and consistency of its amino acid content. Commercial and laboratory-prepared samples, made with standardized and variable (nonstandardized) protocols, were analyzed for key amino acids (glycine, lysine, proline, leucine, hydroxyproline, and hydroxylysine). The main finding of this study was that amino acid concentrations in BB made to a standardized recipe were significantly lower for hydroxyproline, glycine, and proline (p = .003) and hydroxylysine, leucine, and lysine (p = .004) than those provided by a potentially therapeutic dose (20 g) of reference collagen supplements (p > .05). There was a large variability in the amino acid content of BB made to nonstandardized recipes, with the highest levels of all amino acids found within the café-prepared varieties. For standardized preparations, commercial BBs were lower in all amino acids than the self-prepared varieties. If the intake of collagen precursors is proven to support the synthesis of new collagen in vivo, it is unlikely that BB can provide a consistently reliable source of key amino acids. Research on the provision of key amino acids from dietary sources should continue to focus on the standard sources currently being researched. ※ The abstract text as collected and stored via the API by the pipeline. The key summary is written based solely on this text.

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Revision history

The full history of when and how this ingredient's evidence changed (git commits = proof of trust).

2026-07-13 First edition from real PubMed data - four collagen effect assessments (skin elasticity/hydration/wrinkles B/moderate, osteoarthritis symptoms C/minimal, postmenopausal bone density C/moderate, evidence limits D/minimal). The de Miranda skin meta-analysis (33742704, 19 RCTs), Garcia-Coronado OA meta-analysis (30368550, total scores down but pain/function subscores not significant), Proksch skin RCT (23949208), and Konig bone-density RCT (29337906, CRI Collagen Research Institute COI). Key points: leans positive but is skewed to surrogate endpoints, short duration, and industry funding, and the OA total scores fell while the pain and function subscores were not significant. As a protein its safety is good. With no authoritative openFDA label, guidance is grounded in the Proksch and Garcia meta verbatim (limited research behind anti-aging claims, non-significant OA subscores, no side effects). Diet is absent (collagen is not USDA-tracked; present in bone broth and skin but without content values, and digested to amino acids). New category `protein`. Glossary tooltips (hydrolyzed collagen, bone density, surrogate endpoint). Citation integrity, compliance, i18n, and the dash/table conventions verified.
2026-07-13 Dietary-collagen debate enrichment - settled the 'trotter collagen is good for skin' vs 'digested and useless' question with real sources and added a fifth effect, 'benefit from eating foods (trotters, bone broth)' D/none. Grounding: Iwai 2005 (16076145, Kyoto Prefectural University, industry-independent: collagen peptides such as Pro-Hyp are detected in blood after gelatin-hydrolysate intake, refuting 'fully broken down') and Alcock 2019 (29893587, Australian Institute of Sport: bone broth, even standardized, is significantly lower and more variable in amino acids than the 20 g research reference, so not a reliable source). Added an Alcock verbatim guidance item (bone broth unlikely a reliable source) and refined diet.unavailable to note that some peptides are absorbed but trotters/bone broth cannot deliver the defined doses. Conclusion: the answer is a form-and-dose issue - effects were seen with defined doses of hydrolyzed peptides, not whole foods.

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