Collagen for Tendons and Connective Tissue: An Evidence-Based Read

Educational journalism, not medical advice. Every claim here is checked against its cited sources by editor Timothy Bunce — a health writer, not a physician. It isn’t specific to your situation: for health decisions, talk to your own clinician. How we work →

Some links in this article are affiliate links. If you buy through one, The Beachside Reader earns a commission at no extra cost to you. It never changes which products we pick, or what we say about them. Full affiliate disclosure →

What collagen actually is

Collagen is a family of fibrous structural proteins (28 distinct types in humans, with types I, II, and III being the most abundant). Collagen accounts for roughly 30% of total body protein and dominates the protein composition of tendons (~70–80% of dry weight), ligaments, skin, bone organic matrix, and articular cartilage.

The amino acid composition of collagen is unusual: it’s rich in glycine, proline, and hydroxyproline, with relatively little of the essential amino acids that drive muscle protein synthesis. This is why collagen scores poorly on traditional protein-quality measures (PDCAAS, DIAAS): it’s an incomplete protein for muscle-building purposes. The interesting question is whether the specific amino acid profile of collagen has functional relevance for connective-tissue synthesis specifically — and the recent evidence suggests it does.

Forms of collagen supplementation

The supplement aisle offers several collagen products with meaningful differences:

• Hydrolyzed collagen peptides: collagen broken into smaller peptides (typically 2–5 kDa) by enzymatic hydrolysis. The form used in most athletic-performance research. Dissolves easily, neutral taste, ~10–20 g typical serving.
• Gelatin: partially hydrolyzed collagen; gels in cool water, dissolves in hot. Functionally equivalent to hydrolyzed collagen for amino acid delivery; less convenient for daily use. Lis & Baar 2019 used gelatin in this collagen-synthesis biomarker study.
• Bone broth: variable collagen content depending on preparation; often inadequate dose unless consumed in large volumes. Pleasant culinary option but not a reliable supplement vehicle.
• Marine collagen: from fish skin; predominantly type I. Some users prefer this for sustainability or dietary reasons. Head-to-head comparisons with bovine collagen are limited.
• Type II collagen (UC-II): a different product entirely — small dose (40 mg) of undenatured collagen, marketed for joint health via a proposed immune-tolerance mechanism rather than amino acid delivery. Not the same as the hydrolyzed peptides discussed above.

For tendon and connective-tissue outcomes, hydrolyzed collagen peptides and gelatin, at the 10–20 g amounts used in the trials, are the most studied forms.

The Shaw and Baar studies: what shifted the conversation

Until ~2015, the dominant view was that oral collagen was simply incomplete protein with no special connective-tissue benefit. Two lines of work changed that:

Shaw et al. 2017: bioavailability and synthesis

Keith Baar’s lab at UC Davis, working with Greg Shaw, demonstrated that vitamin C-enriched gelatin (15 g gelatin + 50 mg vitamin C) consumed 30–60 minutes before exercise doubled collagen synthesis as measured by serum markers in a controlled trial Shaw et al. 2017. The mechanism: vitamin C is a required cofactor for prolyl hydroxylase, the enzyme that hydroxylates proline residues in pro-collagen (essential for triple-helix formation). The researchers timed the dose before exercise on the rationale that loading temporarily increases blood flow to connective tissue; that part of the rationale is plausible but less well established than vitamin C’s cofactor role.

Lis & Baar 2019: comparing collagen forms

The follow-up work compared vitamin C-enriched gelatin, hydrolyzed collagen, and a gummy formulation in 10 recreationally active, uninjured men who completed a single 6-minute jump-rope bout after supplementation. It measured a blood biomarker of collagen synthesis — not tendon symptoms or clinical outcomes — and individual variability was large enough that no treatment reached statistical significance over placebo Lis & Baar 2019. The clinical evidence that collagen improves tendinopathy symptoms comes from separate trials that paired supplementation with supervised loading programs (see Praet et al. 2019, below).

Praet et al. 2019: rehab outcomes

Independent work from a Dutch group examined collagen peptide supplementation alongside a calf-strengthening rehabilitation program in a small group of adults with chronic Achilles tendinopathy. Results showed significantly greater improvement in VISA-A symptom and function scores for the group that received collagen peptides first (+12.6 points vs. +5.3 for the placebo-first group at three months) Praet et al. 2019. More participants in the collagen-first arm had returned to running by follow-up, but the authors note the group sizes were too small for a valid statistical comparison of that outcome, and treatment-satisfaction ratings were similar between groups. Sample sizes are modest; the VISA-A effect direction is consistent.

Other tissues

Beyond tendon, the collagen literature includes Bello & Oesser 2006:

• Cartilage and joint pain: a 24-week trial in athletes with activity-related joint pain reported modest improvements in joint pain with collagen hydrolysate (10 g/day in the study) Clark et al. 2008. The effects are small, and persistent joint pain, including osteoarthritis, deserves a clinician’s assessment rather than self-treatment.
• Skin elasticity and hydration: multiple RCTs show improvements at 2.5–10 g/day for 4–12 weeks. Effects are statistically significant but modest in clinical magnitude Proksch et al. 2014.
• Bone density: limited but suggestive evidence in postmenopausal women; the effect is small and the evidence base is weaker than for skin or tendon.

Dose, timing, and the vitamin C requirement

Dose

Most tendon and connective-tissue trials have used 10–20 g of hydrolyzed collagen peptides or gelatin per dose. Higher daily amounts have not been well studied, and there’s no evidence that more is better. Whether collagen is worth trying, and how much, is a question your clinician, pharmacist or a registered dietitian can help with — particularly if you have kidney disease, have been told to limit protein, or take regular medications.

Timing

The 30–60 minute pre-exercise window comes from the Shaw 2017 protocol. The proposed rationale is that blood flow to connective tissue during loading delivers the elevated circulating amino acids to tendon and ligament; it is a plausible mechanism rather than an established one.

The trials don’t tell us how to adapt the protocol to different training schedules, so treat any marketed dosing schedule as extrapolation rather than evidence.

Vitamin C cofactor

Roughly 50 mg of vitamin C taken with the collagen was the protocol used in the foundational research. Most adults eating typical diets already get enough vitamin C from food, and whether adding more alongside collagen changes outcomes for them hasn’t been tested. For scale, a kiwi or a small glass of orange juice supplies roughly that amount.

Who benefits and who probably doesn’t

The collagen evidence base is most relevant for:

• Active adults with tendon symptoms (patellar, Achilles, lateral epicondyle): the population where rehab outcomes are documented — alongside a loading program, not instead of one.
• Returning to sport after tendon injury: any supplement is best discussed with the physiotherapist or physician guiding your rehab.
• Sustained heavy training in tendon-stressing sports: jumpers, throwers, tennis players, marathoners.
• Postmenopausal women: some early research has looked at joint and bone outcomes in this group, but the evidence is limited; bone health and osteoporosis risk are best assessed with a clinician.
• Active adults with activity-related knee discomfort: a trial in young athletes reported less knee discomfort during activity with collagen peptides Zdzieblik et al. 2017. People with osteoarthritis should discuss treatment options with their clinician.

The collagen evidence is less compelling for:

• Pure muscle-building goals: collagen is an incomplete protein and inferior to whey or other higher-quality proteins for muscle protein synthesis. Not a replacement for protein in a hypertrophy program.
• General health in the absence of training: the evidence is built on training + collagen, not on collagen alone.
• Skin and beauty claims at low doses: real benefits exist but they’re modest; the marketing often overstates the magnitude.

Why loading matters more than the supplement

This is the part most marketing skips: the collagen evidence comes from people doing progressive tendon loading. The clinical evidence for the combination comes from a trial that layered collagen peptide supplementation on top of a calf-strengthening rehabilitation program for Achilles tendinopathy (Praet et al. 2019). The heavy-slow resistance approach described below is borrowed from a separate, collagen-free exercise trial in Achilles tendinopathy (Beyer et al. 2015) — it has not itself been tested in combination with collagen supplementation, and it did not include a patellar tendinopathy cohort Beyer et al. 2015. Without the loading, the collagen alone is unlikely to produce meaningful tendon improvement.

What tendon rehabilitation in that research looked like, in outline — a description of the studies, not a program to self-prescribe. Persistent or worsening tendon pain should be assessed by a physiotherapist or physician, who can tailor loading to you:

1. Identify the tendon: patellar (anterior knee at insertion), Achilles (posterior heel), proximal hamstring (sit-bone), tennis elbow (lateral epicondyle), golfer’s elbow (medial epicondyle), gluteal tendon (lateral hip).
2. Heavy-slow resistance: heavy loads in roughly the 6–12 RM range at a slow tempo (about 3 seconds lowering, 3 seconds lifting), about three sessions per week, progressed over time. Weighted heel raises are the classic Achilles example.
3. Progress over weeks: tendon adaptations are slow (8–12 weeks minimum); don’t expect rapid improvement.
4. Collagen as an add-on: in Praet et al. 2019 the collagen was added on top of the rehab program, not used in place of it; if you’re considering it, ask your clinician or pharmacist whether it suits you.
5. Monitor pain: rehab programs typically allow some discomfort during loading, within limits your clinician sets; pain that worsens through the next day, swelling, or pain at rest are reasons to back off and get reassessed.

The bigger framework: collagen is a small adjunct to a large mechanical and timeline-based intervention. Don’t skip the loading; don’t expect collagen alone to fix a tendon problem.

Product quality and how to choose

Collagen peptides are not a regulated supplement category in the way pharmaceuticals are, but the quality bar is generally adequate from reputable manufacturers. Considerations:

• Source: bovine (cow), porcine (pig), marine (fish). Head-to-head comparisons are limited; choose based on dietary preferences.
• Hydrolysis: most products are hydrolyzed; check that the molecular weight is in the 2–5 kDa range for absorption.
• Third-party testing: NSF Certified, Informed Sport, or similar testing protects against heavy metals and contaminants. Useful for athletes subject to anti-doping regulations.
• Flavoring: unflavored is typical; some products are flavored for ease. The unflavored versions mix well into coffee, oatmeal, or smoothies without altering taste meaningfully.
• Cost per gram of collagen: this is the practical comparison. Calculate cost per 20 g serving for honest comparison across products.

What the research protocol looks like in a training week

Pulled together, this is how the research protocols map onto a training week. It’s a framework to discuss with a physiotherapist or sports-medicine clinician, not a treatment plan:

• Before loading sessions: the trials used 15–20 g of hydrolyzed collagen or gelatin with about 50 mg of vitamin C, 30–60 minutes beforehand. Whether and how much you take is a decision for you and your clinician or pharmacist.
• During session: the loading work your physiotherapist or clinician has set for the affected tendon.
• Post-session: standard recovery (protein, carbohydrate, hydration). Collagen is not the post-workout protein source.
• Sleep: tendon recovery depends on sleep; the standard 7–9 hours applies.
• Review progress with your clinician: tendon adaptations are slow, so changes are usually judged over 8 weeks or more; get reassessed sooner if pain is worsening.

At most, collagen is a modest addition to a properly planned rehab or training program. The size of effect is real but moderate; expectation calibration matters.

Practical logistics and edge cases

Beyond the core protocol, several considerations come up for adults adding collagen.

Collagen and total protein intake. Don’t count collagen toward your daily protein target for muscle-building purposes; it’s an incomplete protein. If you’re already meeting your total protein needs, collagen is a small addition without displacing higher-quality sources.

Vegetarian and vegan options. True collagen is animal-source. Plant “collagen boosters” (vitamin C, silica, amino acids) are marketed as supporting the body’s own collagen synthesis, but they don’t replace direct collagen peptides. Marine algae and some fungal sources are being studied; the evidence base is limited.

Side effects. Collagen is generally well-tolerated. Mild GI upset (bloating, fullness) is the most common side effect; usually resolves with smaller divided doses or different brand. Allergic reactions are rare but possible (more common with marine collagen for fish-allergic individuals).

Pregnancy and breastfeeding. Collagen supplements have not been well studied in pregnancy or breastfeeding, so their safety at supplement doses isn’t established. Talk to your physician, midwife or pharmacist before using one.

Coffee compatibility. Hydrolyzed collagen mixes well into hot coffee without curdling. The vitamin C cofactor is heat-sensitive though — if you’re using vitamin C powder, add it to a slightly cooled coffee or take separately.

Long-term safety. Collagen and gelatin have long been part of the food supply, and the supplement trials have reported few side effects over their durations of weeks to months. Longer-term data on regular high-dose supplement use are limited. If you have kidney or liver disease, have been told to limit protein, or take regular medications, check with your clinician or pharmacist first.

Combining with creatine and protein. Collagen, standard protein, creatine and carbohydrate address different things, and there’s no known reason they would interfere with one another, but the combinations haven’t been studied much. If you take several supplements or any medications, a pharmacist can check them for you.

Practical takeaways

• The studied protocol: 15–20 g of hydrolyzed collagen or gelatin with about 50 mg of vitamin C, 30–60 minutes before loading, is what the tendon and connective-tissue trials used; the benefits seen were modest and the trials small.
• Loading comes first: tendon problems are managed with progressive loading, ideally planned by a physiotherapist or physician; collagen alone is unlikely to fix tendon symptoms.
• Most benefit: athletes with tendon symptoms, post-injury rehab, sustained heavy training in tendon-stressing sports.
• Less benefit: pure muscle-building goals (collagen is incomplete protein), general health in untrained adults.
• Vitamin C cofactor matters: prolyl hydroxylase requires vitamin C; the foundational studies paired collagen with about 50 mg, and most adults already get at least that much from food.
• Tendon adaptations are slow: 8–12 weeks minimum; expect compounding rather than immediate effects.
• Quality bar: third-party tested products from reputable brands; choose bovine, porcine or marine by dietary preference, as head-to-head comparisons are limited.

A closing note on revisiting this article

The collagen literature has shifted meaningfully in the last decade and continues to evolve. The Shaw and Baar work (2017–2019) brought mechanistic and outcome evidence into a space dominated by marketing claims; subsequent research has refined the protocol and clarified the populations most likely to benefit. We will revise this article as additional RCTs accumulate, particularly in populations beyond tendinopathy (cartilage, bone, post-surgical recovery). The current best read is captured above; the broad direction (collagen + vitamin C + loading produces modest connective-tissue benefits) is unlikely to reverse, though magnitudes may refine as evidence grows.

References