Collagen has become one of the most popular supplements in recent years, especially among those looking to support joint and skin health. In 2019, global spending on collagen supplements hit $1.8 billion (yes, billion), reflecting a strong desire to restore what has been lost. [1]
Collagen is undeniably important. It accounts for two-thirds of the dry weight of cartilage in joints such as the knee and plays a major structural role in tendons, ligaments, and skin. Because collagen production naturally declines with age, supplementation does have a certain intuitive appeal.
But biology doesn’t always follow intuition.
Protein from any source is broken down into smaller peptides and amino acids, which are then absorbed. The body uses these amino acids to make the proteins it needs, including collagen. In other words, your body doesn’t simply shuttle collagen from your plate to your knees.
Complicating matters further, cartilage has limited regenerative capacity. A paper published in Science described cartilage as “intrinsically unable to heal.” [2] The paper concluded that, unlike bone, cartilage regeneration remains elusive even with technologies much more sophisticated than taking collagen supplements. [3]
Against that backdrop, the notion that a scoop of collagen powder might meaningfully repair joint tissue warrants closer scrutiny.
What the Research Says
Some studies, however, suggest a potential benefit. One meta-analysis concluded that “collagen is effective in improving OA [osteoarthritis] symptoms.”[4]
But a closer look reveals some important caveats. The literature is marked by inconsistency and several recurring red flags:
- Conflicts of interest: A substantial proportion of studies are funded by companies, or the authors were paid by companies that produce or sell collagen. This doesn’t necessarily negate the findings, but it does call into question the neutrality of their published results.
- Publication bias: Studies showing no benefit are often shelved and not published.
- Inconsistency: Longer, higher-quality trials show little to no benefit, while shorter studies report more favorable outcomes. Trials in which patients took lower amounts (2-10 grams per day) reported larger effects than those in which patients took higher amounts (10-40 grams per day). [5]
- Sample size issues: Trials involving only a few subjects showed benefit, while those with many subjects showed none. [6]
- Placebo effect: A 2020 study found reductions in reported knee pain with collagen use, but the placebo group experienced identical improvements. Moreover, collagen supplementation had no impact on inflammatory, cartilage, and bone biomarkers. [7]
- Ingredient stacking: Many products contain additional compounds such as vitamin C, CoQ10, chondroitin sulfate, and glucosamine, making it difficult to attribute any benefit specific to collagen.
A Grain of Truth
That said, there may be a tiny kernel of truth underlying the collagen narrative.
Collagen is rich in glycine and proline, two non-essential amino acids that play important roles in collagen synthesis. [8] Increasing intake of these amino acids could raise plasma levels and, in theory, support collagen production.
In support of this, a 2022 randomized, double-blind, placebo-controlled study found that supplementation with 12 grams of six non-essential amino acids (including glycine and proline) over 12 weeks significantly alleviated joint pain and discomfort in individuals with joint issues. [9] Notably, there were no adverse effects (such as those often associated with collagen supplementation).
Where It Gets Interesting: The Plant-Based Connection
Here’s where the story takes an unexpected turn.
Multiple studies have found that those consuming a plant-exclusive diet have higher circulating glycine levels than omnivores. [10,11] A 2025 twin study reported that individuals assigned to a vegan diet had 30% higher glycine levels, despite lower dietary intake. [10]
The proposed explanation? Differences in the gut microbiome. Specifically, the vegans had 50% lower levels of Bilophila wadsworthia, a gut microbe that degrades glycine in the host, which may help preserve circulating glycine in those consuming plant-based diets. [10]
In other words, the body’s ability to maintain key building blocks for collagen may depend less on consuming collagen itself and more on overall dietary patterns and gut health.
The Downsides of Collagen Supplements
Beyond questions of effectiveness, several concerns are worth noting.
- Potential negative cognitive effects: Collagen lacks tryptophan—the amino acid precursor to serotonin. (Serotonin is essential for memory and other brain functions.) One study found collagen supplementation reduced tryptophan levels and impaired memory performance. [12] (Pro tip: Seeds are a superior source of tryptophan due to their high tryptophan-to-amino acid ratio.)
- Heavy metal contamination: Analyses have found that a significant proportion (over 70%) contain detectable levels of lead, arsenic, and cadmium that exceed safety standards. [13]
- The source matters: Collagen supplements are often derived from a disturbing mix of animal parts—including skin, tendons, cartilage, bones, tails, scales, and even brains. [13,14] If people saw how these products were made, they would think twice about taking them.
Bottom Line
Collagen supplements are built on an intuitively plausible idea, but plausibility is not proof of efficacy.
If your goal is to support the body’s natural collagen production, consider a vegan collagen booster rich in glycine, proline, and cofactors—without the contaminants or ethical concerns.
In our book Staying in the Game, we devote an entire chapter to joint health—including the roles of nutrition, supplementation, and lifestyle strategies for preserving function and performance over time. Because ultimately, health is not built on a single ingredient. It’s built on daily practices and patterns—and healthy practices outperform powders.
References
- Sumesh, K., & Rodriguez Barroso, L.G., Sanchez, M.L. Collagen Supplement Market by Source (Marine & Poultry, Porcine, and Bovine), Form (Pills & Gummies, Powder, and Liquid/Drinks), and Concentration (Pharmacy, Specialty Store, and Online Store): Global Opportunity Analysis and Industry Forecast, 2021-2027. in Latest Reports (Allied Market Research, 2021).
- Huey, D.J., Hu, J.C. & Athanasiou, K.A. Unlike bone, cartilage regeneration remains elusive. Science 338, 917-921 (2012).
- von Hippel, P.T. Researching collagen to help his achy knees, a statistician explores the painfully weak evidence. in First Opinion(STAT, 2022).
- García-Coronado, J.M., et al. Effect of collagen supplementation on osteoarthritis symptoms: a meta-analysis of randomized placebo-controlled trials. Int Orthop 43, 531-538 (2019).
- Jabbari, M., et al. Is collagen supplementation friend or foe in rheumatoid arthritis and osteoarthritis? A comprehensive systematic review. Int J Rheum Dis 25, 973-981 (2022).
- von Hippel, P.T. Do collagen supplements reduce symptoms of osteoarthritis? Meta-analytic results do not support strong conclusions. Int Orthop 45, 3283-3284 (2021).
- Bongers, C., et al. Effectiveness of collagen supplementation on pain scores in healthy individuals with self-reported knee pain: a randomized controlled trial. Appl Physiol Nutr Metab 45, 793-800 (2020).
- de Paz-Lugo, P., Lupiáñez, J.A. & Meléndez-Hevia, E. High glycine concentration increases collagen synthesis by articular chondrocytes in vitro: acute glycine deficiency could be an important cause of osteoarthritis. Amino Acids 50, 1357-1365 (2018).
- Takeuchi, F., Takada, M., Kobuna, Y., Uchida, H. & Adachi, Y. Effects of non-essential amino acids on knee joint conditions in adults: A randomized, double-blind, placebo-controlled trial. Nutrients 14, (2022).
- Carter, M.M., et al. A gut pathobiont regulates circulating glycine and host metabolism in a twin study comparing vegan and omnivorous diets. medRxiv (2025).
- Fackelmann, G., et al. Gut microbiome signatures of vegan, vegetarian, and omnivore diets and associated health outcomes across 21,561 individuals. Nat Microbiol 10, 41-52 (2025).
- Sambeth, A., et al. Memory impairments in humans after acute tryptophan depletion using a novel gelatin-based protein drink. J Psychopharmacol 23, 56-64 (2009).
- The true content and faces behind America’s best-selling collagen. Vol. 2025 (Clean Label Project).
- Avila Rodríguez, M.I., Rodríguez Barroso, L.G. & Sánchez, M.L. Collagen: A review on its sources and potential cosmetic applications. J Cosmet Dermatol 17, 20-26 (2018).