Collagen type I is the main form of collagen found in skin, tendon, ligament, and bone. It plays a major role as a scaffold in normal wound healing and is found in the extracellular matrix of blood vessels, skin, and other organs. It is found in collagen supplements and has been evaluated in clinical research [1,2].

Collagen type II is the main form of collagen found in cartilage. It is also found in other types of connective tissue but is primarily localized to the cartilage. It is found in collagen supplements and has been evaluated in clinical research [1,3].

One of the reasons for the increasing prevalence of collagen peptide products is the fact that collagen peptides are up to 90% absorbed when taken by mouth. After absorption, they are distributed to target organs, including the dermis, muscle, bone, liver, kidney, and brain. It is thought that higher concentrations of these peptides at target locations will increase the production of collagen at those sites [1].

Be aware that some products may be marketed as "vegan collagen" or "plant-based collagen." These products do not contain collagen. Instead, they typically contain ingredients that are intended to boost the production of collagen in the body. Most of these products contain vitamin C, along with various other botanical ingredients. However, there is currently a lack of evidence supporting the use of these ingredients for the promotion of collagen production [1].

Collagen types I and II, as well as collagen peptides, have been evaluated for use in knee osteoarthritis, with studies suggesting the potential for modest benefit with certain formulations [2,3].

Collagen type II is the only form of collagen that has been evaluated for use in rheumatoid arthritis (RA). Although the available research is mixed, the highest quality evidence suggests a lack of benefit [2].

Clinical research in adults with RA, some of whom were taking disease-modifying antirheumatic drugs (DMARDs), shows that taking chicken collagen type II 0.1–2.5 mg daily, or bovine collagen type II 0.1–0.5 mg daily, for six months does not improve clinical response rates based on the American College of Rheumatology (ACR) criteria when compared with placebo. Also, one clinical study in patients stabilized on methotrexate shows that switching to chicken collagen type II 0.5 mg daily increases disease activity when compared to continued treatment with methotrexate [2].

Some small, low-quality studies have suggested possible benefit with the use of collagen type II, but these findings are limited by poor study methodology. Also, when response rates are evaluated by the ACR criteria, any identified benefits seem to disappear [2].

Research in otherwise healthy athletes with joint pain suggests that collagen peptides may provide modest relief. A study in student athletes with joint pain shows that taking a specific product (FORTIGEL) providing collagen peptides 10 grams daily for 24 weeks modestly improves pain during movement and at rest when compared with placebo [1].

Oral collagen peptides, when taken in doses of 4–10 grams daily for 4 to 12 weeks, have been shown to improve skin hydration and elasticity in older adults. However, not all studies have evaluated the visual appearance of wrinkles, and it remains unclear whether collagen peptides can improve the appearance of wrinkles to a cosmetically significant degree [1].

The studies that have evaluated this endpoint were all conducted in women older than 40 years of age and have yielded conflicting findings. One small clinical study shows that taking a low molecular weight collagen peptide product (Evercollagen) 1 gram daily for 12 weeks modestly improves visual appearance of wrinkles around the eyes when compared with placebo [1].

Another small study evaluating collagen peptides made from porcine collagen type I (VERISOL) shows that taking 2.5 grams daily for eight weeks reduces eye wrinkle volume by 20% when compared with placebo [1]. Additionally, a small study evaluating fish scale-derived collagen peptides (Wellnex) shows that taking 5 grams orally daily for eight weeks modestly improves wrinkle depth and roughness, but not wrinkle volume, when compared with placebo. Conversely, one small study shows that taking a fish-derived collagen peptide product (Vinh Wellness Collagen) 10 grams daily for 12 weeks does not improve patient-reported measures of wrinkles when compared with placebo [1].

Collagen, however, is not a complete protein. It lacks tryptophan, an essential amino acid that acts as a precursor to niacin (vitamin B3) in the body. Thus, collagen protein should not be relied upon as the primary source of protein in the diet. Mixed protein products, which contain protein from various sources, including collagen, can provide a healthy mix of essential and nonessential amino acids. Similarly, a diet that incorporates collagen protein powder as only one source of dietary protein can also provide a well-balanced array of amino acids [6,7,8].

As noted, all collagen products, whether provided intact or as peptides, are derived from animal sources. This may be a cause for concern for some patients who follow a vegetarian or vegan lifestyle, as well as those who observe certain religious or cultural practices [1,2,3].

Some manufacturers prepare collagen products in accordance with specific practices, such as Kosher or Halal, and will indicate this on the product label. Products containing solely chicken-derived collagen can be considered for patients who abstain from consuming red meat. Similarly, some products provide collagen obtained solely from marine sources; this may be an alternative for patients who do not have restrictions related to the consumption of fish. Marine collagen is obtained from the skin and scales of finned fish. It is unclear if people with an allergy to finned fish might be at risk for an allergic reaction to marine collagen; use with caution [1,2,3].