The 9 Best Collagen Powders of 2023

Vital Protein Collagen Peptides is high in protein and NSF certified for sport

We independently research, test, review, and recommend the best products. Healthcare professionals review articles for medical accuracy. Learn more about our process. If you buy something through our links, we may earn a commission.

Vital Proteins Collagen Peptides Powder Supplement

Verywell Health / Peter Ardito

Collagen is the most abundant protein in our bodies—it gives structure to our connective tissue, bones, skin, hair, and nails. Collagen supplements can support collagen production and may reduce wrinkles and joint pain and improve nail strength and bone density. Collagen production also naturally declines as we age, so some people turn to collagen powders to boost production.

While collagen powders may be beneficial, they are made from animal tissue, so they're not appropriate for those following strict vegan or vegetarian diets. They can also be expensive. So it may be comforting to know that consuming collagen powders is not necessary. “Our bodies make collagen using the building blocks zinc, vitamin C, copper, and amino acids. Eating a well-balanced diet rich in fruits, vegetables, and a variety of protein sources can supply your body with the building blocks to support collagen formation,” says Jamie Adams, MS, RDN, LDN.

To compile a list of the best collagen powders, our research-savvy dietitian combed through dozens of products and clinical studies and interviewed experts in the field. When choosing a collagen powder, consider type (different types offer different possible benefits), source (bovine, eggshell, fish, chicken), and other ingredients in the powder.

Always speak with a healthcare professional before adding a supplement to your routine to ensure that the supplement is appropriate for your individual needs, and to find out what dosage to take.

Best Overall

Vital Proteins Original Collagen Peptides

Vital Proteins Collagen Peptides


  • NSF Certified for sport

  • Grass-fed and pasture-raised bovine peptides

  • Good source of protein

  • Not a good source of type II collagen for joint health

Vital Proteins Collagen Peptides is our top choice because it is NSF certified for sport and gives you 18 g of protein with no added sugar or artificial sweeteners. It’s not only a great option for adding collagen but also gives you a good dose of protein if you’re looking to up your intake. Importantly, it’s third-party tested and NSF Certified for Sport, so you can trust that it contains what the label says and has no other harmful ingredients or contaminants.

Vital Proteins Collagen Peptides contain types I and III collagen made from bovine hide, which is said to support skin, nail, and hair health. It contains 100% of your daily vitamin C needs, which can support collagen production, as well as hyaluronic acid, which may reduce wrinkles.

This product is also gluten-free, dairy-free, and certified kosher.

Price at time of publication: $50 ($1.79 per serving)

Dose: 2 scoops 20 g | Servings Per Container: 28 | Active Ingredients: Hydrolyzed collagen, hyaluronic acid, vitamin C, sodium | Gluten-free: Yes | Other Ingredients: None

Best for Athletes

Momentous Collagen Peptides

Momentous Collagen Peptides


  • NSF Certified for sport

  • Collagen from grass-fed bovine

  • Good source of protein and vitamin C

  • Suggested to take one hour before exercise

Momentous Collagen Peptides is a good choice for both active people and competitive athletes. It’s NSF Certified for Sport, a rigorous third-party certification that ensures the supplement contains what the label says (with no hidden extras) and doesn’t contain any substances that are banned by sport. It’s also certified by Informed Sport, another third-party testing company that tests for over 250 substances banned by sport. 

It contains 15 grams of protein from a mix of collagen peptides from grass-fed bovine and FORTIGEL collagen hydrolysate. FORTIGEL, a specific type of collagen peptide, has been shown to stimulate collagen production in tendons and reduce knee and joint pain in healthy athletes. 

It has no added sugar, is gluten-free, and contains 50% of your daily vitamin C needs to support collagen production. It does contain a small amount of sodium, which may be helpful to replace some of the sodium lost in sweat. Since this collagen powder is designed for athletes, the recommended serving suggestion is specific to take one hour before exercise for best results.

Price at time of publication: $52 ($1.73 per serving)

Dose: 1 scoop 16.9 g | Servings Per Container: 30 | Active Ingredients: Collagen peptides, FORTIGEL, vitamin C, sodium | Gluten-free: Yes | Other Ingredients: None

Best Single Ingredient

Besha Natural Collagen Peptides

Besha Natural Collagen Peptides


  • Third-party tested

  • Collagen is the only ingredient

  • Not a good source of protein

For a simple collagen powder that doesn’t contain any extras, we recommend Besha Collagen Peptides. It’s a third-party tested for purity and potency and made from a specific collagen peptide known as Verisol, which may help reduce wrinkles. One small study among middle-aged women showed that daily consumption of 2.5 g of Verisol reduced eye wrinkles and increased elastin production.

However, with only 2.6 g of protein per serving, Besha is not a good source of protein for those that rely on collagen powders to help them meet their daily protein needs.

Price at time of publication: $24 ($0.71 per serving)

Dose: 2.9 g | Servings Per Container: 34 | Active Ingredients: Verisol collagen peptides | Gluten-free: Yes | Other Ingredients: None

Best Flavored

Klean Athlete Collagen + C

Klean Athlete Collagen + C


  • NSF Certified for sport

  • Good source of protein

  • Contains 56% of daily vitamin C needs

  • Expensive

If you prefer a flavored powder, Klean Athlete Collagen + C is a good choice. It contains 15 g of hydrolyzed collagen and 56% of your daily vitamin C needs. The berry flavor comes from pomegranate juice, blackberry juice, beet powder, and other natural flavors. It is sweetened with monk fruit extract, which is generally recognized as safe (GRAS) by the FDA, though some people don’t love the flavor of this alternative sweetener.

Klean Athlete Collagen + C can be added to water or smoothies for both a flavor and protein boost, with 14 grams of protein per serving. It’s also gluten-free, non-GMO, and contains less than 1 gram of added sugar.

Price at time of publication: $39 ($1.95 per serving)

Dose: 1 scoop 17 g | Servings Per Container: 20 | Active Ingredients: Hydrolyzed collagen | Gluten-free: Yes | Other Ingredients: Natural flavors, organic pomegranate juice, organic blackberry powder, beet juice powder, citric acid, monk fruit extract

Best Multi-Source

CB Supplements Multi Collagen Protein

CB Supplements Multi Collagen Protein


  • NSF Certified for sport

  • Contains five types of collagen

  • Collagen from grass-fed, wild-caught, cage-free animals

  • Not suitable for someone with a fish or egg allergy

  • Expensive for higher dosage

CB Multi Collagen Protein contains collagen peptides from four different sources: bovine (cow), fish, eggshell, and chicken, which provides collagen types I, II, III, V, and X. With 7 g of protein per scoop, it’s a reasonably good source of protein and may offer a wider range of benefits than some other collagen powders with only one or two types of collagen.

It’s NSF Certified for Sport, non-GMO, and gluten-free but does contain fish and egg allergens. The recommended dose is one scoop per 50 pounds of body weight (up to four scoops per day), which can get expensive and is a lot to consume if you’re aiming for three or four scoops per day.

Price at time of publication: $60 ($1.03 per serving)

Dose: 2-4 scoops 15.6-31.2 g | Servings Per Container: 14-29 | Active Ingredients: Multi Collagen Complex | Gluten-free: Yes | Other Ingredients: None

Best Complete Protein

Shaklee Collagen-9

Shaklee Collagen-9


  • Contains all nine essential amino acids

  • Biotin may support nail and hair

  • No artificial flavors, sweeteners, colors, or preservatives

  • Not third-party verified

“Most collagen powders are incomplete proteins—meaning they do not contain all nine essential amino acids that our bodies are unable to produce on their own,” says Amy Gorin, MS, RDN, an inclusive plant-based dietitian and owner of Master the Media. Shaklee Collagen-9 contains both hydrolyzed collagen and pea protein, providing all nine essential amino acids and a complete source of protein. It also contains biotin, which may support hair and nail growth.

Shaklee Collagen is not third-party verified by USP, NSF, or, but they do their own quality testing, including tests for harmful contaminants. Shaklee is a carbon-neutral company and is invested in the health of both people and the planet.

Price at time of publication: $35 ($1.75 per serving)

Dose: 2 scoops 11.6 g | Servings Per Container: 20 | Active Ingredients: Hydrolyzed collagen, biotin, vitamin C | Gluten-free: Not certified | Other Ingredients: Pea protein

Best Marine

Procaps Marine Collagen Peptides

Procaps Marine Collagen Peptides


  • Third-party tested

  • Suitable for pescatarians

  • Collagen peptides is only ingredient

  • Budget friendly

  • Not suitable for someone with a fish allergy

If you’re pescatarian or prefer to avoid products made from cow, pig, or chicken, Procaps Marine Collagen Peptides may be a good choice for you. Its simple ingredient list (just collagen peptides) is a bonus. It has a neutral taste, so don’t worry—it won’t impart a fish flavor on your morning coffee or smoothie.

Marine Collagen Peptides are third-party tested for purity and potency, non-GMO, and contain 5 g of collagen peptides to support collagen production.

Price at time of publication: $55 ($0.92 per serving)

Dose: 1 scoop 5 g | Servings Per Container: 60 | Active Ingredients: Marine collagen peptides | Gluten-free: Not specified | Other Ingredients: None

Best for Travel

Gnarly Collagen Pro

Gnarly Collagen Pro


  • NSF Certified for sport

  • Mixes into cold or hot beverages

  • Individual packets make it portable

  • Not a good source of type II collagen for joint health

  • Expensive

Gnarly Collagen Pro travel packs are easy to take with you whether you’re traveling, on a long hike, or just regularly on the go. One packet contains 15 g of hydrolyzed collagen (14 g of protein) along with vitamin C, zinc, and copper to support collagen production. It’s unflavored, so it can be mixed into coffee, smoothies, sports drinks, or any other liquid of choice.

Gnarly Collagen Pro is NSF Certified for Sport and NSF Contents Certified, meaning it’s been tested for harmful contaminants, microbes, and pesticides, as well as any ingredients banned by sport.

Price at time of publication: $48 ($1.60 per serving)

Dose: 1 packet 15g | Servings Per Container: 1 | Active Ingredients: Hydrolyzed collagen, zinc, vitamin C, sodium, copper | Gluten-free: Not specified | Other Ingredients: None

Best Sustainable

Nordic Naturals Marine Collagen Powder

Nordic Naturals Marine Collagen Powder


  • Third-party tested

  • Contains vitamin C

  • Collagen from sustainable, wild-caught Arctic cod

  • Not suitable for someone with a fish allergy

If you are looking for a sustainable source of collagen, we recommend Nordic Naturals Marine Collagen Powder, as the company is committed to reducing their environmental impact. All sourced fish are from certified sustainable fisheries and are wild-caught, non-endangered species. Their manufacturing facilities use biofuel for energy and their headquarters are Gold certified through the U.S. Green Building Council’s LEED (Leadership in Energy and Environmental Design) Rating System. Nordic Naturals farther minimizes their carbon footprint by packaging all products in recyclable containers and even supporting other organizations prioritizing environmentally friendly practices.

This collagen powder specifically provides 4,200 mg of hydrolyzed collagen peptides with no artificial ingredients and a mild strawberry flavor. It also contains 45 mg of Vitamin C to aid in absorption, which is 50% of your daily needs.

You can visit the Nordic Naturals website to view certificates of analysis for any of their third-party tested products.

Price at time of publication: $33 ($1.10 per serving)

Dose: 2 teaspoons (5 g) | Servings Per Container: 30 | Active Ingredients: Hydrolyzed collagen, vitamin C | Gluten-free: Not certified | Other Ingredients: Natural flavor, stevia glycosides, beetroot extract

Are Collagen Powders Beneficial?

The research on collagen supplements is still evolving, though some studies have shown promise. It’s helpful to understand that “our bodies do not directly absorb collagen in powder form to be used immediately by our skin, bones, and joints. Rather, our bodies break collagen in powder form down into amino acids (the building blocks of collagen). These are then used by the body, along with zinc, vitamin C, and copper, to re-synthesize collagen, which can then be used by the body,” says Adams.

Therefore, prioritize consuming enough protein and other nutrients that support collagen production. Collagen powders are often a good source of protein and provide the amino acids our bodies need to create collagen.

In general, human studies looking at the health and appearance benefits of collagen are small, short, and conducted in very specific groups of people (often older women). Larger and longer studies are needed to support recommending collagen powders for these benefits. It’s also important to note that there haven’t been any studies to support the use of collagen supplements for improving gut health.

There are 28 types of collagen, but the most common types are types I through IV, with type I making up almost 90% of the collagen found in our bodies.

Collagen supplements may benefit:

Skin appearance. Because of its role in skin elasticity, collagen has long been used in skincare products for wrinkle prevention. Some studies have shown that oral collagen—types I and III—improve skin appearance and elasticity. The benefits seem to be more pronounced in older women (usually post-menopausal) whose skin has sun damage. Other studies have shown that various forms—bovine (cow), porcine (pig), and marine (fish)—may improve elasticity and reduce wrinkles.

Hair and nail strength. Results from small studies show that collagen supplements may improve brittle nails or increase nail growth. But other studies have shown no benefit. Since our hair is primarily made of keratin, and many of the amino acids found in keratin are also found in collagen, it’s plausible that consuming collagen could support hair growth. A small study supports this theory, where those who supplemented with oral collagen for 12 weeks had hair that appeared thicker and had less breakage. 

Bone density in post-menopausal women. Most research on the benefits of collagen on bone density has been in animals, but one small study among post-menopausal women with decreased bone density did see a benefit to taking 5 g of collagen peptides per day.

Those with joint pain. Collagen may reduce symptoms of osteoarthritis. It’s also been shown to reduce activity-related joint pain and improve joint movement.

Pregnant and breastfeeding people. “Currently, there is limited research on the safety of taking collagen powders during pregnancy or while breastfeeding. However, at the moment there are no known side effects of using collagen powder during pregnancy or while breastfeeding,” says Adams.

Protein needs are higher in the later stages of pregnancy and while breastfeeding, and new research suggests that breastfeeding people may need up to 1.7 g of protein per kilogram of body weight, which is similar to the needs of serious athletes. Collagen powders may be a helpful way for some people to meet those higher needs.

If you are pregnant or breastfeeding, always consult with a healthcare provider before adding a supplement, and be sure to choose one that is third-party verified by a reputable source, so you know it doesn’t contain any potentially harmful ingredients.

Who May Not Benefit from Collagen Powders

Collagen powders are generally safe for most people and are well tolerated without side effects. However, there are certain people who may want to avoid collagen powders. 

Vegans or vegetarians. Currently, the collagen powders on the market are made from animal or marine sources, so they are not appropriate for someone who avoids those foods. 

People with certain food allergies. Many collagen powders contain either egg or fish, which would not be safe for someone with an allergy to either of those foods. In addition, not all are gluten-free or free from other ingredients like dairy and soy, so always read labels to verify a product is safe for you.

How We Select Supplements

Our team works hard to be transparent about why we recommend certain supplements; you can read more about our dietary supplement methodology here

We support supplements that are evidence-based and rooted in science. We value certain product attributes that we find to be associated with the highest quality products.

It's important to note that the FDA does not review dietary supplements for safety and effectiveness before they go to market. Our team of experts has created a detailed, science-backed methodology to choose the supplements we recommend.

What to Look for in Collagen Powders

Third-Party Testing

Supplements that are third-party tested are sent to a lab where they are tested to ensure they contain what they say they contain and are not contaminated with specific high-risk, common contaminants. However, it’s important to note:

  • Third-party testing does not test to see if a product is effective or safe for everyone, and it does not ensure the supplement will not interact with other supplements or medications.
  • Not all third-party testing is created equal. It is not uncommon for supplement companies to pay labs for certificates after conducting minimal to no testing. 
  • The third-party certifications we can trust are:, NSF, and USP. However, these certifications are difficult to obtain and/or expensive for manufacturers, so many companies choose not to get their products tested by one of these three organizations. 
  • Sometimes products tested by these three companies are more expensive to try to offset the cost they pay for certification.
  • Just because a supplement is not tested by one of these three companies does not mean it’s a bad product. We recommend doing some research on the reputability of the manufacturer and calling up the manufacturer and their testing lab to determine their protocols and decide if you feel comfortable consuming the supplement.


Collagen powders are typically derived from bovine (cow), porcine (pig), eggshell, and marine (fish) sources and usually provide types I, II, and III collagen. Types I and III are used to support skin, hair, and nail health, whereas type II is used for joint health and bone density.  Some powders also contain type V and X collagen, though those are less common. 

There are three types of collagen that might be used in collagen supplements: collagen peptides, gelatin, and raw or undenatured collagen. However, all powder supplements we came across contain collagen peptides, also known as hydrolyzed collagen. This is collagen that is broken down into smaller units (peptides) and is said to be more absorbable than raw collagen, though research to support this is limited.

Ingredients and Potential Interactions

It is essential to carefully read the ingredient list and nutrition facts panel of a supplement to know which ingredients and how much of each ingredient is included relative to the recommended daily value of that ingredient. Please bring the supplement label to a healthcare provider to review the different ingredients contained in the supplement and any potential interactions between these ingredients and other supplements and medications you are taking.

  • Vitamin C. Many collagen supplements contain vitamin C to enhance absorption. Vitamin C is a water-soluble vitamin and is generally safe for most people. However, too much vitamin C in supplement form can lead to nausea, vomiting, and diarrhea, so be mindful about using collagen powders along with other vitamin C supplements.
  • Zinc. Some collagen supplements also contain zinc. Too much zinc (more than 40 mg) in supplement form can lead to nausea, vomiting, and diarrhea, so pay attention to how much you’re taking from supplements.
  • Digestive enzymes. Some collagen powders also contain digestive enzymes. In general, digestive enzymes provide no benefit to healthy people, and only specific enzymes help people with specific conditions when eating specific foods. While they are generally seen as safe, some people do experience unwanted digestive side effects, so it’s something to be aware of and possibly avoid.

Other ingredients that you may want to be aware of include added sugar and alternative sweeteners. While they are generally safe, some people prefer to avoid them, so it’s important to read ingredient labels. 

Collagen Powder Dose

Since collagen does not need to be consumed orally, there is no established dose. The amount of collagen powder that is recommended varies by type and use. Most studies use between 5 to 15 g of collagen peptides or hydrolyzed collagen. However, lower doses (2.5 g) of specific collagen peptides Verisol has been shown to potentially offer some skin benefits.

How Much Is Too Much?

Collagen powders are generally well tolerated by most people, and there is no specific upper limit defined since protein needs vary by person. It can contribute a good source of protein to your diet for people that otherwise don’t get enough. However, it shouldn’t be the only source of protein since it’s not a complete protein, and it’s best to get your protein from a variety of food sources. Research has shown that up to 36% of your protein intake can come from collagen peptides without sacrificing overall diet needs for a mix of amino acids, so it’s best not to exceed that amount.

Frequently Asked Questions

  • Can you take collagen and protein powder together?

    It is safe to mix collagen and other protein powders together. “It may even be beneficial as you are providing your body with a more diverse range of amino acids. However, you want to be mindful about the total protein load,” says Adams. It’s best to get protein from a variety of food sources and use powders as a way to supplement your diet to meet your total needs.

  • Can collagen powder cause constipation?

    There are currently no studies to suggest that collagen powder causes constipation. “Collagen powders contain ample protein. If you’re increasing your protein intake but not choosing to do so in a way that also increases your fiber intake, then this could indirectly cause constipation as you need fiber to help move food through your body,” says Gorin.

  • What can you put collagen powder in?

    Collagen powders made from collagen peptides can be mixed into hot or cold beverages. Unflavored powders are best mixed into something that adds flavor, such as a smoothie, oatmeal, or yogurt. Some people like to mix collagen into their coffee for a protein boost in the morning. Flavored options can be mixed with water or any other liquid of choice. Partially hydrolyzed collagen doesn’t dissolve well in cold liquids, so they are best mixed into warm beverages or foods like tea, coffee, or broth.

  • How can I mix collagen powder without clumping?

    For warm beverages, collagen can easily be stirred in with a spoon. Cold beverages may blend better in a blender, with a protein powder shaker, or with a whisk.

  • How much does collagen protein powder cost?

    The cost of collagen protein powder depends on the size of the container, recommended serving size, and the type of ingredients used. In general, a serving of collagen protein powder can range from under a dollar per serving to $2 per serving. Our best overall pick, Vital Proteins collagen peptide, is on the higher end around $1.77 per 20 gram serving. However, the collagen source is grass fed cows, and this product is third party tested. The Besha collagen peptides cost is on the lower end of cost, about $0.76 per serving, but the serving size is only about 3 grams.

Why Trust Verywell Health

Sarah Anzlovar, MS, RDN, LDN, is a registered dietitian with her master's degree in nutrition communication from the Tufts Friedman School of Nutrition Science and Policy. She owns a private practice in the suburbs of Boston, where she helps her clients ditch diets and learn to eat foods that help them feel their best and achieve optimal health. Sarah is also a freelance writer, where she lends her expertise in translating the research on a wide variety of nutrition topics into relatable and approachable recommendations for consumers.

26 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. García-Coronado, J.M., Martínez-Olvera, L., Elizondo-Omaña, R.E. et al. Effect of collagen supplementation on osteoarthritis symptoms: a meta-analysis of randomized placebo-controlled trials. International Orthopaedics (SICOT) 43, 531–538 (2019). doi:10.1007/s00264-018-4211-5

  2. König, D., Oesser, S., Scharla, S., Zdzieblik, D., & Gollhofer, A. Specific collagen peptides improve bone mineral density and bone markers in postmenopausal women-a randomized controlled study. Nutrients, 10(1), 97. doi:10.3390/nu10010097

  3. Hexsel, D., Zague, V., Schunck, M., Siega, C., et al. Oral supplementation with specific bioactive collagen peptides improves nail growth and reduces symptoms of brittle nails. J. Cosmet Dermatol. 16(4), 520–526. doi:10.1111/jocd.12393

  4. Lupu, M. A., Gradisteanu Pircalabioru, G., Chifiriuc, M. C., Albulescu, R., & Tanase, C. Beneficial effects of food supplements based on hydrolyzed collagen for skin care (Review). Exp. Ther. Med. 20(1), 12–17. doi:10.3892/etm.2019.8342

  5. Shin, J. W., Kwon, S. H., Choi, J. Y., et al. Molecular mechanisms of dermal aging and antiaging approaches. International journal of molecular sciences. 20(9), 2126. doi:10.3390/ijms20092126

  6. Oe, M., Sakai, S., Yoshida, H., Okado, N., Kaneda, H., Masuda, Y., & Urushibata, O. Oral hyaluronan relieves wrinkles: a double-blinded, placebo-controlled study over a 12-week period. Clinical, cosmetic and investigational dermatology, 10, 267–273. doi:10.2147/CCID.S141845

  7. Zdzieblik, D., Brame, J., Oesser, S., Gollhofer, A., & König, D. The influence of specific bioactive collagen peptides on knee joint discomfort in young physically active adults: A randomized controlled trial. Nutrients, 13(2), 523. doi:10.3390/nu13020523

  8. Alcock, R. D., Shaw, G. C., Tee, N., & Burke, L. M. Plasma amino acid concentrations after the ingestion of dairy and collagen proteins, in healthy active males. Frontiers in nutrition, 6, 163. doi:10.3389/fnut.2019.00163

  9. Cooperman T, M.D. Collagen supplements review for skin and joints & top picks.

  10. Proksch, E., Schunck, M., Zague, V., Segger, D., Degwert, J., & Oesser, S. Oral intake of specific bioactive collagen peptides reduces skin wrinkles and increases dermal matrix synthesis. Skin pharmacology and physiology, 27(3), 113–119. doi:10.1159/000355523

  11. U.S. Food & Drug Administration. Additional information about high-intensity sweeteners permitted for use in food in the United States.

  12. Patel, D. P., Swink, S. M., & Castelo-Soccio, L. A review of the use of Biotin for hair loss. Skin appendage disorders, 3(3), 166–169. doi:10.1159/000462981

  13. NIH National Library of Medicine. Biochemistry, collagen synthesis.

  14. NIH National Library of Medicine. Physiology, connective tissue.

  15. Sangsuwan, W., & Asawanonda, P. Four-weeks daily intake of oral collagen hydrolysate results in improved skin elasticity, especially in sun-exposed areas: a randomized, double-blind, placebo-controlled trial. The Journal of dermatological treatment, 32(8), 991–996. doi:10.1080/09546634.2020.1725412

  16. Maia Campos, P., Franco, R., Kakuda, L., Cadioli, G. F., Costa, G., & Bouvret, E. Oral supplementation with hydrolyzed fish cartilage improves the morphological and structural characteristics of the skin: A double-blind, placebo-controlled clinical study. Molecules (Basel, Switzerland), 26(16), 4880. doi:10.3390/molecules26164880

  17. Bolke, L., Schlippe, G., Gerß, J., & Voss, W. A collagen supplement improves skin hydration, elasticity, roughness, and density: Results of a randomized, placebo-controlled, blind study. Nutrients, 11(10), 2494. doi:10.3390/nu11102494

  18. Hexsel, D., Zague, V., Schunck, M., Siega, C., Camozzato, F. O., & Oesser, S. Oral supplementation with specific bioactive collagen peptides improves nail growth and reduces symptoms of brittle nails. Journal of cosmetic dermatology, 16(4), 520–526. doi:10.1111/jocd.12393

  19. Kalman, D. S., & Hewlings, S. The effect of oral hydrolyzed eggshell membrane on the appearance of hair, skin, and nails in healthy middle-aged adults: A randomized double-blind placebo-controlled clinical trial. Journal of cosmetic dermatology, 19(6), 1463–1472. doi:10.1111/jocd.13275

  20. König, D., Oesser, S., Scharla, S., Zdzieblik, D., & Gollhofer, A. Specific collagen peptides improve bone mineral density and bone markers in postmenopausal women-A randomized controlled study. Nutrients, 10(1), 97. doi:10.3390/nu10010097

  21. Lugo, J. P., Saiyed, Z. M., Lau, F. C., Molina, J. P., Pakdaman, M. N., Shamie, A. N., & Udani, J. K. Undenatured type II collagen (UC-II®) for joint support: a randomized, double-blind, placebo-controlled study in healthy volunteers. Journal of the International Society of Sports Nutrition, 10(1), 48. doi:10.1186/1550-2783-10-48

  22. Rasmussen B, Ennis M, Pencharz P, Ball R, et al. Protein requirements of healthy lactating women are higher than the current recommendations. Current Developments in Nutrition, 4(2): 653. doi:10.1093/cdn/nzaa049_046

  23. NIH Office of Dietary Supplements. Vitamin C.

  24. Institute of Medicine. Dietary reference intakes for vitamin A, vitamin K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc. Washington, DC: The National Academies Press. doi:10.17226/10026

  25. Edakkanambeth V, J., Bauer, B. A., & Hurt, R. T. Over-the-counter enzyme supplements: What a clinician needs to know. Mayo Clinic proceedings, 89(9), 1307–1312. doi:10.1016/j.mayocp.2014.05.015

  26. Paul, C., Leser, S., & Oesser, S. Significant amounts of functional collagen peptides can be incorporated in the diet while maintaining indispensable amino acid balance. Nutrients, 11(5), 1079. doi:10.3390/nu11051079