Proline and Hydroxyproline: Amino Acids Critical for Collagen Stability


Second only to water in terms of body content is collagen(1). Collagen is the most abundant protein in the body, vital for maintaining the normal structure, strength and function of connective tissue such as bones, skin, cartilage, and blood vessels. It helps skin cells adhere to one another and also gives the skin strength and elasticity. The amino acid precursor proline,(2) along with hydroxyproline, play key roles for collagen stability and therefore are incredibly important in the field of beautification.


Collagen makes up 30% of the body’s protein and 70% of the skin’s protein. It can act as a moisturizer and it serves as a protector and building block of skin.


Skin cell turnover, a vital part of the process of maintaining and regenerating skin to make it beautiful, is encouraged by amino acids.


Collagen contains high amounts of the amino acids glycine, proline, alanine, and hydroxyproline, with smaller amounts of several other amino acids.

  • 33.7% glycine

  • 13.3% proline

  • 11.6% alanine

  • 9.7 % hydroxyproline

  • 31.8% other amino acids

These particular amino acids are critical for keeping skin supple, hair shiny, and nails, bones and joints strong. They perform a function in supporting collagen synthesis.


Amino acid composition of proteins and free amino acids(3) in more mature skin differs significantly from that of younger skin. Amino acids play a key role in water binding to the skin and with a shift in their composition as we age, so too, does the skin’s ability to retain moisture and remain supple.


Collagen’s amino acids are considered “conditionally essential” meaning you can survive without them but once your body is subjected to stress of any kind such as when you are fighting an illness, collagen’s amino acids become essential. Because stress is so much a way of life for most people, these conditionally essential amino acids actually become essential.


Hydroxyproline + Proline

These two amino acids play principle roles in collagen proteins and they function as major extracellular components in connective tissues (e.g., skin, tendon, cartilage, vessels of the vascular system, and bone).


Hydroxyproline and proline form almost one-third of collagen. A small amount of hydroxyproline has been found only in elastin and for this reason, hydroxyproline is used in the investigation of collagen.


Hydroxyproline and proline play key roles for collagen stability. They permit the sharp twisting of the collagen helix composed of three chains wound together in a sort of tight triple helix.


Hydroxyproline and proline help provide stability to the triple-helical structure of collagen by forming hydrogen bonds.


Each chain in the helix is more than 1400 amino acids long. A repeated sequence of three amino acids forms this sturdy structure. Every third amino acid is glycine (the topic of an upcoming blog) while many of the remaining positions in the chain are filled by proline and hydroxyproline.


The conversion of proline to hydroxyproline requires vitamin C (ascorbic acid). A deficiency in vitamin C will result in poor conversion of proline to hydroxyproline. This leads to reduced collagen stability.


Proline and hydroxyproline together are vital for collagen biosynthesis, structure, and strength.


Hydroxyproline “Hydroxyproline is a major component of the protein collagen. Hydroxyproline and proline play key roles for collagen stability. They permit the sharp twisting of the collagen helix. It helps provide stability to the triple-helical structure of collagen by forming hydrogen bonds. Hydroxyproline is found in few proteins other than collagen. The only other mammalian protein which includes hydroxyproline is elastin.” —bionity.com


Years-long studies on hydroxyproline revealed unique benefits for this amino acid precursor as an internal beauty agent. It is shown to enhance the growth of epidermal cells and collagen. A human clinical study has demonstrated that hydroxyproline is effective in improving dry, rough skin.

Nutritional Sources of Hydroxyproline

Proline

The amino acid proline is considered non-essential because it is manufactured by the body. It can also be consumed in complete protein foods. Our need for proline increases as we age or if we are challenged with health conditions.


The benefits of anti-aging proline are many:

  • improves overall health of skin

  • regenerates cartilage

  • forms connective tissue

  • alleviates joint pain

  • repairs skin damage and wounds

  • heals the gut lining

  • ameliorates gut health and nutrient absorption

  • supports metabolism

  • bolsters the immune system

  • improves our antioxidant status

  • protects the cardiovascular system

Nutritional Sources of Proline

  • asparagus

  • rice

  • buckwheat

  • cabbage

  • chives

  • cucumbers

  • garbanzo beans

  • peanuts

  • soy

  • watercress


(1) Type I collagen accounts for about 90% of our body’s collagen. Type 1 collagen supports our skin, tendons, ligaments, bones, joints and muscle health. Type II is more rare, found mainly in cartilage and eyes, and is actually manufactured by the body. Type III collagen, the second most abundant type of collagen in the body is quite similar to Type I and it also is manufactured by the body. It helps restore skin’s elasticity and supports the lymphatic system, liver, uterus and intestines.

(2) Amino acids: a group of organic compounds that form the building blocks of proteins that comprise 75% of the body; they are involved in almost every body function, including growth and development, healing and repair, normal digestion, and energy production.

(3) Free amino acids: amino acids that are not bound to a protein.


Hydroxyproline. National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine, pubchem.ncbi.nlm.nih.gov/compound/hydroxyproline.


Li, Peng and Wu, Guoyao. Roles of Dietary Glycine, Proline, and Hydroxyproline in Collagen Synthesis and Animal Growth. Amino Acids, U.S. National Library of Medicine, pubmed.ncbi.nlm.nih.gov/28929384/.

Axe, Josh. Collagen Diet: A 28-Day Plan for Sustained Weight Loss, Glowing Skin, Great Gut Health and a Younger You. Orion Spring, 2020.


Nutritional Cosmetics: Beauty from Within. United Kingdom, Elsevier Science, 2009.

Hydroxyproline, https://www.bionity.com/en/encyclopedia/Hydroxyproline.html.


Wu G, Bazer FW, Burghardt RC, Johnson GA, Kim SW, Knabe DA, Li P, Li X, McKnight JR, Satterfield MC, Spencer TE. Proline and hydroxyproline metabolism: implications for animal and human nutrition. Amino Acids. 2011 Apr;40(4):1053-63. doi: 10.1007/s00726-010-0715-z. Epub 2010 Aug 10. PMID: 20697752; PMCID: PMC3773366.


Kivirikko, Kari I., and Martti Liesmaa. “Effect of Cortisone and Age on the Hydroxyproline and Proline Concentrations of Blood and Urine in the Rat.” Eje, Bioscientifica Ltd, 1 Apr. 1958, https://eje.bioscientifica.com/view/journals/eje/27/4/acta_27_4_007.xml.