Hydroxyproline is one of four amino acids that are the main components of the protein collagen. Amino acids are the building blocks of proteins. Collagen consists of hydroxyproline, proline, lysine, and glycine. There are around 20 different types of collagen in the body. Depending on where it is located, collagen can appear as a gel-like substance or as a tightly-packed bundle of fibers. No matter where it occurs, collagen requires hydroxyproline to support its intertwined triple helix structure. Hydroxyproline is essential for the stability of the collagen molecule. Hydroxyproline is considered a non-essential amino acid because it need not form part of a healthy diet. The body is able to synthesize hydroxyproline from other components.
Hydroxyproline is formed through hydroxylation of the amino acid proline in the gastrointestinal tract. During this process, a bonded oxygen-hydrogen molecule attaches to the carbon atom in the proline amino acid. This hydroxylation process requires the presence of vitamin C (ascorbic acid) which is considered an essential vitamin because the body cannot produce it. Vitamin C must be ingested either as an oral supplement or as part of a healthy diet. Vitamin C is found in many fruit and vegetables, such as peppers, tomatoes, potatoes, strawberries, kiwi fruit, and citrus fruits. Vitamin C is water soluble and cannot be stored in the body. It is, therefore, essential to consume sufficient quantities of vitamin C on a daily basis. According to the Mayo Clinic, adult men should consume at least 90mg of vitamin C each day. The recommended daily intake for women is normally 75mg, though pregnant women may require 85mg per day. Women who are breastfeeding should consume 120mg of vitamin C each day.
A lack of vitamin C in the body causes scurvy. The symptoms of scurvy include gum disease, spots, bruising, and wounds that will not heal correctly. These symptoms result from decreased hydroxylation of proline, leading to a deficiency of hydroxyproline, which makes the collagen molecule unstable. While scurvy can be fatal if left untreated, it rarely reaches such serious stages in modern times. Scurvy is easily treated simply by ingesting vitamin C.
To promote collagen production through the diet, a study published in the Journal of Cardiovascular Pharmacology in 2007 recommended combining foods rich in lysine (eggs, tomatoes, animal protein, dairy products, nuts, and seeds), proline (egg whites and wheatgerm), and vitamin C with green tea.
The protein collagen is a vital component of the subcutaneous matrix, the connective tissue that supports the skin. Collagen helps to heal wounds and rebuild the skin. The skin is constantly renewing itself and collagen is a vital part of the skin's natural regenerative processes. As part of the aging process, collagen breaks down. This leads to sagging skin and the formation of wrinkles. Healthy levels of hydroxyproline in the body support the stability of collagen, helping skin remain firm, toned, and flexible.
Topical application of hydroxyproline can improve the condition of the skin, helping it appear more youthful. For this reason hydroxyproline is found as an ingredient in anti-aging skin creams, serums, and other skin products. Hydroxyproline can also improve the appearance of skin damaged by stretch marks. When applied topically to the skin, hydroxyproline penetrates the outer layers of the skin and supports collagen and elastin production in the subcutaneous matrix. Topically applied hydroxyproline also supports the production of epidermal keratinocytes, which are the main cells in the skin's outer layers. Hydroxyproline also hydrates the skin by boosting production of ceramides, a type of lipid molecule. Ceramides prevent the loss of moisture from skin cells.
Hydroxyproline also inhibits the production of elastase enzymes, which contribute to the aging process by breaking down vital elastin in the subcutaneous matrix.
Tablets containing a derivative of hydroxyproline, N-acetyl-L-hydroxyproline, reduce the inflammation and swelling caused by osteoarthritis.
Research is underway to determine whether compounds from the 4-cis-hydroxyproline group may be useful in the development of a skin whitening agent. The concept is that the product would inhibit the production of melanin or inhibit melanocyte differentiation. This type of skin whitening product could address pigmentation abnormalities that occur in the form of chloasma and sun spots. While clinical research indicates a possible use for hydroxyproline in skin whitening, these products are still in the very early stages of development.