Whether oral collagen or collagen hydrolysate can help increase the content of collagen in the skin, thereby improving the moisture and elasticity of the skin, has been controversial.
This article reviews recent domestic and foreign studies on the effects of collagen (especially oral collagen) on the skin. The results show that oral collagen and its hydrolysate can be quickly absorbed in the form of peptides and targeted by the skin. It can significantly increase the content of collagen in the skin, inhibit the degradation of skin collagen, reduce skin damage, and improve the water content of the skin. It is an effective skin-improving nutrient.
Collagen is widely distributed in human bones, skin, blood vessels, ligaments, cartilage, and other tissues and organs. It is the main structural protein of connective tissue, accounting for 25% to 30% of total animal protein. So far, more than 20 types of collagen have been discovered, of which type I collagen has the highest content, about 90%. In the skin, collagen is distributed in the dermis, the content is about 70%, mainly type I (85%), III, and V .
Collagen is generally regarded as the supporting structure of the dermis. Its mesh structure provides protection and elasticity for the skin. A large amount of water, extracellular matrix, and functional cells are distributed between the fibers. It is an important biochemical reaction site for the skin. Provide moisture and nutrients for the epidermis . Collagen in the dermis can be destroyed by many factors: matrix metalloproteinases (MMP) can degrade it, free radicals can denature it, ultraviolet rays in sunlight can denature collagen , and Maillard reaction can make sugar Glycosine reacts with collagen to form glycosylation products , which turns yellow and loses elasticity.
The collagen fibers in aging skin are significantly more than those in young skin, and the texture is disordered (the normal texture is lost after degradation). The content of collagen in the dermis decreases with age, and it decreases significantly in the abdominal skin of women over 40 and menopause . Insufficient synthesis or excessive destruction of collagen in the dermis will weaken the elasticity of the skin and cause various aging symptoms such as wrinkles, lack of water, and dull luster. Therefore, protecting and replenishing collagen in the dermis is important for beauty and skin care. Supplementing antioxidants such as vitamin C, reducing the intake of carbohydrates, inhibiting MMP activity, and avoiding ultraviolet rays can all help protect the collagen in the skin from loss or promote the synthesis of collagen. Traditionally in China, there is a saying that eating donkey skin (Ejiao), trotters, and chicken feet for beauty and anti-wrinkle. The main ingredient of these foods is collagen.
At the same time, cosmetic oral liquid or collagen powder made from collagen hydrolysate (CH) as the main functional ingredient has been popular in the market in recent years. Sellers believe that it has the effect of increasing skin collagen content, improving skin elasticity, and making skin younger and firmer. However, this claim has been refuted by some nutritionists, who believe that although collagen is very important to the skin, this traditional claim of “what to eat to supplement what” is nonsense, and there is no reliable research evidence to prove oral collagen. Protein and its hydrolysate have the effect of improving the skin, even if the user thinks it is effective, it is mostly a psychological effect.
The main reasons for opposition are: 1) Oral collagen may not be absorbed by the body; 2) Even if it is digested, collagen is first broken down into free amino acids and then absorbed, which is no different from ingesting amino acids in other foods. , Does not mean that collagen has any advantages over other protein sources; 3) Even if collagen is digested and then absorbed, it cannot be guaranteed to reach the skin; 4) Even if it reaches the skin, it cannot be guaranteed to participate in the synthesis of collagen in the skin. . This article reviews the research results of collagen at home and abroad in recent years, and discusses the above-mentioned core issues.
1. Digestion and absorption of collagen (can it be absorbed after eating it?)
Collagen is a kind of collagen that is easily absorbed, and a considerable part of it is directly absorbed into the blood in the form of peptides. Leng Xiangjun et al. (2005), Steffen Oesser (1999) and other studies have shown that the absorption rate of collagen exceeds 95%, even up to 100%, and a considerable part of the protein macromolecules can be directly absorbed by the intestine [6-8], Mari Watanabe- Kamiyama, Muneshige Shimizu, Shin Kamiyama et al. (2010) used 14C labeling to prove that the concentration of collagen hydrolysate in plasma reached the peak within 3 hours after ingesting CH in Winstar mice , all of which indicate collagen hydrolysate Can be digested and absorbed well. Koji Iwai, Takanori Hasegaw (2005), and others studied the absorption of collagen peptides from pig skin, chicken feet and cartilage in the human body. 1-2 hours after oral administration, a large amount of it can be absorbed into the blood, and it is confirmed that a considerable part (1/3 or more) is directly absorbed in the form of peptides, rather than pure free amino acids (FAA)  . Hiroki Ohara, Hitoshi Matsumoto (2007) used fish scales, fish skin, pig skin collagen to conduct absorption studies, confirming the previous results, and found that the most peptide entering the blood is the Pro-Hyp structure, Mari Watanabe-Kamiyama et al. (2010) It was also found that after the mice ingested CH, the Gly-Pro-Hyp tripeptide sequence characteristic of collagen appeared in their plasma .
Based on previous research and his own experiments, Steffen Oesser (1999) believed that protein molecules must be hydrolyzed into free amino acids before they can be absorbed into the blood (Boullin et al. 1973, Mathews and Laster 1965). The statement may need to be revised. Experiments have confirmed that protein macromolecules can be directly absorbed by the intestine, and even maintain their original functions .
2. The distribution of collagen after absorption (can it reach the skin?)
Tests have proved that after being absorbed, collagen and its hydrolysates can reach the skin and be used by the skin and liver. Mari Watanabe-Kamiyama et al. used the radioisotope 14C tracer to study the distribution of the type I collagen CH from chicken feet in the body of mice after absorption. Two to six hours after oral administration, the labeled Gly-Pro-Hyp tripeptide was distributed to all major organs of the body. After 14 days, only 70% of the radiation level remained in the skin. The mouse skin was hydrolyzed and analyzed, and it was confirmed that the Gly-Pro-Hyp tripeptide in the skin was a tripeptide from chicken feet . Oesser et al. reported that macromolecular collagen can be directly absorbed and accumulated in the kidney and cartilage . Mari Watanabe-Kamiyama et al. also found that Gly-Pro-Hyp specifically precipitates in the skin. The above experiments show that although type I collagen hydrolysate is initially distributed throughout the body after being absorbed, it can be targeted to be distributed in collagen-rich tissues (including skin) and be specifically utilized.
3. The effect of oral collagen and CH on the skin
3.1 Oral collagen promotes dermal collagen fiber synthesis and fibroblast (FB) proliferation
Naoyamatsuda, Yoh-ichi Koyam et al. (2006) studied the effect of oral collagen on fibroblasts and dermal interstitium. Feeding pigs with collagen polypeptide 0.2g/kg for 62 days, experiments show that oral collagen can increase the density of fibroblasts and promote the formation of dermal collagen fibers in a specific protein manner . Naoya matsuda, Yoh-ichi Koyam and others have also reported experiments on feeding collagen hydrolysate to increase the diameter and density of collagen fibers in rabbit Achilles tendons. Experiments have shown that orally absorbed collagen can specifically act on collagen fibers in tissues rich in collagen, such as Achilles tendon and dermis .
3.2 The effect of oral collagen on the skin
Sumida (2004) evaluated the effect of daily intake of CH (10g) on the skin through experiments. The test group consisted of 20 healthy Japanese women, and the control group consisted of 19 people who took a placebo. In the 60 days of the test, it was found that the water absorption capacity of the skin of women in the test group gradually increased, but compared with the control group, the statistical difference was not significant enough. It is worth emphasizing that both groups took 400mg of vitamin C, so the synthesis effect of collagen can be considered to be brought by vitamin C, but this is a two-factor test, and the dose of Vc taken is very large, and it is not Deny the improvement effect of collagen on the skin. Koyama Yoichi et al. (2006) studied the effect of daily intake of collagen peptides (CP) on the water-holding capacity of the human stratum corneum. The healthy Japanese women in the test group drank 100ml of beverage containing 10g CP per day for 60 days. The skin stratum corneum water absorption capacity of 20 women in the test group was higher than that in the control group (take a placebo), and no abnormal blood tests were found. It is suggested that oral CP can increase the water content of the stratum corneum without causing blood abnormalities . Yasutaka Shigemura (2009) et al. studied the effect of Pro-Hyp oligopeptides derived from collagen on the migration and growth of fibroblasts in mouse skin. The test results suggest that Pro-Hyp may stimulate the growth of fibroblasts in the skin and increase the number of fibroblasts that migrate from the skin . Oral collagen can inhibit skin damage caused by UVB. Modori Tanaka et al. (2009) conducted a 6-week experiment. The experimental group fed mice with 0.2g/kg/day collagen peptide (CP) and found that oral CP can significantly increase the water content of the stratum corneum and prevent the stratum corneum. It thickened due to UVB irradiation and increased the content of type I collagen in the dermis of mice (nearly 2.5 times higher than the control group). This may be due to the antioxidant effect of collagen peptides, but it may also be due to other activities . Hiroki Ohara et al. (2010) used cultured human skin fibroblasts as materials to study the effects of various CPs on skin extracellular matrix components and cell proliferation, and found that Pro-Hyp at a concentration of 200nmol/mL increased fibroblasts Proliferation (1.5 times) and hyaluronic acid synthesis (3.8 times), the author believes that CP can stimulate cell mitosis and hyaluronic acid synthesis . VivianZague et al. (2011) studied the effect of daily intake of collagen hydrolysate (CH) on skin extracellular matrix proteins. The type I collagen in the skin of mice in the test group increased by 4 times (3.4±1.7), while the control group fed with casein only had (0.8±0.5). Type IV collagen, the test group is (6.7±1.1), which is 3 times (2.3±1.2) of the control group. The author believes that CH is not highly regarded in nutrition (incomplete amino acids), but it can significantly promote the synthesis of type I collagen. But for human skin effects, clinical research is still needed . Yu Zhou, Fan Qingsheng et al. (2010) observed the effect of collagen extracted from fish skin on human skin moisture and general safety, and the test concluded that oral fish collagen can significantly improve skin moisture . Zhou Shuanglin, Wang Haiyan and others (2011) observed the effectiveness and safety of small-molecule fish collagen powder in improving female facial skin. Analyze the skin with questionnaire survey, Visia, skin moisture tester, etc. The results of the questionnaire survey showed that oral administration of small molecule fish collagen powder has the effect of improving sleep and strengthening physical strength, and the health score of the test group was significantly improved compared with that before oral administration (P<0.05). The instrument test showed that the facial skin fine lines, pores, texture, purple matter, moisture, and oil of the test group improved significantly (P<0.05) (the self-experience of the test users was consistent with the trend of the instrument test results). The volunteers had no obvious adverse reactions before and after the test. It is concluded that oral small-molecule fish collagen powder can improve the facial skin texture of women to a certain extent, without obvious adverse reactions, and has good safety and effectiveness .
4. Discussion and Outlook
4.1 The mechanism by which oral collagen and CH can specifically increase the collagen content in the skin
As mentioned above, existing trials have confirmed that oral collagen and CH/CP can increase the collagen content in the skin, thereby improving skin moisture content and reducing skin damage caused by UVB. The mechanism may be: to provide the skin with enough amino acids needed to synthesize collagen as raw materials, and a considerable part of it is directly and efficiently absorbed and utilized in the form of active small peptides. At the same time, collagen peptides can resist oxidation and inhibit MMP2 is active, thereby protecting the collagen in the skin from consumption and decomposition.
4.1.1 Oral collagen and CH can effectively supplement the amino acids needed for skin synthesis of collagen
The amino acid composition ratio of collagen is very special. The content of glycine and proline-hydroxyproline is about 50%. The amount of these three amino acids that can be provided by ordinary protein food is far from enough. Assuming that an adult synthesizes 10g of collagen every day, it needs about 2.5g of proline/hydroxyproline, assuming that the absorption rate of food is 100%, and using the amino acids provided by eggs as raw materials, enough proline/hydroxyproline will be obtained (The content of proline in eggs is 3.07% ), a total of 943g is needed, about 19 eggs. However, if collagen or CH is used to supply these amino acids, only 10g is enough. This shows that oral collagen is highly effective. Indeed, glycine and proline are not traditionally essential amino acids for the human body, and can be synthesized from other amino acids, but this raises two questions:
1) Tyrosine, cysteine, together with glutamine, arginine, and possibly glycine and proline are called conditionally essential amino acids, because they are synthesized under specific physiological and pathological conditions. The speed cannot meet the needs of cells . When the human body is aging, due to many factors such as free radicals, endogenous aging factors, glycosylation, photoaging, MMP activity, etc., the synthesis slows down and the loss increases. The conditional essential amino acids needed to synthesize collagen may be in short supply. Need special supplement.
2) Even if the essential amino acid intake is sufficient, it can be converted into these amino acids, but other nitrogen sources must be obtained, which is an energy-consuming process. Experiments have confirmed that relying only on essential amino acids or a high proportion of essential amino acids cannot make the experimental animals grow well. In 1965, the expert group of FAO and WHO proposed: “The proportion of non-essential amino acids in the diet, and therefore the ratio of all essential amino acids to total nitrogen in the diet in grams, has a significant impact on the need for essential amino acids.” 
For the body, the use of amino acids and peptides that can be directly used is the lowest energy consumption and fastest way. This is likely to be an important mechanism for oral collagen to have a high-efficiency effect on the skin and other collagen-rich connective tissues. one.
4.1.2 Oral collagen and CH have an efficient way and way of absorption-direct absorption of peptides
It is generally believed that protein must be hydrolyzed into free amino acids (FAA) in the small intestine before it can be absorbed and used by the body. This is the fundamental reason why some people believe that oral intake of collagen is no different from other types of protein.
However, it is not. The aforementioned literature has mentioned that the peptide structure derived from oral collagen and CH has a peak in plasma 2 hours after oral intake, and the original sequence structure is still maintained when transported to the skin.
Zhang Wei and Liao Yiping pointed out: Because of the view that Dogman’s protein must be digested into FAA to be absorbed, peptide research has been at a standstill.
Bachwell (1995) found that there is an oligopeptide transport system with glycylproline on the brush border of the intestine. The research of Grimble et al. (1986) showed that the human body has a great ability to hydrolyze peptides. A large number of small peptides can pass through the intestinal barrier and enter the blood circulation in the form of small peptides. Studies on animals have concluded that small peptides can be dipeptide after being completely absorbed. , The form of tripeptide enters the blood circulation. The absorption of peptide is not only faster than free FAA, but also has the advantage of high absorption rate. In-fante (1992) and Boza (1995) confirmed that when oligopeptides were used as the nitrogen source, the overall protein deposition was higher than the corresponding AA diets or intact protein diets. Peptide is not only a substrate of protein metabolism, but also an important regulator of physiological activity. It can directly act as a neurotransmitter and indirectly stimulate the secretion of intestinal receptor hormones or enzymes to play a physiological role .
In the research work on the amino acid requirements of livestock and poultry, it was also found that the selected feed sources of the basic diets are different, and the results of the amino acid requirements obtained are very different. The reason is that the amino acid utilization rate in different feeds is different (Jicheng, etc., 1984). As for why there are differences in the amino acid utilization rate of feeds from different sources, researchers have been evading it as a black box theory .
Studies have confirmed that peptides can be directly absorbed, have an independent transport mechanism, and have a higher absorption efficiency than FAA. This black box theory should be able to explain this black box theory, and the same is true for oral collagen absorption.
4.2.3 Collagen peptides can be directly used by skin tissues more efficiently
Traditionally, it is believed that protein synthesis begins with the transfer of FAA from tRNA to mRNA assembly. On mRNA, FAA is arranged in sequence according to the genetic code to form a peptide chain, which then forms a high-level structure . Backwell (1994) used isotope techniques to confirm that the tissue itself has the ability to directly use peptides to synthesize milk protein. Le Guowei et al. also found through animal experiments that peptides can be directly used by tissues, which is more efficient than FAA . It is known that in the process of classical protein synthesis, every time an AA is assembled to form a peptide bond, a total of 4 high-energy phosphate bonds are consumed . But if peptides can be used directly, it is an energy-saving and faster process. Different protein sources can hydrolyze different peptides . It can be guessed that oral collagen and CH can provide peptides that are more suitable for the body to synthesize its own collagen efficiently and energy-savingly, thus having advantages over other protein sources or FAA (ie. : With protein specificity ).
4.4.4 CP promotes other mechanisms of skin collagen (chemokinesis, signal transduction, anti-oxidation, and inhibition of MMP)
Studies have found that after oral administration of collagen and CH/CP can specifically act on collagen-rich tissues, and different amino acid sequences of peptides are enriched in different locations: Gly-Pro-Hyp sequences are mainly used by the skin [8, 11].
This may be related to the chemotaxis between fibroblasts and collagen peptides. In vitro cell culture experiments have found that Pro-Hyp has chemotaxis to fibroblasts, peripheral blood neutrophils, and monocytes [24,25]. Studies by Yasutaka Shigemura (2009) have repeatedly confirmed this phenomenon: Pro-Hyp can significantly accelerate the migration of fibroblasts from the skin to the culture plate . Yasutaka Shigemura et al. believe that Pro-Hyp may be an important physiological role in both normal and pathological conditions. It may act as a signal peptide in the Pro-Hyp signaling pathway, and even be directly transported into fibroblasts as a direct signal . The positive effect of oral collagen and CH on collagen in skin tissues may also come from its antioxidant effect and inhibiting MMPs, preventing collagen in the body from being decomposed and destroyed. The research of Liu Gaomei (2012) shows that small molecule collagen peptides have significant antioxidant effects .
Wang Jieyun (2009) found that high-dose collagen peptides can significantly improve the total antioxidant capacity, superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and peroxide in the blood and skin of model mice. Physical enzyme activity (CAT) activity (P<0.05), significantly reduces the total free radical (ROS) level and malondialdehyde (MDA) content in the body, and the effect is slightly better than 0.1% lipoic acid (LA) .
Active MMPs is one of the main causes of collagen loss. Vivian Zague’s experiment showed that the intake of CH significantly reduced the activity of MMP2 and its zymogen (P<0.05). The I that this MMP is mainly responsible for decomposition is the main collagen of the dermis-type I collagen. .
4.2 Future Outlook
Oral collagen and CH have good effects and safety. This is one of the most important foundations for it as a skin care product. Clinical studies have shown that CH is well tolerated [28-30]. No side effects or toxic reactions were observed in mice oral or skin acute toxicity tests [12,31]. Research on its effects on different strains of Salmonella, Escherichia coli (E. coli), and bone marrow cells did not show any increase in mutations or carcinogenicity . All available data clearly show that oral CH is safe for both short-term and long-term oral administration. As a kind of food, FDA lists CH as GRAS (gernerally recognized as safe), which is the highest level of safety . The German Federal Institute of Medicines and Medical Devices, Ministry for Consumer Affaires, and WHO have also confirmed that CH is safe, and there is no safety risk in large quantities or in general consumption. Yu Zhou, Fan Qingsheng (2010) observed the general safety effects of oral fish skin collagen on the human body, and showed that fish collagen has no obvious damage to human health. The results of electrocardiogram, abdominal ultrasound, chest examination, etc. are all within the normal range. .
The mechanism of action of collagen and CH is not yet fully understood, and clinical studies on humans are not yet widespread. Obviously, there is still a lot of work to be done in this regard. However, existing research has clearly pointed out the direction and trend.
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