"Collagen is the most abundant structural protein found in the mammalian body, accounting for approx. 25% of the total protein."(1) Over 20 collagen types in the body(2) giving flexibility and strength in "skin, nails, muscles, joints and bones." There are 3 more abundant types but 90% of the body's collagen is type I, found in "various body parts such as skin, tendon, vascular ligature, organs, bone, etc."(1) Drinking adequate water is vital to hydrate the body, however, type I collagen (the major type in skin) has been shown to be another major factor in the skin's ability to hold water (needed for skin's elasticity)(2). Type II is the big type in cartilage and is "also found in vertebral disks, inner ear and the vitreous."(1)
The body produces collagen, but produces less with age(2). "Some bacteria and viruses... smoking, autoimmune disorders, sunlight, high sugar consumption, etc." all break down collagen(1). Supplementing thus becomes more and more key with age to help support "healthy skin, joints, and bones". Foods have collagen in long fibers(2) (That's the form they take when they build up an animal body)(1) that the body can't digest very well. Enzymes break them down into shorter peptide pieces ready for transport and use. [Peptide/hydrolyzed form is thus especially key!] NOTE: Synthesis of collagen requires Vitamin C as it is need for the production of "hydroxyproline amino acids in the collagen fibril."(1)
Marine collagen (again, get peptides!) comes from collagen-rich "skin, bones, and scales of cold-water fish" that are a major part of the three-quarters of the body weights of fish already discarded by the seafood industry [Make sure it's from a non-polluted source tested for impurities!]. It thus is a really good use for a prevalent waste product and thus can be done sustainably. It's also mostly type I(2) [Again, that's the type that forms the vast majority of the body's collagen, and especially in the skin!] Bovine-sourced collagen has type III as well as type I and so helps provide support to some other parts of the body [Get grass-fed!], though in skin, marine collagen is still best. However, for those with sensitivities to fish, [good] bovine collagen may be better(2).
Personal Product Favorites (LINKS):
Tasty Type I marine collagen with Vitamin C and more
Type II collagen with joint health and muscle recovery support
Grass-fed Type III bovine collagen bone broth with Vitamin C
References:
1. Samanthi. "Difference Between Type 1 and 2 Collagen." Difference Between.com. Difference Between. March 10, 2017. Web. January 20, 2021. https://www.differencebetween.com/difference-between-type-1-and-vs-2-collagen/.
2. "Which Collagen Is Right for You?" Isagenix Health. Isagenix Worldwide, Inc. Web. January 20, 2021. https://www.isagenixhealth.net/which-collagen-is-right-for-you/.