Collagen seems to be another frequent supplement I get asked about . Collagen is found in connective tissue and can be used during exercise routines but also in the prevention and treatment of wrinkles as well as to strengthen hair I believe.
There are no studies on passage into breastmilk and it would therefore be unethical for me to comment.
Elactancia however, designates it as very low risk:
“A fibrous-protein type which is a component of the mammalian connective tissue forming the attachment fibers of all tissues in the organism (bone, cartilage, tendons, skin, muscles, etc.). It represents one-third of total body’s protein content and is composed by amino acids.
Collagen has a great variety of medical, surgical, nutritional and industrial uses such as grafts, sutures, hemostatic products, subcutaneous implants and fillers, pill and capsule covering, glue and cement manufacturing, parts of musical instrument, cosmetic gels, food, photographic and pharmaceutical industry.
Collagen, because of its fibrous nature, is very difficult to chew and digest. To be used as a food it needs to be boiled and treated with various chemicals that break down the bonds and convert it into the so-called hydrolyzed, denatured collagen or gelatin, which is marketed as powder or tablets for various medicinal or health uses like arthritis, joint pains, weight loosing, anti-aging, strengthening of the hair or nails, improvement of the physical fitness and so on, all of them without any serious scientific basis that would guarantee effectiveness.(MedlinePlus Supplements 2015, Revenga 2015, EFSA 2013, EFSA 2011)
Since the last update we have not found any published data on its excretion in breast milk.
Because of a protein nature it is digested by the gastrointestinal tract and absorbed itself as a form of amino acids as those of any other meat. This prevents both the passage to breast milk as a hypothetical plasma absorption by the nursing infant.
Collagen as a supplement is not necessary at all whenever a healthy and balanced diet is followed. https://juanrevenga.com/2015/09/diga-colage-no-o-la-tonteria-de-los-suplementos-de-este-tipo/”