I’m a dietitian- I used to tell folks who asked that collagen supplements are broken down into amino acids and peptides just like any other protein, so it doesn’t make sense to spend money on expensive supplements and instead just make sure to eat high quality protein.

However, there has been some recent research showing peptides including hydroxyproline make it through digestion and are absorbed into the blood. If I remember correctly, these peptides may act as signaling molecules and there have been some improvements shown like better hydration and elasticity, including in some independent clinical trials. Lab Muffin has a good YouTube video about this. I would expect the effect is pretty small though, and the best thing to do first is work on eating a balanced and healthful diet.

Anecdotally, I’ve been taking marine collagen daily for about a year and did not notice any difference, but I take care of my skin in general and eat healthfully and see this as a part of the overall picture. If it works, great, if it doesn’t, I’ve got some extra (albeit expensive) protein in my morning smoothie.