Daily dose of 5 g hydrolysed collagen with 80 mg of vitamin C (CP product) and their combination with 30 mg of hyaluronic acid were tested. All improved the skin condition, but hyaluronic acid didn’t show advantage over collagen alone.

The Effects of Dietary Supplementation with Collagen and Vitamin C and Their Combination with Hyaluronic Acid on Skin Density, Texture and Other Parameters: A Randomised, Double-Blind, Placebo-Controlled Trial