Joint Health Important for Collagen Production Provides Structural Support Vegetarian Formula L-Proline is an amino acid that is essential for the synthesis of collagen, the most abundant protein in mammals. ; Collagen is the main structural protein that constitutes all human connective tissues, including skin, tendons, ligaments, joints, bone, and vasculature (veins and arteries). ; L-Proline therefore provides building blocks that help to stabilize and strengthen the structural components of the body. ; Although proline can be made in the body, low protein and vegetarian diets may not provide optimal support for the production of collagen.* ; NOW L-Proline Vcaps are 100% vegetarian.