American Academy of Orthopaedic Surgeons, OrthoInfo: “Articular Cartilage Restoration.”

Arthritis Foundation: “Are Collagen Supplements Helpful for Arthritis?”

Experimental and Therapeutic Medicine: “Beneficial effects of food supplements based on hydrolyzed collagen for skin care (Review).”

Grandview Research: “Collagen Market Growth & Trends.”

Harvard Medical School: “Do retinoids really reduce wrinkles?”

Molecular Cell Biology: “Collagen: The Fibrous Proteins of the Matrix.”

Nancy E. Lane, MD, distinguished professor of medicine, rheumatology, and aging, University of California, Davis.

Nazanin Saedi, MD, associate professor; director, Jefferson Laser Surgery and Cosmetic Dermatology Center.

Nutrients: “A Collagen Supplement Improves Skin Hydration, Elasticity, Roughness, and Density: Results of a Randomized, Placebo-Controlled, Blind Study.”

Penn Medicine: “4 Head-to-Toe Ways That Collagen Can Improve Your Health.”

Rheumatology and Therapy: “Role of Collagen Derivatives in Osteoarthritis and Cartilage Repair: A Systematic Scoping Review With Evidence Mapping.”

Versus Arthritis: “Collagen.”