CYP26B1 and osteoarthritis: Khosasih et al. showed (28) that vitamin A promotes hand OA by regulating the downstream gene CYP26B1, which breaks down excess retinoic acid, the most active metabolic derivative of vitamin A. Increased expression of CYP26B1 decreases retinoic acid levels, and decreased bioavailability of retinoic acid damages cartilage (29) and aggravates Osteoarthritis.