Other supplements and dietary factors, such as vitamin C, avocado soybean unsaponifiable, and fatty acid intake, may help treat knee OA. The progression of OA is thought to involve damage by free radicals. The antioxidant properties of these supplements may help quell intra-articular inflammation if increased in the diet.
However, clinical studies have shown minimal gains. While one study reported that higher amounts of vitamin C intake lowered the incidence of knee OA by 11% with no effect on progression, other studies have found no association. Daily doses of 300 mg or more of avocado soybean unsaponifiable may decrease NSAID and analgesic intake by more than half, with similar efficacy to 400 mg chondroitin sulfate 3 times daily after 6 months.
Omega-3 polyunsaturated fatty acid plasma levels have an inverse association with patellofemoral cartilage loss. Omega-6 polyunsaturated fatty acid plasma levels are associated with synovitis. Increased consumption of saturated fatty acids may increase bone marrow lesions in the knee.
Overall, the benefits of these supplements and dietary factors are dubious and should not be the focus of knee OA treatment.