- A case-control study of serum tocopherol levels and the alpha- to gamma-tocopherol ratio in radiographic knee osteoarthritis: the Johnston County Osteoarthritis Project. Jordan, J.M., De Roos, A.J., Renner, J.B., Luta, G., Cohen, A., Craft, N., Helmick, C.G., Hochberg, M.C., Arab, L. Am. J. Epidemiol. (2004)