Frediani, B., M. Rossini, S. Adami, G. Bianchi, O. Di Munno, L. Sinigaglia, M. Antonelli, and G. Minisola. 1. “Study of Vitamin D Status of Rheumatoid Arthritis Patients Rationale and Design of a Cross-Sectional Study by the Osteoporosis and Metabolic Bone Diseases Study Group of the Italian Society of Rheumatology (SIR)”. Reumatismo 58 (4), 314-18. https://doi.org/10.4081/reumatismo.2006.314.