PTH and Arthritis: In the fully adjusted model including PTH, history of osteoporosis, and number of days with arthritis or rheumatism, the ORs and 95 percent CIs for anemia incidence across the serum 25(OH)D quartiles were 0.771 (0.449, 1.326), 0.499 (0.267, 0.932), and 0.596 (0.323, 1.097), compared with the first quartile of serum 25(OH)D (Supplementary Table 2).