Notably, 25(OH)D levels in patients with arthritis and rheumatism were higher than those in the whole group when anemia risk was in the trough, which may be due to the effects of the pathological processes underlying arthritis or rheumatism on anemia, or the regulation of 25(OH)D by PTH; however, neither significantly affected the overall trend relationship between anemia and 25(OH)D. Here, PTH is linked to Arthritis.