The etiology of osteoporosis associated with rheumatoid arthritis (RA)
is unknown. We studied the calcium and vitamin D metabolism in 143 wo
men with RA (mean age 50.7 years). Albumin corrected serum calcium was
normal. Serum alkaline phosphatase was increased in 29 percent of cas
es. Serum vitamin D levels were frequently very low. In 16 percent of
the RA patients serum 25(OH)D concentration was below 12.5 nmol/L, whi
ch is arbitrarily considered as the limit of vitamin D deficiency oste
omalacia. In the winter season 73 percent of the patients had serum 1,
25(OH)2D levels below the seasonally adjusted normal range. The lowest
values were found in patients with high disease activity. We suggest
that there is a disturbance in vitamin D metabolism in RA. This might
play a role in osteoporosis associated with RA.