The effect of serum 25-hydroxycalciferol [25(OH)D] on rheumatoid arthritis (RA) activity remains controversial. This study was undertaken with an aim to clarify the relationship between serum 25(OH)D and RA activity, and to determine the effects of dietary vitamin D intake and age on serum 25(OH)D level.
A total of 208 outpatients with RA were matched according to age and sex with 205 individuals without RA (controls) from the TOMORROW study (UMIN000003876). We excluded 27 patients with RA and 19 control subjects who had been prescribed vitamin D medication or were taking vitamin D supplements. Vitamin D intake was assessed in the remaining 181 patients and 186 controls using the brief-type dietary history questionnaire. Serum 25(OH)D levels were measured using a radioimmunoassay.
Serum 25(OH)D levels were significantly lower in patients with RA than in the controls (p < 0.001). There was a significant and positive correlation between age and 25(OH)D in the patients (r = 0.283, p < 0.001), as with vitamin D intake and 25(OH)D, even after adjusting for age (r = 0.313, p < 0.001). Disease activity and 25(OH)D did not significantly correlate.
Patients with RA were observed to have serum 25(OH)D levels which correlated with vitamin D intake and age but not disease activity.