Vitamin D level: is it related to disease activity in inflammatory joint disease?

The objectives of this study are to assess the vitamin D status in patients (pts) with inflammatory joint diseases (IJD), and its correlation with disease activity. 121 consecutive pts (85 rheumatoid arthritis (RA), 22 psoriatic arthritis (PSA), 14 ankylosing spondylitis (AS)) underwent clinical and laboratory evaluation which included kidney and liver function tests, serum calcium and phosphor levels, 25(OH)D and parathyroid hormone (PTH). Disease activity was assessed by DAS 28 in RA and PSA pts and by BASDAI in AS pts, sedimentation rate (ESR) and CRP. According to activity indexes, pts were divided into subgroups with low (DAS28 < 3.2 and BASDAI < 4), and moderate-to-high disease activity (DAS28 > 3.2 and BASDAI > 4). Associations between serum levels of 25(OH)D and age, gender, ethnicity, type and disease duration, treatment, (anti-tumor necrosis factorα (TNFα) agents or DMARDs), seasonal variations, and disease activity were assessed. Vitamin D deficiency was found in 51 pts (42.1%). The incidence was higher among Arab pts (76.7%) compared to Jews (23%). The difference of 25(OH)D levels between Arabs (mean 9.4 ± 4.2 ng/ml) and Jews (mean 17.8 ± 8.4 ng/ml) was statistically significant (p < 0.0001). We did not find correlation between vitamin D levels and the other evaluated factors. A surprisingly high incidence of vitamin D deficiency was found in IJD patients in a sunny Mediterranean country. This finding justifies the inclusion of vitamin D in the routine lab work-up of pts with IJD. The only statistical significant correlation was found between vitamin D level and ethnic origin. Further studies are needed to look for genetic polymorphism of vitamin D receptors.