Treatment of Hypovitaminosis D in Rheumatoid Arthritis

Osteoporosis is twice as common in people with rheumatoid arthritis (RA), compared to age and gender-matched controls [1, 2]. Hypovitaminosis D can contribute to osteoporosis pathogenesis by decreasing calcium absorption, leading to a decline in serum ionized calcium, a rise in parathyroid hormone levels and upregulation of osteoclast activity, leading to loss of calcium from the skeleton. Hypovitaminosis D is also common in patients with rheumatoid arthritis [3-5], making it an appealing target to potentially improve health in both RA and osteoporosis.

Vitamin D has theoretic potential to modulate RA disease activity, based on the presence of vitamin D receptors in lymphocytes, macrophages, chondrocytes, and synovial cells [6]. Vitamin D, given as the bioactive metabolite 1,25(OH)2D, ameliorates disease activity in murine models of RA [7, 8]. However, few studies have evaluated the effect of vitamin D on RA disease activity in humans. Two three month open-label studies reported that vitamin D reduced RA disease activity [9] and pain levels [10]. By contrast, an eight-week open-label study [11] reported no reduction in swollen joint counts, inflammatory markers or cytokine levels after vitamin D therapy. The only double-blind, placebo-controlled trial published thus far [12] found no significant effect of vitamin D on RA disease activity, but was limited by the lack of hypovitaminosis D as a criterion for study entry. Indeed, at baseline subjects' mean 25(OH)D levels indicated vitamin D repletion, potentially explaining the null effect of vitamin D on RA disease activity.

Three studies have evaluated the effect of vitamin D on bone mineral density (BMD) in patients with RA [13-15]. Researchers [14] randomized 96 subjects with RA to vitamin D (500 IU/day) and calcium (1000 mg/day) or placebo for two years; vitamin D and calcium therapy modestly increased BMD in the spine and hip. In another study [15], 20 subjects randomized to daily calcium and 1 α-hydroxyvitamin D for up to 24 months experienced similar declines in radius and spine BMD compared to 15 controls [15]. Likewise, vitamin D and calcium did not prevent bone loss in a prospective cohort study of patients with RA [13]. However, none of the studies required hypovitaminosis D as an entry criterion, vitamin D repletion to 25(OH)D levels > 32 ng/ml were not evaluated [13, 14] or achieved [15], and low doses of vitamin D were administered, potentially limiting skeletal benefits of this therapy.

We hypothesized that correction of hypovitaminosis D in subjects with RA would decrease parathyroid hormone (PTH), increase BMD, improve functional capacity and down-regulate inflammatory cytokine production, thereby diminishing disease activity. Vitamin D is inexpensive and widely available. If proven beneficial, vitamin D might become a mainstay of therapy for subjects with RA.