Effect of vitamin D on serum markers of bone turnover in SLE in a randomised controlled trial

Bone health in SLE is adversely affected by vitamin D deficiency, inflammatory cytokines and glucocorticoid use. We hypothesised that vitamin D supplementation would increase markers of bone formation and decrease markers of bone resorption in SLE subjects.

We studied 43 vitamin D-deficient SLE subjects who participated in a 12-week randomised controlled trial of 2000-4000 IU/day vitamin D supplementation versus placebo. Subjects had inactive SLE (SLE Disease Activity Index ≤4) and were taking <20 mg prednisone daily at baseline. We assayed baseline and week 12 serum 25-hydroxyvitamin D, N-terminal propeptide of type 1 collagen (P1NP) and C-telopeptide (CTX). We tested the effect of vitamin D versus placebo on change (Δ) in P1NP and ΔCTX in an intention-to-treat analysis. Secondary analyses evaluated whether vitamin D affected bone turnover among subjects achieving vitamin D repletion (≥30 ng/mL) or currently taking glucocorticoids.

28 subjects were randomised to vitamin D and 15 to placebo. Mean age was 39 years and 40% were using glucocorticoids at enrolment. Repletion was achieved by 46% in the vitamin D group versus none in the placebo group. Changes in bone turnover markers were not significantly different in the vitamin D group versus placebo group (median ΔP1NP -0.2 vitamin D group vs -1.1 placebo group (p=0.83); median ΔCTX +3.5 vitamin D group vs -37.0 placebo group (p=0.50)). The effect of vitamin D did not differ based on achieving vitamin D repletion or baseline glucocorticoid use.

Vitamin D supplementation did not affect the 12-week change in bone turnover markers among SLE subjects in this trial.