Objectives: Patients with systemic lupus erythematosus (SLE) are prone to hypo-vitaminosis D because of their photosensitivity. Vitamin D (vit.D) has beneficial effects not only on bone metabolism but also on the function of the immune system. The relationship between SLE disease activity and vit.D status is controversial and little is known on the effects of current supplementation strategies given for osteoporosis in raising vit.D levels.
Methods: Vit.D levels were measured longitudinally in 50 SLE patients from Northern Italy at two time-points (winter and summer) during disease remission. Thirty patients were also evaluated during a flare. As controls, 170 healthy donors were enrolled. All the samples were analysed for 25-OH vit.D levels by a chemiluminescence assay (DiaSorin SpA, Italy).
Results: SLE patients had lower vit.D levels than controls in the summer (median 29.4 vs. 39.2 ng/ml, p=0.005) but not in the winter (26.4 vs. 21.6 ng/ml). During wintertime, 36 SLE patients were supplemented with vit.D drops (n=24; 48%), vit.D+calcium tablets (n=12; 24%), while 14 (28%) received no supplementation. Patients on oral drops had significantly higher vit.D levels than patients on tablets. The median weekly dosage was higher for oral drops than for tablets (6250 vs. 4560 UI, p=0.009). Winter flares were associated with lower vit.D levels in comparison with remission during the same season for each patient (21.1 vs. 30 ng/ml).
Conclusions: Current strategies of vit.D supplementation seem to be not sufficient for reaching an optimal vit.D status in Italian SLE patients. Vit.D and calcium tablets were less effective, probably because of lower vit.D content and poorer compliance. Vit.D insufficiency detected in the wintertime can be either a predisposing factor for flare or the consequence of the flare itself in SLE patients.