Background Vitamin D status varies with geographic location and no studies of vitamin D in systemic lupus erythematosus (SLE) have been reported in the Southern Hemisphere.

Objectives To assess the prevalence of vitamin D deficiency in an Australian SLE cohort, and its relationship with disease activity.

Methods Data were collected prospectively on 119 consecutive patients with SLE in the Monash Lupus Clinic in Melbourne, Australia, between January 2007 and January 2013. Patients had simultaneous serum 25-hydroxyvitamin D concentration and disease activity (SLEDAI-2K) recorded. Statistical methods were used to determine the correlation of serum vitamin D level and disease activity both at baseline and at a subsequent time point. Adjustments were made for the use of glucocorticoids, immunosuppressants and vitamin D supplementation.

Results Vitamin D deficiency (<40 nmol/L) was detected in 27.7% of patients at baseline. Multiple regression analysis showed a significant inverse correlation of SLEDAI-2K with baseline vitamin D level and with vitamin D supplementation. Over a 12-month period of observation, among the 119 patients, there were 464 serial vitamin D measurements with corresponding SLEDAI-2K, representing 266 time intervals. The median change in vitamin D level was an increase of 25 nmol/L and this corresponded with a decline in SLEDAI-2K of 2 units. In regression analysis, there was a significant association between low vitamin D at a prior time point and a rise in SLEDAI-2K at the subsequent time point (univariable OR 3.3, 95% CI 1.5 to 7.7, p=0.005) or having a high disease activity (SLEDAI-2k>10) at the subsequent time point (univariable OR 3.1, 95% CI 1.4 to 6.8, p=0.004).

Conclusions In Australian patients with SLE, low vitamin D was associated with a higher disease activity and an increase in serum vitamin D was associated with reduced disease activity over time. The therapeutic effect of vitamin D in SLE should be further assessed in interventional studies.