Background Low 25-OH Vitamin D is associated with SLE. Both a randomized clinical trial and a longitudinal cohort study proved that supplementation reduced SLE disease activity.
Objectives We examined whether Vitamin D benefits in SLE are dependent on the organ system.
Methods Vitamin D and SLEDAI components were measured at each cohort visit starting in 2010 and 16,519 visits of 1,345 different patients were included. The patients were 92% female, 50% Caucasian, 41% African American.
Organ-specific disease activity was defined as a set of binary variables based on SLEDAI. If the patient received any score for any component, then the patient was defined as having that type of activity.
Interestingly, after adjustment for repeated measures and covariates, the relationship between vitamin D and immunologic disease activity totally disappeared. However, for skin activity, there was a significantly elevated risk among those in the very extreme levels of vitamin D. For Renal Disease Activity, there was a significantly higher rate of renal disease activity among those with low levels of vitamin D. In addition, there was a clear trend such that the higher the vitamin D, the lower the risk of renal disease activity.
We then conducted a “within person” analysis. In this analysis, each person serves as his own control, and the question is: “When a person has a vitamin D level lower than his/her average, are they more likely to have renal disease activity”. Note, this analysis implicitly adjusts for race, sex, and all variables (measured and unmeasured) that are invariant within a person. The results are shown in Table 2.
For Renal, it appears (based on the within-person analysis), that increasing vitamin D results in a reduction in renal activity. Based on other analyses, it is clear this drop was mostly among those in the vitamin D deficiency range.
Conclusions Low vitamin D is associated with cutaneous and renal SLE activity, but not with immunologic (low C3 or high anti-DNA) activity, in adjusted analyses.
Disclosure of Interest None declared