Objectives: Several reports have indicated an association between systemic lupus erythematosus (SLE) and low levels of vitamin D. We examined several blood work parameters in SLE patients and controls and performed an extensive data analysis in order to investigate the links between blood levels of calcium, vitamin D, and SLE disease.
Methods: 4,278 SLE patients and 16,443 age and sex-matched controls were selected from a national health insurer database in Israel. Patients with no blood work results or having renal disease were excluded. Retrospective data from five consecutive years of routine blood work results were then analysed for mean serum calcium, albumin, albumin-corrected calcium, vitamin D levels, and the presence of a hypocalcaemic episode (Corrected Ca <8.5 mg/dL).
Results: The mean levels of corrected serum calcium levels were slightly higher among SLE patients than controls (9.23±0.34 vs. 9.19±0.36 mg/dL p≤.001 respectively). In contrast to results of published studies, SLE patients had slightly higher levels of 25(OH)-vitamin D (SLE patients: 22.2±9.06 ng/ml, controls: 20.0±8.76 ng/ml, p≤.001). The most impressive finding entailing SLE patients was that they were twice as likely to experience episodes of hypocalcaemia in comparison to controls (SLE patients: 13.8%, controls: 6.4%, OR 2.34; 95% CI 2.33-2.83).
Conclusions: Calcium levels may play a significant role in the SLE disease process, more than originally thought, since SLE patients are at a higher risk for hypocalcaemic events. Specific changes in vitamin D and calcium homeostasis in SLE patients may be responsible for the severity of symptoms. Further research is required to determine the role of calcium supplementation.