Vitamin D (cholecalciferol) is used in the management of systemic lupus erythematosus (SLE) primarily due to scientific evidence linking vitamin D deficiency with disease activity in lupus patients. Numerous observational studies have shown that individuals with SLE commonly exhibit low serum vitamin D levels, which are associated with increased disease activity, flares, and potentially a greater risk of comorbidities such as cardiovascular disease. The immunomodulatory effects of vitamin D—specifically its role in regulating T-cell and B-cell function, and reducing pro-inflammatory cytokines—provide a biological rationale for supplementation in lupus patients, particularly as photosensitivity in SLE often leads to sun avoidance and thus lower endogenous vitamin D synthesis.

Clinical trials have investigated vitamin D supplementation in SLE patients, with some studies demonstrating modest improvements in disease activity markers (e.g., SLEDAI scores) and reductions in fatigue and proteinuria. However, results are variable, and no large-scale, definitive randomized controlled trials have established a clear benefit for vitamin D supplementation beyond correcting deficiency. Guidelines from rheumatology societies suggest monitoring and correcting vitamin D deficiency in SLE, primarily to support bone health and potentially modulate immune function.

In summary, the use of vitamin D in lupus is scientifically justified, especially for patients with documented deficiency. The overall strength of evidence for direct disease-modifying effects is moderate (rated 3/5), with ongoing research needed to clarify its full therapeutic potential in SLE management.