Systemic lupus erythematosus (SLE) is a chronic disease characterized by inflammatory response and abnormal autoimmune disease. Vitamin D is essential in phosphorus-calcium metabolism and it has immunosuppressive properties, being considered as a therapeutic option. There is controversy about the role of this vitamin in the pathogenesis of SLE. Thus, the aim of this study was to investigate the influence of the dietary intake of vitamin D and supplementation of vitamin D in a cohort of patients with SLE. A cross-sectional study including a total 285 patients with SLE was conducted (248 females y 26 males; mean age 46.99 ± 12.89 years). The SLE Disease Activity Index (SLEDAI-2K) and the SDI Damage Index were used to asses disease activity and disease-related damage, respectively. Levels of C-reactive protein (CRP; mg/dL), homocysteine (Hcy;mol/L), anti-double stranded DNA antibodies (anti-dsDNA) (IU/mL), complement C3 (mg/dL), and complement C4 (mg/dL), among other biochemical markers, were measured. The dietary intake of vitamin D and the intake of vitamin D supplement were obtained via a 24-h patient diary. 57.1% of the patients were taking vitamin D supplements and the average of dietary vitamin D was 2.08 ± 2.94 μg / day. Note that 98.2% of patients did not reach the recommended dietary intakes for vitamin D intake. Multivariate regression analysis revealed that clinical and laboratory variables are not significantly affected by vitamin D intake levels after adjusting for age, gender, energy intake, and medical treatment (immunosuppressants, corticosteroids and antimalarials). Patients with SLE who took vitamin D supplements had significantly higher serum levels complement C3 compared to patients who did not take them after adjusting for covariates (13.66 ± 9.50 vs. 11.05 ± 3.18; p = 0.016 respectively). Our findings suggest a potential impact of supplementation of vitamin D on the activity of SLE. Future longitudinal research on SLE patients, including intervention trials, are required to validate these preliminary data.