Background: Systemic lupus erythematosus (SLE) is a systemic autoimmune disease where chronic inflammation and tissue or organ damage is observed. Due to various suspected causes, inadequate levels of vitamin D (a steroid hormone with immunomodulatory effects) has been reported in patients with SLE, however, contradictory.
Aims: The aim of this systematic review and meta-analysis was to evaluate the serum levels of vitamin D in patients with SLE in compared to healthy controls.
Methods: PubMed, SCOPUS, ScienceDirect and Google Scholar electronic databases were searched systematically without restricting the languages and year (up to March 2, 2019) and studies were selected based on the inclusion criteria. Mean difference (MD) along with 95% confidence intervals (CI) were used and the analyses were carried out by using a random-effects model. Different subgroup and sensitivity analyses were conducted. Study quality was assessed by the modified Newcastle-Ottawa Scale (NOS) and publication bias was evaluated by a contour-enhanced funnel plot, Begg's and Egger's tests.
Results: We included 34 case-control studies (2265 SLE patients and 1846 healthy controls) based on the inclusion criteria. Serum levels of vitamin D was detected significantly lower in the SLE patients than that in the healthy controls (MD: -10.44, 95% CI: -13.85 to -7.03; p < .00001). SLE patients from Asia (MD: -13.75, 95% CI: -21.45 to -6.05; p = .0005), South America (MD: -3.16, 95% CI: -4.62 to -1.70; p < .0001) and Africa (MD: -16.15, 95% CI: -23.73 to -8.56; p < .0001); patients residing below 37° latitude (MD: -11.75, 95% CI: -15.79 to -7.70; p < .00001); serum vitamin D during summer season (MD: -7.89, 95% CI: -11.70 to -4.09; p < .0001), patients without vitamin D supplementation (MD: -15.57, 95% CI: -19.99 to -11.14; p < .00001) or on medications like hydroxychloroquine, corticosteroids or immunosuppressants without vitamin D supplementation (MD: -16.46, 95% CI: -23.86 to -9.05; p < .0001) are in higher risk in presenting inadequate serum levels of vitamin D. The results remained statistically significant from different sensitivity analyses which represented the robustness of this meta-analysis. According to the NOS, 91.2% of the studies were considered as of high methodological quality (low risk of bias). No significant publication bias was detected from contour-enhanced and trim and fill funnel plots or Begg's test.
Conclusion: Inadequate levels of serum vitamin D is significantly high in patients with SLE compared to healthy subjects, therefore, vitamin D supplementation with regular monitoring should be considered as part of their health management plans.
Keywords: 25(OH)D; Meta-analysis; Systematic review; Systemic lupus erythematosus (SLE); Vitamin D.
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