Abstract
Primary antiphospholipid syndrome (PAPS) is a systemic autoimmune disorder, characterised by consistently high levels of antiphospholipid antibodies, thrombosis, and/or pregnancy morbidity. Due to various suspected causes, deficient or insufficient levels of vitamin D in the serum have been reported in patients with PAPS; however, the reports have been sporadic and inconclusive. This systematic review and meta-analysis aimed to comprehensively evaluate the serum vitamin D levels in patients with PAPS compared to controls. A protocol was registered in PROSPERO (Registration No. CRD42019132128) and a systematic literature search was conducted through Google Scholar, PubMed, Web of Science, Scopus, and ScienceDirect databases without restricting language and year. Pooled prevalence, mean difference (MD), and odds ratio (OR) along with 95% confidence intervals (CI) were determined by using a random effects model. Study quality was assessed by the Joana Brigg's Institute (JBI) protocol and publication bias was evaluated by a trim and fill funnel plot, Begg's, and Egger's tests. The pooled prevalence of vitamin D deficiency and insufficiency was found to be 32.2% [95% CI: 16.3-48.2] and 61.5% [95% CI: 40.2-82.8], respectively. Serum levels of vitamin D were considerably lower in the PAPS patients compared to controls (MD: -5.75, 95% CI: -9.73 to -1.77; p = 0.005). Multiple sensitivity analyses showed that the results remained statistically significant, demonstrating the robustness of this meta-analysis. No significant publication bias was detected in determining the MD of serum vitamin D levels in PAPS and controls. In conclusion, PAPS patients had greater rates of vitamin D deficiency or insufficiency, higher frequency of thrombosis, and lower serum vitamin D levels than healthy individuals.