Background: Chronic Fatigue Syndrome (CFS) is a debilitating condition considered by persistent, unexplained fatigue that significantly impairs daily functioning. Emerging evidence suggests a potential link among CFS and serum vitamin D deficiency, although the extent of this association remains unclear. Our current systematic review and meta-analysis aim to comprehensively assess incidence and severity of serum vitamin D absence in CFS patients. Methods: A complete search was led in major electronic databases to identify related studies published up to September 2021. Studies reporting serum vitamin D levels in CFS patients were included. Data extraction, quality assessment, and statistical analysis were performed using established methodologies. Random-effects meta-analysis models were used to estimate pooled occurrence rates and mean serum vitamin D levels, with subgroup analyses led to discover potential sources of heterogeneity. Results: Our search identified overall 15 researches that met our inclusion criteria. The combined data from these studies revealed a significantly higher occurrence of serum vitamin D shortage in CFS individuals associated to healthy controls. The meta-analysis showed that CFS individuals had, on average, lower serum vitamin D levels associated to healthy individuals (pooled mean variance: -5.12 ng/mL, 95% CI: -7.45 to -2.79). Moreover, prevalence of vitamin D deficiency (defined as serum 25-hydroxyvitamin D <20 ng/mL) remained significantly higher in CFS individuals (pooled prevalence: 54.7%, 95% CI: 43.1% to 66.2%) compared to healthy controls (pooled prevalence: 31.3%, 95% CI: 22.1% to 40.6%). Conclusion: Our current systematic research and meta-analysis provide robust evidence of a high occurrence of serum vitamin D shortage in CFS individuals, having severity levels warranting clinical attention. These findings highlight the importance of routine screening for vitamin D shortage in CFS patients and suggest very possible avenue for further research into the mechanisms underlying this association.
Keywords: Chronic Fatigue Syndrome, CFS, Serum Vitamin D, Deficiency, Prevalence, Severity, Systematic Review, Meta-Analysis.