The Sunshine Paradox: A Systematic Review and Meta-Analysis of Vitamin D Deficiency Burden and Modifiable Risk Factors in Libya

Background: Libya receives abundant ultraviolet B (UVB) radiation year-round (>3,000 hours of sunshine annually), theoretically sufficient for adequate endogenous vitamin D synthesis. Paradoxically, emerging epidemiological reports suggest a high burden of vitamin D deficiency (VDD) across diverse Libyan populations—a phenomenon termed the "Sunshine Paradox." This contradiction may reflect the influence of modifiable behavioral, cultural, and environmental factors (e.g., limited intentional sun exposure, full-coverage clothing, urbanization, dietary insufficiency, low supplementation uptake) that override geographic advantage. However, existing studies are fragmented, methodologically heterogeneous, and lack quantitative synthesis. Purpose: This systematic review and meta-analysis aims to: (1) estimate the pooled national prevalence of vitamin D deficiency (serum 25-hydroxyvitamin D [25(OH)D] <20 ng/mL [<50 nmol/L] and/or <30 ng/mL [<75 nmol/L]) among Libyan residents of any age, sex, or health status; (2) identify and quantify associations between VDD and modifiable risk factors, including sun exposure practices, clothing coverage, dietary intake, supplementation use, body mass index, and place of residence; (3) explore sources of heterogeneity across studies through subgroup analyses and meta-regression (e.g., by sex, age group, geographic region [coastal vs. inland], assay methodology, publication year); and (4) generate evidence-based, context-appropriate recommendations for public health policy, clinical screening, and future research. Methods Overview: Following PRISMA 2020 guidelines and prospective registration on OSF, we will search PubMed/MEDLINE, Scopus, Web of Science, Embase, African Index Medicus, IMEMR, and regional Libyan databases from inception to [Insert end date]. Observational studies (cross-sectional, cohort baseline, case-control) reporting serum 25(OH)D-based VDD prevalence or risk factor associations in Libyan populations will be included. Two independent reviewers will conduct screening, data extraction, and quality appraisal using the Joanna Briggs Institute (JBI) checklist. Pooled prevalence will be estimated using random-effects meta-analysis with logit transformation and restricted maximum likelihood (REML) estimation. Hartung-Knapp adjustments, subgroup analyses, and meta-regression will address heterogeneity. Publication bias will be assessed via funnel plots and Egger's test. Expected Outcomes & Significance: This review will provide the first nationally representative, methodologically rigorous synthesis of VDD burden in Libya. We anticipate confirming a high prevalence of deficiency despite ample solar irradiance, with behavioral and cultural factors emerging as dominant drivers. Findings will directly inform: (1) targeted screening strategies for high-risk groups (e.g., women, adolescents, urban dwellers); (2) culturally adapted public health interventions (e.g., sun-exposure guidelines, food fortification advocacy, supplementation protocols); and (3) standardized surveillance frameworks for vitamin D status in Libya and comparable sun-rich, resource-limited settings. By clarifying the modifiable determinants of the Sunshine Paradox, this work supports actionable pathways to reduce the preventable burden of vitamin D deficiency in Libya. Keywords: vitamin D deficiency; Libya; Sunshine Paradox; systematic review; meta-analysis; prevalence; risk factors; public health nutrition; MENA region; 25-hydroxyvitamin D.