Vitamin D deficiency among adults screened for orthodontic treatment in Saudi Arabia: prevalence and implications for trial recruitment

Vitamin D deficiency remains highly prevalent in the Middle East and may influence both oral-health research planning and orthodontic trial feasibility. This study estimated vitamin D deficiency prevalence in adults screened for orthodontic treatment in Saudi Arabia and quantified the resulting biochemical screening burden for a prospectively registered parent randomized controlled trial. Of 525 consecutively approached adults, 400 aged 18–40 years completed baseline assessment for comprehensive fixed-appliance orthodontic treatment at a tertiary center in Madinah, Saudi Arabia, between January and March 2026 and constituted the analytic screening cohort. Serum 25-hydroxyvitamin D [25(OH)D] was quantified by LC-MS/MS in a centralized hospital laboratory. Fresh samples were processed on the day of collection and analyzed in daily analytical runs, with assay precision monitored using daily internal quality controls. The primary deficiency cutoff was serum 25(OH)D < 50 nmol/L. Exact binomial confidence intervals were calculated, and exploratory associations with deficiency were examined using modified Poisson regression with robust standard errors. Vitamin D deficiency was identified in 280 of 400 participants (70.0%; 95% CI, 65.2–74.5). Fifty-six participants (14.0%; 95% CI, 10.8–17.8) had serum 25(OH)D concentrations from 50 to < 75 nmol/L, and 64 (16.0%; 95% CI, 12.5–20.0) had concentrations ≥ 75 nmol/L. Overall, 120 participants (30.0%; 95% CI, 25.5–34.8) had concentrations ≥ 50 nmol/L, whereas 336 (84.0%; 95% CI, 80.0-87.5) had concentrations < 75 nmol/L. These threshold-specific distributions illustrate how biochemical classification can influence screening yield. Deficiency was more common in females than males (74.6% vs. 63.7%; P = 0.026). In the exploratory multivariable model, male sex and daily dietary vitamin D intake were associated with lower deficiency prevalence. Vitamin D deficiency was highly prevalent in this adult orthodontic screening cohort. The proportion above different serum 25(OH)D boundaries varied substantially, with implications for biochemical screening workload and recruitment planning in high-prevalence settings. The present study did not evaluate orthodontic treatment outcomes. ClinicalTrials.gov, NCT07286474. Registered on 16 December 2025, before recruitment and any studyspecific screening procedures. This crosssectional report uses prospectively collected baseline screening data obtained during recruitment for the registered parent trial and does not report randomized allocation, interventions, or treatment outcomes.