Prevalence and correlates of vitamin D deficiency in a mixed-age hospital-based cohort

Vitamin D deficiency is a pervasive global health issue with significant implications for skeletal and extra-skeletal health. While its prevalence is well-documented in temperate climates, data from large, mixed-age hospital-based cohorts in subtropical regions of China remain limited. This study aimed to determine the precise prevalence and key correlates of vitamin D status in a large and diverse patient population to identify the most vulnerable subgroups.

A retrospective, cross-sectional analysis was conducted on 22,484 valid serum 25-hydroxyvitamin D [25(OH)D] test results from patients at Liuyang Maternal and Child Health Care Hospital (March 2024-September 2025). Vitamin D status was categorized as deficient (≤ 20 ng/mL), low (21-29 ng/mL), or optimal (≥ 30 ng/mL). Group differences were assessed using chi-square tests, and correlations were evaluated with Spearman's rank coefficient.

The overall prevalence of vitamin D deficiency was 10.3% (2,314/22,484), with 27.7% (6,221/22,484) low and 62.0% (13,949/22,484) optimal. The mean 25(OH)D concentration was 33.8 ± 11.9 ng/mL. A strong inverse correlation was observed between 25(OH)D and age (ρ = -0.351, p < 0.001). Deficiency rates varied markedly by age, being lowest in infants/neonates (3.1%) and young children (4.2%), but highest in adolescents (18.2%) and adults aged 18-39 (17.2-17.3%). Females had a significantly higher deficiency rate than males (13.1% vs. 5.8%, p < 0.001). A pronounced seasonal variation was evident, with deficiency peaking in spring (19.5%) and reaching its nadir in fall (4.5%). A weak inverse correlation was found between 25(OH)D and vitamin A (ρ = -0.036, p = 0.011).

This large-scale hospital-based analysis reveals a significant burden of vitamin D deficiency, with a highly heterogeneous distribution across demographic and seasonal strata. The disproportionately high risk identified among adolescents, younger adults (particularly women), and during spring months underscores the critical need for targeted screening and intervention strategies for these specific vulnerable subgroups within similar clinical settings in subtropical China.