Prevalence of Vitamin D Hypovitaminosis in Croatia: A Cross-Sectional Study Based on Routine Clinical Examinations.

Background/Objectives: Vitamin D deficiency is recognized as a global public health concern due to its implications for bone health, immune regulation, and chronic disease risk. Despite its significance, comprehensive data on the prevalence of hypovitaminosis D in the Croatian population remain limited. This study aimed to determine the distribution of 25-hydroxyvitamin D (25-OH D) levels in a group of patients who underwent routine clinical examination, evaluate the prevalence of deficiency, and assess potential associations with demographic factors such as age and sex. Methods: This cross-sectional study included 829 individuals aged 19-85 years who underwent routine clinical testing at our institution. Serum 25-OH D concentrations were measured and classified as normal (≥75 nmol/L), deficient (<75 nmol/L, ≥50 nmol/L), or severely deficient (<50 nmol/L). Data on age and sex were extracted, and statistical analyses included descriptive statistics, tests for normality (Kolmogorov-Smirnov), comparisons (Mann-Whitney U, Kruskal-Wallis), and correlation testing (Spearman's rho). Significance was set at p < 0.05. Results: The cohort consisted of 525 females (63.3%) and 304 males (36.7%), with a mean age of 49.2 ± 15.8 years. The mean and median serum 25-OH D concentrations were 53.5 and 53.0 nmol/L, respectively (IQR: 40.0-65.0). Severe deficiency (<50 nmol/L) was present in 43.7% of participants, while an additional 49.2% exhibited moderate deficiency, leaving only 7.1% with sufficient levels. No statistically significant differences in vitamin D levels were observed between sexes, nor was there a significant correlation between age and vitamin D concentration (p > 0.05). Conclusions: Vitamin D deficiency is highly prevalent in the Croatian population, with more than 90% of individuals showing suboptimal serum levels. The absence of significant associations with age or sex suggests a widespread deficiency pattern, underscoring the need for nationwide preventive strategies, including dietary supplementation and public health education initiatives to improve vitamin D status.