Increasing Prevalence of Potential Vitamin D Toxicity and Its Risk Factors in Korea: A Large Population-Based Study

<b>Background/Objectives</b>: Vitamin D plays an important role in a wide range of health outcomes, including immune regulation, bone metabolism, cardiovascular health, and cancer prevention. However, recent data on the prevalence and risk factors for elevated serum 25-hydroxyvitamin D [25(OH)D] concentrations-indicative of potential vitamin D toxicity-remain limited in Korea. <b>Methods</b>: We conducted a retrospective analysis of laboratory data from individuals who underwent serum 25(OH)D testing between 2020 and 2022. Potential vitamin D toxicity was defined as serum 25(OH)D levels exceeding 50, 100, or 150 ng/mL. The prevalence of potential toxicity was examined by age, sex, test month, and year. <b>Results</b>: A total of 1,198,947 individuals (mean age, 45.7 ± 19.4 years; 31.6% male) were included in the study. The prevalence of serum 25(OH)D > 50 ng/mL increased from 4.41% in 2020 to 6.21% in 2022, and that of >100 ng/mL rose from 0.09 to 0.12% over the same period. The proportions exceeding 50 and 100 ng/mL also rose significantly (<i>p</i> < 0.05), while >150 ng/mL remained rare (0.01%) and stable. Elevated 25(OH)D concentrations were more frequently observed among females, children aged 0-9 years, and adults aged ≥50 years (adjusted odds ratios for multivariable logistic regression > 1.0, <i>p</i> < 0.05). <b>Conclusions</b>: Although the prevalence of potential vitamin D toxicity remains low, its continuous upward trend highlights the need for increased public awareness, clinical monitoring, and guideline-based supplementation strategies to prevent inadvertent vitamin D intoxication, particularly in the aging population.