Retrospective, observational, and anonymous study to assess vitamin D status in young medical residents of both sexes who joined the staff of the Reina Sofia University Hospital (HURS) in Cordoba, Spain, in March 2020. Subjects with vitamin D deficiency were treated with calcifediol and reevaluated. The retrospective cohort study was approved (October 29, 2025) by the Provincial Committee on Ethics in Drug Research (CEIm) of Córdoba (Spain), [committee reference number 6337) Communication/application code: SICEIA-2025-002858]. Data Based on the files of the HURS occupational medicine service.

Vitamin D deficiency, expressed as circulating levels of 25-hydroxyvitamin D (25OHD), the sum of 25OHD2 and 25OHD3, is highly prevalent worldwide. Regardless of geographical location and climate, 88% of the world's population has serum 25OHD concentrations below 30 ng/ml; 37% have values below 20 ng/ml and up to 7% have levels below 10 ng/ml. In all regions of Spain, there is a prevalence of vitamin D deficiency similar to that in the rest of the world, which is also high in patients undergoing treatment for osteoporosis. All studies of different population and age subgroups, such as those grouped in the Asturias and Pizarra (Málaga) cohorts, as reported in a recent review , support this fact. It should be noted that the prevalence of 25OHD deficiency is high in winter, even in southern provinces of Spain .

High levels of hypovitaminosis D have been reported in young, healthy adults, medical residents beginning their specialisation training at the Doce de Octubre Hospital in Madrid (Spain), where the majority, aged between 21 and 41, suffered from vitamin D deficiency or insufficiency. Studies with similar characteristics reveal similar data worldwide. A review by McKenna of 117 studies published between 1971 and 1990 on vitamin D concentrations in 27 different regions of the world, 42 of them in young adults, revealed that more than 40% of young adults in Western and Central Europe suffered from vitamin D deficiency during the winter. A study conducted in Boston with healthcare workers aged 18-49 revealed serum concentrations of 25OHD < 20ng/ml in 36% of subjects aged 18-29 at the end of winter (March and April). Another study conducted on internal medicine residents at a hospital in Portland, Oregon, with an average age of 30.1 years for women and 30.6 years for men, revealed 25OHD levels < 20ng/ml in 47% of resident doctors during the months of March and April, and 74% of participants had lower serum 25OHD concentrations in spring than in autumn.

Resident doctors who joined HURS in the spring of 2020 may be vulnerable to low 25OHD levels due to long hours of study preparing for competitive examinations, compounded by lockdown and the subsequent lack of exposure to sunlight The hospital's Occupational Medicine Service assessed vitamin D (25OHD) levels to identify vitamin D deficiency. This deficiency can have functional repercussions in addition to its effects on musculoskeletal metabolism and the innate and adaptive immune systems, among other important functional repercussions. Treatment with calcifediol was initiated in those with deficiencies with the aim of normalising serum 25OHD levels.

Calcifediol offers pharmacokinetic advantages that give it a certain functional superiority over native vitamin D3. It is highly hydrophilic and, therefore, after oral ingestion, it is absorbed through the portal venous system and does not require hydroxylation at position 25, which immediately increases the optimal circulating concentrations of 25(OH)D3. Therefore, when administered orally, it is available in high concentrations within a few hours, and in a stable form, to be a substrate for the synthesis of calcitriol in the kidney and other target organs.

This is not a patient registry. This study is a retrospective observational cohort analysis based on existing occupational health records. No prospective data collection or registry infrastructure was established

Inclusion Criteria:

• Physicians admitted to the Residency Programme at Reina Sofía University Hospital

Exclusion Criteria:

• Subjects for whom there is no data collected in the occupational medicine medical recordrds

Medical residents admitted to the Reina Sofia University Hospital Residency Program

The information collected will be of public access by request