Vitamin D levels in Portuguese Navy military personnel: a cross-sectional study.

Objectives: Evaluate vitamin D levels in Portuguese active-duty Navy military personnel during winter and explore the relationship between Navy occupational settings and vitamin D levels, as well as between vitamin D levels and fatigue, sleep health, and burnout.

Methods: All active-duty Navy military personnel who collected a blood sample at the Naval Medicine Centre during the winter of 2023-2024 were included in a cross-sectional study. Serum 25-hydroxy-vitamin D (25(OH)D), calcium, phosphorus and parathyroid hormone were added to their analysis request. They were asked to complete a questionnaire that included questions about work, sun exposure, vitamin D-rich foods and/or vitamin D supplements or medication intake, fatigue, sleep health and burnout. Blood samples were processed at the Clinical Pathology Service of the Portuguese Armed Forces Hospital. T-test/median test and z-test were applied to compare homologous means/medians and prevalences, respectively.

Results: Of the 735 participants, 42.2%, 41.1% and 16.7% were vitamin D deficient, insufficient and sufficient, respectively. The median serum 25(OH)D level was significantly lower (p<0.001), and vitamin D deficiency prevalence was significantly higher (p=0.000) in 'onboard' and 'indoors' groups, as well as in the 'mixed shifts' group (p=0.030; p=0.004). Median serum 25(OH)D level was not statistically different between groups with and without fatigue, poor sleep health, and personal or work-related burnout.

Conclusions: The high prevalence of vitamin D deficiency in a sample of Portuguese active-duty Navy military personnel, during winter, especially those working onboard, indoors and with mixed shifts, must be addressed by Navy occupational health services. Future research should include submariners.