Introduction In Portugal, most adults have inadequate levels of vitamin D. Active duty military personnel need to be always ready for duty, perform tasks in specific contexts and overcome high physical and mental demands, which raises the relevance of knowing their vitamin D levels. This study aims to characterise vitamin D levels of Portuguese active duty military personnel and evaluate the effect of military status on the prevalence of vitamin D sufficiency, adjusted for season of the year, age and gender.

Methods A retrospective cross-sectional study, based on vitamin D measurements carried out at the Armed Forces Hospital between 2014 and 2020, was fulfilled including the variables age, gender, vitamin D level and dosing date for military personnel and civilians. Comparison of proportions test and the generalised linear regression model were used for data analysis with a significance level of 5%.

Results Out of 2782 subjects, 62.7% were military personnel. Mean±SD level of vitamin D was 24.5±10.6 ng/mL and 23.7±11.5 ng/mL in military personnel and civilians, respectively. In the military personnel, the prevalence of vitamin D sufficiency, insufficiency and deficiency was, respectively, 25.2%, 40.1% and 34.6%. Prevalence of vitamin D sufficiency was similar in the civilians cohort and, also, between Armed Forces branches. Military status had no effect on the prevalence of vitamin D sufficiency, especially after adjustments.

Conclusions We present data on vitamin D levels of Portuguese active duty military personnel. Our results found that military personnel are no more at risk of vitamin D inadequacy than civilians, but only a quarter of active duty military personnel had vitamin D sufficiency. Therefore, they can benefit from vitamin D levels assessment towards vitamin D levels optimisation. Further studies are still needed, especially among military personnel with higher risk of vitamin D deficiency.