Physiological Responses to Basic Military Training in Conscripts in Conditions of Vitamin D Deficiency and Decreases in Iron Status

Background: High prevalence of vitamin D deficiency has developed in the Estonian population of military conscripts between September and April. Vitamin D status may influence physiological adaptability to training.

Aim: To assess physiological responses to a 10-week basic military training (BMT) in the autumn-winter period in Estonian conscripts.

Methods: Fasting venous blood analysis was performed four times during BMT and once 15 weeks following BMT in 94 conscripts (age and body mass index 20.9 ± 1.7 years and 24.2 ± 3.0 kg ∙ m^–2, respectively).

Results: Significant increases in serum testosterone concentration (60.6%), testosterone to cortisol ratio (61.1%), blood erythrocyte count (4.3%), hemoglobin concentration (3.8%) and hematocrit (2.2%) and decreases in serum ferritin concentration (39.3%) occurred between weeks 1 and 10 during BMT (in all cases p 0.0001). Fifteen weeks later these parameters were still at increased or decreased levels, respectively, compared to week 1. The prevalence of vitamin D deficiency (serum 25(OH)D concentration 50 nmol ∙ L^–1) increased from 42.6% in week 1 to 80.8% in week 10 and to 91.5% 15 weeks later.

Discussion: These findings suggest that BMT induces anabolic physiological adaptations in conscripts despite vitamin D deficiency and decreases in iron status. However, considering the importance of vitamin D for bone health and immune, cardiovascular, lung and muscle function, the adaptations observed may have been limited to a suboptimal level.

Conclusion: Considering that vitamin D influences a variety of functions important for health and performance, vitamin D deficiency in conscripts should be considered a major concern that needs treatment.