San Diego Sunshine Improves But Does Not Correct Low Vitamin D Levels In Military Recruits

Musculoskeletal injuries (MSKI) impair military readiness and are partially attributed to low vitamin D. MSKI risk is higher in females during military training, but sex related differences in vitamin D levels are unclear. Changes in vitamin D from sun exposure over 10 weeks of training are unknown. PURPOSE: This study assessed vitamin D levels and MSKI in military recruits across 10 weeks of training. METHODS: Marine Corps recruits volunteered for the study during the Spring (SPRG) and Summer (SUM) (females: n = 58, 19.1 ± 2.0 yrs, 161.4 ± 6.9 cm, 61.0 ± 8.4 kg, 26.0 ± 6.1 % body fat; males: n = 42, 18.5 ± 1.1 years, 175.0 ± 6.9 cm, 71.7 ± 6.9 kg, 12.6 ± 4.9 % body fat). Dried blood spot samples were collected at weeks 1 (PRE) and 10 (POST) to assess 25-hydroxyvitamin D (25(OH)D) concentration. Sufficient vitamin D status was ≥30 ng/ml. Injury data were provided by the sports medicine department. RESULTS: Concentrations of 25(OH)D increased from PRE to POST in females (16.5 ± 5.5 ng/ml vs. 24.3 ± 4.0 ng/ml, p < 0.001) and males (21.4 ± 7.5 ng/ml vs. 27.5 ± 5.1 ng/ml, p < 0.05) during SPRG. During SUM, 25(OH)D increased from PRE to POST in females (22.2 ± 5.4 ng/ml vs. 29.7 ± 5.6 ng/ml, p < 0.001) and males (26.0 ± 6.8 ng/ml vs. 31.7 ± 7.3 ng/ml, p < 0.005). Females had significantly lower 25(OH)D concentrations than males at PRE in SPR and SUM (p < 0.001). No females at PRE had sufficient 25(OH)D concentrations in SPRG, while 3% were sufficient in SUM. Sufficient 25(OH)D concentrations were found in 11% and 33% of males in SPRG and SUM, respectively, at PRE. Female (4%) and male (33%) recruits had sufficient 25(OH)D concentrations at POST in SPRG, while SUM recruits had 44% (female) and 56% (male). Twenty-six females (45%) and 7 males sustained an MSKI. Stress fractures represented 15% of female injuries, all of whom had insufficient (20-30 ng/mL) or deficient 25(OH)D concentrations (<20 ng/ml) at PRE. Of male MSKI, 70% had insufficient or deficient 25(OH)D levels at PRE. CONCLUSION: Nearly all recruits entered training with insufficient vitamin D. Despite an 18-32% increase, this improvement was inadequate to achieve sufficient 25(OH)D levels. Females had lower 25(OH)D than males and sustained greater injuries including stress fractures. Sufficient vitamin D is crucial for immune and bone health, and deficiency is easily treatable. Supported by: This work was supported by the Defense Health Agency under work unit no. N1627