Page 68 - Journal of Special Operations Medicine - Spring 2014

Figure 2 Ranges for serum 25-hydroxyvitamin D levels in Serum vitamin D levels in the United States have de-
ng/mL. *40–50 ng/mL has been recommended as optimal creased over the past few decades. Sunlight generally
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vitamin D status. Adapted from Endocrine Society Clinical contributes about 90% of vitamin D, with the remain-
Practice Guideline. 5 ing 10% coming from dietary sources. Risk factors for
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vitamin D deficiency include minimal sunlight exposure,
darker skin pigmentation, use of sun block, and wearing
protective clothing.

Outdoor training in tactical gear prevents adequate
skin exposure, as evidenced in female U.S. Army re-
cruits whose vitamin D levels decreased throughout
basic combat training, despite outdoor activities during
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No data have been published on the prevalence of vi- autumn in South Carolina. The pattern of vitamin D
tamin D deficiency in active duty personnel. However, seasonality in the United States shows a peak in August
analysis of archived serum samples from 990 Service- and a nadir in February. For most U.S. latitudes north
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members found that 35% of subjects had serum 25(OH) of Atlanta, GA (33.7°N), UV radiation is inadequate for
D levels less than 20ng/mL. Fifty-seven percent of fe- sufficient endogenous synthesis of vitamin D during the
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male recruits entering basic training had serum 25(OH) winter months. Therefore, individuals training in these
11
D levels less than 30ng/mL, increasing to 75% of recruits regions are dependent on dietary sources of vitamin D.
with low vitamin D after 8 weeks despite outdoor train-
ing. Mean serum 25(OH)D levels in 1200 U.S. Navy Good natural sources of vitamin D are limited to fatty
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3
female recruits were 30ng/mL, while 204 male Finnish fish (salmon, mackerel, tuna) and egg yolks. Addition-
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recruits had mean 25(OH)D levels of 18ng/mL. Male ally, the United States mandates that all dairy milk be
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Lith uanian soldiers had mean 25(OH) levels of 12ng/mL, fortified with 100IU vitamin D per 8 ounces. Manufac-
with 95% of the 262 men deficient in vitamin D. 17 turers may choose to fortify additional dairy products,
nondairy substitutes, or grains. Vitamin D is another
2
These vitamin D levels are similar to those measured in dietary form found in irradiated mushrooms, as well
NHANES data, which estimate that 32% of the U.S. pop- as some fortified foods and supplements. However, the
ulation is deficient in vitamin D. In fact, many experts limited sources of dietary vitamin D may be insufficient
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argue that optimal vitamin D status is serum 25(OH)D to meet vitamin D requirements, especially when sun-
between 40 and 50ng/mL, based on the inability to store light exposure is limited.
vitamin D in muscle and fat tissue at lower levels. Serum
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samples from lifeguards and Tanzania residents show
that individuals with outdoor lifestyles have 25(OH)D Vitamin D Deficiency Inhibits
ranging 45 to 65ng/mL, indicating these levels reflect evo- Physical and Cognitive Performance
lutionary human sun exposure. Based on these reports, Vitamin D receptors and enzymes are present through-
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it is expected that a significant proportion of combat Op- out tissues of the body and contribute to a variety of
erators have insufficient levels of vitamin D, limiting their functions related to bone health, physical performance,
physical and cognitive functioning and potentially com- androgen synthesis, cognitive performance, and neu-
promising their overall performance. roprotection (Figure 3). Vitamin D deficiency leads to

Figure 3 Summary of symptoms related to vitamin D deficiency.

Vitamin D deficiency

Bone Health Physical Performance Androgen Synthesis Cognitive Performance
and Neuroprotection
• Reduced calcium absorption • Reduced muscle strength • Reduced testosterone
• Increased bone turnover • Increased risk for levels • Increased risk for
• Increased risk for stress musculoskeletal injury depression, memory loss,
fracture • Impaired balance and and cognitive decline
neuromuscular function • Increased systemic
inflammation
• Potentially increased risk
for mTBI post-concussive
symptoms and PTSD

60 Journal of Special Operations Medicine Volume 14, Edition 1/Spring 2014