Vitamin D status in female military personnel during combat training

Vitamin D is an essential nutrient for maintaining bone health. Sufficient levels of vitamin D, assessed by measuring 25-hydroxyvitamin D (25(OH)D) concentrations, can be defined as the 25(OH)D concentration that either prevents an increase in parathyroid hormone (PTH), a serum calcium regulator suppressed by 25(OH)D, or optimizes calcium absorption [1]. Vitamin D sufficiency may prevent fractures in adults, while insufficiency may result in poor bone mineralization, pain, and rickets in children [2]. According to data collected in the third National Health and Nutrition Examination Survey (NHANES III), women aged 14-30 years in the United States (US) consume less vitamin D from dietary and supplemental sources than other age groups [3]. Suboptimal vitamin D intake and diminished vitamin D status may be particularly important during periods of intense physical activity such as military training, as compromised bone health could contribute to the development of stress fractures. Decrements in nutritional status during US Army basic combat training (BCT) have been documented in female Soldiers [4]. As over 300,000 women serve in the US military, understanding the specific nutritional needs of this population during physical training is critical.Poor vitamin D status has been associated with an increased incidence of stress fracture in Soldiers [5]. Stress fractures are one of the most debilitating injuries in military recruits, and occur most often in military personnel beginning exercise regimens that include unaccustomed and physically-demanding activities. During military training regimens such as BCT, up to 21% of female recruits are diagnosed with at least one stress fracture [6]. The impact of stress fractures on military readiness is notable; the attrition rate of female Soldiers with diagnosed stress fractures may be up to 60% [6,7].Exploring the effects of BCT on vitamin D status in female Soldiers may contribute to the development of improved guidance regard