The primary objective of this randomized, double-blind, placebo-controlled trial is to determine the effect of vitamin D and calcium supplementation (800IU and 2000mg, respectively) on biochemical indicators of nutritional status and bone health in military personnel during Army basic combat training (BCT) and Air Force basic military training (BMT).

The investigators hypothesize that daily supplementation with vitamin D and calcium during military training will improve vitamin D status, stabilize PTH levels, and result in improvements in markers of bone health. As a result of the investigators study design, the findings will provide critically important data regarding the concentration of vitamin D in blood necessary to stabilize PTH levels and to optimize bone formation during initial military training.

Vitamin D is an essential nutrient for maintaining bone health. Previous work from our laboratory indicates that vitamin D status may decline in Soldiers during BCT, even during the summer months in the Southeastern United States. Stress fractures may affect up to 5% of male and 21% of female Soldiers during training, resulting in attrition in up to 60% of affected personnel, but a recent report indicates that vitamin D and calcium supplementation may attenuate stress fracture risk by up to 20% in female Navy recruits. However, biochemical measures of nutritional status and associated markers of bone health were not collected in that study, leaving questions regarding the vitamin D and calcium requirements for military personnel during periods of elevated bone turnover.

Inclusion Criteria:

• Female or male US Army or US Air Force Recruits
• Participating in Basic Combat Training or Basic Military Training, respectively

Exclusion Criteria:

• Pregnant or breastfeeding
• History of kidney stones or kidney disease