Calcium and Vitamin D Supplementation Does Not Affect Iron Status during Initial Military Training: A Randomized, Double-Blind, Placebo-Controlled Trial

Initial military training (IMT) is associated with elevated bone turnover and an increased risk for stress fractures. Supplemental Ca and vitamin D during IMT improves bone health, although previous studies indicate that supplemental Ca intake may interfere with iron absorption, affecting iron status. The objective of this study was to determine the effect of daily Ca and vitamin D supplementation (2000 mg and 1000 IU/day, respectively) on biochemical indicators of iron status during IMT. Biomarkers (hemoglobin, Hgb; serum ferritin, SF; soluble transferrin receptor, sTfR; transferrin saturation TS) were assessed in fasted volunteers (n = 152, males = 98, females = 54; age [mean ± SD] = 21 ± 4 yrs) at the start and end of a 9-wk IMT course. Supplemental Ca and vitamin D were provided in a fortified snack food, which was consumed between meals 2x/day throughout IMT. Iron status declined over the course, as Hgb, SF and TS declined (8, 50, and 37%, respectively; P u003c 0.05; main effect of time) and sTfR increas...