Introduction: Stress fractures (SFx) are one of the most common and debilitating overuse injuries seen in military recruits, and they are also problematic for non-military athletic populations. The goal of this randomized double-blind, placebo-controlled study was to determine if a calcium and vitamin D intervention could reduce the incidence of SFx in female recruits during basic training.~Methods: We recruited 5201 female Navy recruit volunteers and randomized them to a 2000 mg calcium and 800 IU vitamin D supplement/day or placebo. SFx were ascertained when recruits reported to the Great Lakes clinic with symptoms. All SFx were confirmed with radiography or technetium scan according to the usual Navy protocol.~Results: A total of 309 subjects were diagnosed with a SFx resulting in an incidence of 5.9% per eight weeks. Using intention-to-treat analysis by including all enrolled subjects, Fisher's Exact test found that the calcium and vitamin D group had a 25% lower incidence of SFx than the control group (6.6% vs 5.3%, respectively, p=0.03). The per protocol analysis, including only the 3700 recruits who completed the study, found a 27% lower incidence of fractures in the supplemented vs the control group (8.6% vs 6.8%, respectively, p=0.02).~Conclusions: Generalizing the findings to the population of 14,416 females who entered basic training at the Great Lakes during the 24 months of recruitment, calcium and vitamin D supplementation for the entire cohort would have prevented about 130 persons per year from fracturing. Such a decrease in SFx would be associated with a significant decrease in morbidity and financial costs.
We conducted a double-blind, placebo-controlled randomized clinical trial of calcium and vitamin D supplementation in 5201 female Naval recruits. During 8 weeks of basic training, supplementation with 2000 mg calcium and 800 IU vitamin D/day decreased incidence of stress fracture by 25%. The hypothesis was:~Supplementation with calcium 2000 mg/d and vitamin D 800 IU/d will significantly reduce the incidence of stress fractures in female Navy recruits during 8 weeks of basic training.