Lappe et al. 2008, calcium and vitamin D RCT in female Navy recruits

Randomised, double-blind, placebo-controlled trial in 5,201 female Navy recruits. Daily 2,000 mg calcium plus 800 IU vitamin D during basic training cut stress-fracture incidence by about 20% versus placebo. Strong as a large RCT, though in a recruit population under heavy new loading rather than trained runners.