Female arm recruits receiving the daily supplements experienced 20 per cent fewer stress fractures than their un-supplemented counterparts, according to research published in the Journal of Bone and Mineral Research .
The results were obtained from a randomized, double-blind study with 5,201 female U.S. Navy recruits during eight weeks of basic training.
"Generalizing the findings to the population of 14,416 women who entered basic training at the Great Lakes during the 24 mo of recruitment, calcium and vitamin D supplementation for the entire cohort would have prevented 187 persons from fracturing," wrote the authors from Creighton University Osteoporosis Research Center in Nebraska and the Naval Institute for Dental and Biomedical Research.
Stress factures are said to be one of the most common and debilitating overuse injuries seen in U.S. military recruits with 21 per cent of female recruits reported to suffer from this form of injury.
Male recruits suffer less.
Such fractures are also problematic for athletic people outside of the military.
"Such a decrease in stress fracture would be associated with a significant decrease in morbidity and financial costs," they added.
The combination of vitamin D and calcium has long been recommended to reduce the risk of bone fracture for older people, particularly those at risk of or suffering from osteoporosis, which is estimated to affect about 75m people in Europe, USA and Japan.
The action of the nutrients is complimentary, with calcium supporting bone formation and repair, while vitamin D helps the body absorb calcium.
Study details The researchers randomly assigned the recruits to receive daily supplements of 2,000 mg of calcium and 800 IU of vitamin D, and the other group received a placebo.
At the end of the eight weeks of basic training, 309 women developed stress fractures.
Women receiving the vitamin-mineral combination were 20 per cent less likely to experience the fractures, report the researchers.
Moreover, when the results were concerned with only the 3700 recruits who completed the study, the reductions in the incidence of fracture was of a similar magnitude - 21 per cent fewer fractures than the placebo group.
Further studies are needed to confirm these findings, but the results appear to fit with numerous other studies linking the nutrients to improved bone health.
The current EU recommended daily intake of calcium is 800mg, with an upper safe limit of 2500mg.
Vitamin D has a RDI of 400 IU, although campaigners are calling for an increase to 1000 IU, half the upper safe limit recommended by the EU and US.
In the US, the DRI (dietary reference intake) for calcium is 1000mg for adults aged 19 to 50, and 1200mg from 51 to 70.
For vitamin D it is five micrograms per day, rising to 10 after the age of 50.
The study was funded by the U.S. Department of Defense.
Source: Journal of Bone and Mineral Research May 2008, Volume 23, Pages 741-749, doi: 10.1359/jbmr.080102 "Calcium and Vitamin D Supplementation Decreases Incidence of Stress Fractures in Female Navy Recruits" Authors: Joan Lappe, D. Cullen, G. Haynatzki, R. Recker, R. Ahlf, K. Thompson