A report published in the May, 2008 issue of the Journal of Bone and Mineral Research revealed that supplementing female military recruits with vitamin D and calcium prevented stress fractures, one of the most common overuse injuries that occurs in this population. Stress fractures occur when bones are repetitively loaded over short periods of time without adequate time for repair, and are more common in women than men.
Researchers at Creighton University Osteoporosis Research Center in Omaha, Nebraska, in collaboration with the Naval Institute for Dental and Biomedical Research, Great Lakes, Illinois, randomized 5,201 female Navy recruit volunteers to receive 2000 milligrams calcium and 800 international units vitamin D per day or a placebo, to be consumed with breakfast and dinner over the course of eight weeks of basic training. Three hundred-nine participants were diagnosed with a stress fracture during the treatment period.
Women who received calcium and vitamin D were found to have a 20 percent lower incidence of stress fracture than the placebo group. When the analysis was limited to only those subjects who completed the study, the incidence of stress fracture among the supplemented group was 21 percent lower than the controls. From this data, the researchers predicted that approximately 187 women of the 14,416 who entered basic training at the Great Lakes Naval Station would have been prevented from undergoing a stress fracture by receiving calcium and vitamin D supplements.
To the authors' knowledge, this randomized, controlled trial is the first to demonstrate the efficacy of calcium and vitamin D supplementation on stress fracture prevention. Because the women averaged a low intake of calcium upon enrollment, the researchers remark that their finding was not surprising. The benefits of calcium and on skeletal strength are well established. When calcium intake is insufficient, parathyroid hormone levels increase, which liberates calcium from the skeleton to maintain normal serum calcium levels. Decreased levels of vitamin D can also mildly increase parathyroid hormone levels.
The authors write that the projected decrease in stress fracture that would occur if all basic training recruits received calcium and vitamin D supplements would significantly reduce debilitation and financial costs. "Supplementation with calcium and vitamin D provides a safe, easy, and inexpensive intervention that does not interfere with training goals," they conclude.Related Health Concern: Osteoporosis
Many studies have shown that calcium can reduce bone loss and suppress bone turnover. Calcium intake is a foundation of osteoporosis prevention (Kasper DL et al 2005). Calcium requires the presence of vitamin D for maximum absorption. Although calcium is readily available in dairy products and other dietary sources, many Americans are calcium deficient. There are a few possible explanations for calcium deficiencies:
- Decreased vitamin D availability, possibly due to kidney or liver problems or insufficient exposure to sunshine (ultraviolet radiation)
- Decreased gastrointestinal tract absorption due to stomach or intestinal problems
- Increased loss of calcium from the kidneys
- Increased loss of calcium from the colon and bowels
- Low dietary calcium intake
There are many forms of calcium on the market, including the common calcium carbonate, calcium gluconate, and calcium citrate. Of these, calcium citrate is the most easily absorbed and a good way to receive supplemental calcium. It may also turn out that not only is supplementation vital to preventing and treating osteoporosis but that the timing of the supplementation is important. For example, in a study of healthy volunteers, two doses of 500 mg calcium and 400 IU vitamin D taken six hours apart produced a more prolonged decrease in serum parathyroid hormone levels (low levels of which indicate adequate calcium levels) than a single dose with the same total amounts of calcium and vitamin D.
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