Nutrient effects on stress reaction to bone.

Pain complaints related to periostitis and stress fractures are common in active individuals. This spectrum of “stress reaction” to bone is usually associated with untrained athletes who are making a lifestyle choice and beginning activity, or conditioned athletes who increase the intensity, frequency, or duration of training. The role of calcium and vitamin D in bone health is undisputed. Since 1997, the Canadian and American governments have recommended a daily allowance for vitamin D for adults of 600 IU per day. Many experts believe this value is inadequate and continue to advocate for a higher recommended daily allowance for vitamin D.1 In 2007 the Canadian Cancer Society recommended a daily intake of 1000 IU of vitamin D, advocating for the beneficial effects of vitamin D in the prevention of colorectal, breast, and prostate cancer.2 Vitamin D is synthesized in the skin; UVB solar exposure converts 7-dehydrocholesterol to vitamin D. In Canada there is a seasonal variation to vitamin D synthesis, with levels at their lowest in the winter months.3-7 About 20 000 IU of vitamin D are produced from a single 15-minute, midday, whole-body exposure to sunlight.8 However, this is negatively affected by clothing and sunscreen. In winter months, at latitudes beyond 42°N the solar angle is too oblique for vitamin D synthesis,3 contributing to increased deficiency between October and April. Foodsource supplementation has become the main source of vitamin D where solar exposure is limited. Food products provide about 200 IU of vitamin D per day.9 Health Canada recommends that, in addition to following Canada’s Food Guide, those older than 50 years of age should take a daily vitamin D supplement of 400 IU daily. Vitamin D is required at all phases of skeletal development and is essential for the mediated transport of calcium to produce mineralized bone matrix. Bone resorption markers are detected with vitamin D levels less than 60 nmol/L, and parathyroid hormone (PTH) increases with vitamin D levels less than 78 nmol/L. Inadequate vitamin D results in secondary hyperparathyroidism, increased bone turnover, accelerated bone loss, and increased fracture risk. Previous research has variably demonstrated both positive and negative relationships between calcium and vitamin D levels and stress fractures. Previous research identified that athletes with stress fractures had lower calcium intake.10 Calcium supplementation has a positive linear relationship to spinal trabecular bone density in amenorrheic elite athletes.11 But calcium intake did not correlate with stress fractures and bone mineral density in female army recruits,12 and calcium in the diet did not alter stress fractures in elite cross-country athletes.13 Vitamin D levels have been shown to be lower in Israeli military personnel with stress fractures,14 but calcium and vitamin D levels have not been related to stress fractures in adolescent girls.15 In 179 Finnish military recruits, stress fractures were associated with high PTH levels but not low vitamin D levels. Because Finnish men have poor vitamin D status, vitamin D supplementation to lower PTH and reduce the incidence of stress fractures was recommended.16 In another study, serum vitamin D was significantly lower among 756 Finnish military recruits in those with stress fractures (odds ratio = 3.6, 95% CI 1.2 to 11.1).17 More recent studies have identified a 20% decrease in stress fractures in American military recruits using calcium and vitamin D supplementation.18 The balance of current research provides evidence to suggest that maintaining adequate vitamin D status might reduce stress fracture risk in athletic populations.19 EDITOR’S KEY POINTS • Pain related to periostitis and stress fractures is common among active individuals, particularly untrained athletes becoming active and conditioned athletes increasing the intensity, frequency, or duration of training. Supplementation with calcium and vitamin D aids in optimizing bone health and might reduce the incidence of stress reaction to bones in active individuals.