Vitamin D protects teenage girls from stress fractures
MedWire News: Girls who consume a high level of vitamin D have a reduced chance of stress fractures when participating in high-impact sports, shows research that found no such protection with a high intake of calcium or dairy products.
"Stress fracture is a frequent cause of injury in recreational athletes, with consequences ranging from delayed return to full sport participation and reoccurrence of injury," explain Kendrin Sonneville (Children's Hospital Boston, Massachusetts, USA) and co-authors in the Archives of Pediatric and Adolescent Medicine.
"Given the limited knowledge of modifiable risk factors for stress fracture among adolescent girls, the results of this study provide important information regarding the role of dietary factors in the prevention of stress fracture."
The researchers collated information on dairy, calcium and vitamin D intake for 6712 US girls aged 9-15 years who participated in the Growing Up Today Study. The girls' mothers completed a food frequency questionnaire every 12-24 months between 1996 and 2001.
The majority of the girls had a healthy weight, with 8.6% underweight, and 19.8% overweight or obese. A third (30.4%) took part in high-impact activities for at least 1 hour per day.
The girls consumed an average of 2.0 servings of dairy each day, and average intakes of calcium and vitamin D were 1181.5 mg/day and 376.2 IU/day, respectively.
Of note, at baseline the girls' intakes of calcium and vitamin D were significantly below the recommended dietary allowances of 1300 mg/day and 600 IU/day for their age group.
The participants were followed up for 7 years, during which time 3.9% sustained a stress fracture.
Sonneville et al found that the risk for stress fracture did not significantly differ between girls consuming no dairy and those consuming three or more portions per day. Nor was there a significant correlation between stress fractures and consumption of dietary or supplemental calcium intake.
After adjusting for confounding factors, such as age, body mass index, age at menarche, and maternal history of low bone density, the researchers found a significant correlation between vitamin D and fracture risk.
Girls in the highest quintile for vitamin D intake (663 IU/day) were half as likely to develop stress fractures as those in the lowest quintile (107 IU/day; hazard ratio [HR]=0.49).
These findings were confirmed in data for girls participating in high-impact activities, with a HR of 0.48 for highest versus lowest quintile of vitamin D. Dairy intake had no impact on stress fracture risk in this population and although high intake of calcium was associated with a trend towards an increased risk for stress fracture, this was not statistically significant.
Sonneville et al conclude: "Future studies are needed to ascertain whether vitamin D intake from supplements confers a similarly protective effect as vitamin D consumed through dietary intake."
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By Lynda Williams