By Shari Roan, Los Angeles Times

Vitamin D may be helpful in protecting highly active pre-teen and teen girls, such as those who play sports, from stress fractures, researchers reported this month.

The study was surprising because calcium has long been considered the nutrient most vital to bone health in children. But, in developing children, vitamin D intake may matter more.

Researchers analyzed data from 6,721 girls ages 9 to 15 at the start of the study. The girls’ intake of calcium, vitamin D and dairy products was recorded along with stress fractures, which are common sports-related injuries. The girls were followed for seven years.

During that time, almost 4 percent of the girls developed a stress fracture. Dairy and calcium intake seemed to bear no relationship to the risk of a stress fracture. However, girls with the highest vitamin D intake had a 50 percent lower risk of stress fracture compared with the girls who had the lowest intake. This was especially evident among girls who participated in at least one hour a day of high-impact physical activity. They had a 52 percent decreased risk.