When it comes to running, jumping and tumbling teen girls tend to give it all they've got, but overdoing high-impact sports can fatigue the muscles -- leaving them unable to absorb added shock.
When that stress is transferred to the bones it can cause tiny cracks called stress fractures.
Registered Dietitian Kendrin Sonneville of Children's Hospital Boston followed a group of more than 6,700 pre-teen and teen girls for seven years.
She and her colleagues found we should be giving cheerleaders and other athletic girls a "D"...as in Vitamin D.
"For the girls who had the highest intake of Vitamin D, they had half the risk of developing a stress fracture compared with the girls with the lowest Vitamin D intake," she explains.
The girls weren't going overboard with supplements.
They generally got all the Vitamin D they needed through fortified milk and other dairy foods, fatty fish like salmon and tuna, and a modest amount of sun exposure.
Calcium by itself did not reduce the risk.
Dietitians recommend teen girls get 600 international units of Vitamin D a day.
That amounts to two to three glasses of skim milk a day plus a serving of yogurt.
"It is really important to space it out during the day, because if you try to take in all your dairy at once, your body can't absorb it like that," notes registered dietitian Denise Cole.
Prevention is often the best strategy because the best treatment for a stress fracture is rest, which can be a bitter pill to swallow for many of young athletes
Even a tiny bone break as a young teen can lead to long-term health consequences, like an increased risk for osteoporosis -- if the fracture isn't given time to heal.