Teen runners may be risking long term bone health

Tuesday, 30 August 2011 15:03

A study published in June 2011 (Med Sci Sports Exerc. 2011 Jun;43(6):959-66) reported that female teen runners may not be able to recover from low bone density – underscoring the concern about Athletic Energy Deficit in female athletes. 

In the study, Michelle Barrack and her colleagues in the Graduate Group in Nutritional Biology at the University of California Davis followed 40 teenage long distance runners for three years. They set out to investigate if young female runners starting with low bone mass continue to have low bone mass as they age, putting them at risk of a low peak bone mineral density in adulthood compared with girls who had normal bone mass for their age. The girls averaged about 16 years old when they were recruited and evaluated on a number of factors. Three years later, the researchers measured the girls to determine if any of the factors were associated with long-term changes in bone density.

The researchers collected a number of baseline measurements including menstrual status, amount of training and participation in sports. The girls were grouped by bone mass for age as measured by dual energy x-ray absorptiometry (DXA).

At the follow-up visit, runners gained a slight amount of height, weight, BMI and percent of body fat (0.9 cm ±0.2 cm, 4.7 kg ±0.7 kg, 1.5kg/m2 ±0.2 kg/m2, and 5.6% ±0.6% respectively). There was slight improvement in the prevalence of irregular menstrual cycles from 28.2% and 25.6%. Most notably, 87% of participants with low bone mass (BMD) at baseline had low BMD at follow-up in all of the skeletal sites.

The researchers found that a number of the factors they examined (the amount of training, menstrual function, age, developmental stage, and change in body mass) explained the variability in bone mass between the girls with low bone mass compared to the girls with normal bone mass for their age. They also noted that the girls who started with low bone density mature later and have lower bone mineral content as well as lower bone density.

They concluded that "it appears as though female adolescent runners with low bone mass are more likely to have low BMD after a 3 year follow-up. Thus, "catch-up" growth from adolescence to adulthood does not necessarily occur." 

This finding underscores the importance of the bone building years around puberty (age 9-14) and particularly in young female athletes. Adequate and appropriate nutrition, particularly a diet with calcium and vitamin D, are critical during these years. Girls who do not have a regular menstrual cycle are likely to have Athletic Energy Deficit and may be putting their long term bone heath at considerable risk.