Heredity may factor into girls' stress fractures

By Amy Norton

NEW YORK (Reuters Health) - Physically active teenage girls may face an increased risk of stress fractures if they have a family history of osteoporosis, a new study suggests.

Stress fractures are tiny cracks that form in the bones due to repeated high impacts, most often in the lower leg, feet or spine. Certain sports, like basketball and gymnastics, may leave athletes particularly vulnerable to stress fractures.

The new study, published in the journal Pediatrics, suggests that heredity is also important.

Of the 168 teenage girls and young women in the study, those who'd suffered a stress fracture were three times more likely to have a family history of osteoporosis or osteopenia.

Osteopenia refers to abnormally low bone mass, while osteoporosis is a brittle-bone disease that raises the risk of fractures.

It's not clear whether an inherited low bone density explains the link, according to the study authors. Study participants with stress fractures had their bone mineral density measured, but their fracture-free peers did not.

However, girls who suffered the injury did, on average, have a lower-than-expected bone density for their age, said lead study author Dr. Keith J. Loud of Akron Children's Hospital, Ohio. It's "reasonable to conclude" that inherited low bone mass is partially responsible for the higher stress fracture risk, Loud told Reuters Health.

The study compared a group of girls and young women ages 13 to 22 who'd suffered a stress fracture with a group of similar, highly active females with no stress fracture history. All study participants answered questions on their family history of osteoporosis and osteopenia, as well as their intakes of calcium and vitamin D, smoking habits and any menstrual irregularities -- all of which may affect bone density.

Only family history turned out to be independently linked to stress fracture risk.

More studies are needed to confirm the findings, according to the researchers. Nonetheless, the results suggest that girls who sustain stress fractures need further evaluation of their bone health, Loud said. Those with a family history of osteoporosis or osteopenia might benefit from having a bone density measurement at a center appropriate for their age, he noted.

The findings do not mean, however, that girls with a history of stress fracture or a family history of bone thinning should avoid physical activity, according to Loud.

"In fact, we would advocate the opposite," he said, because higher-impact exercise helps build bone mass.

Loud hopes future research will define training "thresholds" beyond which stress fracture risk climbs significantly. His team's work so far suggests that this threshold may be 16 to 20 hours of exercise per week.

SOURCE: Pediatrics, August 2007.