Jan. 27, 2003 -- They seem to be at the peak of health. But young female long-distance runners risk bone loss, a British study confirms.
Running is good for you. It reduces the risk of heart disease, diabetes, and obesity. It once was thought to increase bone density -- but that's not necessarily so. Recent studies show that women who run long distances have lower bone density than women who just sit around. That's not good. Low bone density is a sign of osteoporosis and high risk of bone fracture.
How can this be? That's what a research team led by Melonie Burrows, PhD, lecturer in sport and exercise physiology at the U.K.'s University of East London, tried to find out. They enrolled 52 women runners, age 18-44, in an intensive study. The women ranged from recreational endurance runners who ran only five kilometers a week to elite athletes who ran 70 km a week. The average woman in the study ran eight hours per week and covered 32 km. They were also questioned to evaluate the possible effect of eating too little might have on bone loss.
The result: The women who ran the most had the lowest bone density. Each extra 10 km run per week was linked to 1% to 2% lower bone density. Women who had more muscle lost less bone, but the most muscular women were not those who ran the most. The study appears in the British Journal of Sports Medicine.
"If runners aren't taking on board enough energy, they tend to have bone [loss]," Burrows tells WebMD. "Women must eat properly. Is it the muscle mass that is the main thing to promote bone? When you look at women who play high-impact sports such as gymnastics and rugby, they have very high bone density -- more than runners. So it might be that muscle mass is the predominant factor influencing bone growth."
This makes a lot of sense to Peter W.R. Lemon, PhD, director of the exercise nutrition research laboratory at Canada's University of Western Ontario.
"In our lab, we have found that when female athletes get into serious training, they often undereat," Lemon tells WebMD. "When their food intake and energy expenditure are not matched, women will slow down their metabolism. They are able to exist almost normally on a large energy deficit. But this often leads to nutritional deficiencies. This could lead to loss in bone mass and stress fractures."
When a female athlete overtrains, her estrogen levels drop. This has a very strong effect on bone health. Fortunately, there is a warning signal: Such women have irregular periods or even stop menstruating.
"Don't give up running, and if you are thinking of taking up running, by all means do it," Burrows says. "Just be sure to combine your running with a healthy diet and maintain a regular menstrual cycle. And if you can, add weight training as well."
Burrows takes her own advice: She throws the javelin. Her bone density, she reports, is excellent.
Lemon says that bone and muscle have the same response to weight-bearing exercise: It makes them bigger and stronger. Exercises that stress the bones build bone mass. Simply repeating low-stress exercise seems to have little effect. High-impact exercise is best for building bone strength. Sports like gymnastics, weightlifting, and volleyball apply more stimulation for bone growth than running.
"If you compare running to swimming, running is better for bone," Lemon says. "But running is not as good as strength exercises, where more resistance is applied to the bone."