Too Much Exercise? What Every Woman Athlete Should Know About Osteoporosis

On just about any short list of how to prevent osteoporosis, you are likely to see the importance of calcium, Vitamin D, and regular exercise. But in some cases, devotion to working out - especially when paired with an overly stringent dietary regimen - can actually contribute to premature bone loss and even early osteoporosis, especially for women.

This issue has received increased attention in recent years as women's opportunities in high school and college sports have diversified tremendously. As more women than ever are committing to physical fitness and rigorous training routines, it sometimes becomes considered the norm to develop irregular periods or stop menstruating altogether.

While many women miss a period at some time or another, amenorrhea - or an absence of regular periods - may be a symptom that the body is undergoing an unhealthy process. Women athletes who do not eat enough to compensate for energy depleted in their workouts may not have sufficient bodily resources available to produce estrogen. The hormone is necessary for a normal menstrual cycle as well as building and maintaining bone mass.

In a recent article in the American Journal of Clinical Nutrition, PhD candidate Michelle Barrack, MS, of the graduate group in Nutritional Biology at the University of California-Davis, uses the term "dietary restraint" in her research on the physical impact of eating habits on high school cross-country runners. She and her colleagues concluded that young endurance runners who limit their food intake may be putting themselves as risk of weak bones as early as their teenage years.

Even when adjusting for factors such as age and body mass index, those girls who practiced elevated dietary restraint - 16 days or more in the past month of habits including long waiting periods between meals and purposeful restriction of calories or serving size - had the lowest bone mineral density in their lumbar spine. There was also a tendency to have irregular menstrual periods.

"Young runners, given the high energy expenditure associated with the sport of endurance running, may need to be more diligent than a moderately active girl about consuming adequate energy and other bone building nutrients," Barrack wrote in an email discussing her research, which is based on a questionnaire the subjects completed, along with a dual-energy X-ray absorptiometry (DXA) bone scan and height and weight measures. "This may be most important in young adolescent runners because they are still in a growth and developmental period where they should be gaining about 40% of their adult bone mass," Barrack notes.

Nutrition is a key part of preserving one's bone mass, and athletes must consume enough calories to support their heightened energy expenditure along with an adequate intake of particular nutrients. While the National Osteoporosis Foundation recommends for adults under 50 about 1000 mg of calcium and 400-800 IU of Vitamin D daily, some experts recommend additional calcium - about 1500 mg total daily - for those who exercise heavily, since some calcium is lost in sweat.