Osteoporosis and the running woman.

O steoporosis or "thin bones" is one of the hottest topics in health care today. It is a skeletal disease characterized by low bone mass and deterioration of bone tissue. Approximately 28 million Americans (80% are women) have osteoporosis, leading to as many as 1.5 million fractures annually. The health care costs from osteoporosis are estimated at 14 billion dollars a year. Some young female runners may be particularly vulnerable to the disease. And if affected, a runner is at even greater risk to suffer fractures as a result of the impact forces inherent in running.

The Bare Bones

Bone strength is determined by a constant balancing act between cells that are forming new bone versus those that are resorbing bone tissue. Bone mass peaks at age 30 after which there is a normal physiologic loss of bone. This process is greatly accelerated in women after menopause due to a loss of estrogen. Therefore, after age 50, women with osteoporosis outnumber men by four to one.

Many factors affect bone mass. Genetic and racial factors are quite significant with white and Asian women much more likely than African Americans to develop osteoporosis. Lifestyle factors such as cigarette smoking, excessive alcohol and caffeine intake promote bone loss. Adequate calcium and vitamin D, on the other hand, helps to preserve bones. Running and other weight-bearing exercise also help maintain bone strength.

The Skinny on Bone Loss

Running benefits bones only up to a point of diminishing returns. Intense exercise (even in young, otherwise estrogen-rich women) can create energy demands that exceed caloric intake. That energy deficit can reduce estrogen production. Loss of estrogen causes menstrual periods to become less regular or to stop completely, mimicking menopause with its potential for bone loss (see "The Female Athlete Triad," Running & FitNews, June 1999). Further complicating the profile for a runner developing this problem, whether due to early loss of periods or the natural onset of menopause, is that high-mileage running puts extra stress on weakening bones. Risk for fractures is greatly increased, especially in the over-trained runner.

Prevention, Diagnosis and Treatment

All post-menopausal women should take supplemental calcium and vitamin D (if sun exposure is limited) in order to prevent osteoporosis. Don't forget that the best prevention of osteoporosis really occurs early in life with adequate childhood and adolescent intake of calcium and exercise because bone density peaks at age 30. At menopause, women should consider hormone replacement (estrogen) or the new designer estrogen Raloxifene to reduce the chance of bone loss.

If you are worried that you may be at risk for osteoporosis, talk to your doctor about a "DEXA scan" or a sonogram technique for calculating your bone density. The DEXA-scan is completely non-invasive; requiring nothing more than a 15-minute rest, fully clothed on an exam table, while a technician performs the scan. Another test uses a CT scan of the heel to measure bone loss. Osteoporosis is diagnosed if your bones are a certain percentage below peak density. Bone mass is also estimated with serial height measurements. If you have lost more than an inch of your normal adult height, osteoporosis is the cause.

If the diagnosis of osteoporosis is made, you can take active steps to increase bone mass and reduce the risk of fracture. Diet, weight-bearing exercise, hormone replacement therapy and other prescription drugs are used to treat osteoporosis. Begin calcium supplementation with 1,500 mg of calcium carbonate and 400 IUs of vitamin D a day The non-hormonal bone stimulant alendronate (Fosamax) is a prescription medication that can play a major role in treating bone loss and reducing fractures.

Finally, don't forget the importance of exercise. As a runner, you are already at an advantage. Running will help to prevent osteoporosis or, if you have already lost significant bone mass, running and strength training can be critical to preserving your bone health. Be aware that running benefits bone mass m the legs, but protecting the rest of the body requires weight lifting or other strength training. The wrists and back are also vulnerable to fractures due to osteoporosis.

If you are an extreme athlete and below average weight, you need to take extra precautions. Increase your nutritional and caloric intake and increase rest and recovery to prevent loss of your periods or to restore them. Research is beginning to show that bone loss due to early osteoporosis may not be fully reversible. Healthy runners enjoy the confidence that prevention of osteoporosis can be added to the list of the great benefits of running. (Richard S. Newman, M.D., F.A.C.O.G. is an obstetrician and gynecologist practicing and running in Washington, DC.)