Damage May Be Permanent : Long-Distance Runners Risk Bone Loss

Evidence is mounting that long-distance running may reduce spinal bone density, resulting in an increased incidence of fractures in later life.

A Cal State San Francisco study of 208 women runners who ran between 20 and 100 miles each week showed that those with menstrual irregularities lasting three years or longer may have experienced irreversible spinal bone loss.

A second study of 26 men by University of Maryland researchers found that the long-distance runners had significantly lower spinal bone mass than non-runners.

The studies prompted members of the American College of Sports Medicine to issue warnings about excessive exercise.

“There are a lot of women who are exercising for fitness and fun,” said Barbara L. Drinkwater, Ph.D., president of the college. “But if they constantly push up until menses stops, then the health benefits from exercise might be negated.”

May Be Irreversible

The San Francisco study found that, compared with female runners with regular menstrual periods, the amenorrheic runners had a 12% to 15% decrease in spinal bone density.

While it was once thought that when athletes ceased excessive exercises their bone density was restored, the California study indicates that bone loss may be permanent if amenorrhea continues for three or more years.

“Amenorrhea if left untreated produces significant and permanent bone loss,” said Dr. C.E. Cann, of Cal State San Francisco.

“Resumption of menses after prolonged amenorrhea doesn’t guarantee restoration of bone loss,” Cann said. “Even runners treated with estrogen therapy didn’t show restoration of bone.”

Although increasing calcium intake in the group of amenorrheic runners resulted in a modest increase in bone density in the first year, Cann said, “it doesn’t go up much after that.”

The researchers placed 85 amenorrheic runners and a group of controls on a diet that included supplements of 1,200 milligrams of calcium a day.

The high calcium intake didn’t increase bone density in the normally menstruating athletes. However, it did increase spinal bone mass in the amenorrheic runners by 3%, Cann said. The effects didn’t appear to increase much beyond the first year.

Although eight women were treated with estrogen, only one woman responded favorably, he said.

The study compared menstrual history, diet, exercise patterns and smoking habits to determine which factors could be used to predict skeletal status.

“Other than menstrual period, there was little effect from the other parameters on bone density,” he said.

Men at Risk Too

The Maryland study compared 13 male long-distance runners with 13 non-runners and found similar effects on spinal bone density.

The runners ran an average of 64 kilometers (about 40 miles) a week while the controls had low levels of exercise or were sedentary

Jo Bilanin, PH.D., of the exercise laboratory at University of Maryland, said the runners had 9.7% less lumbar spine bone density than the non-runners.

There was no difference in age, weight or height. The runners had 29% more oxygen consumption and 54% lower body fat than non-runners. Both groups had similar calcium intake, although the caloric intake was higher in the runners.

“The male long-distance runners had lower bone density, and there was no indication it was due to insufficient calcium intake,” she said.

The Maryland researchers did not test for testosterone levels in the men and therefore aren’t sure whether the lower bone density might be linked to male hormone abnormalities, Bilanin said.

These findings don’t support the idea that weight-bearing exercise in the form of long-distance running is associated with greater bone density, Bilanin said.

Drinkwater predicted that the San Francisco and Maryland studies will stimulate further research into the links between long-distance running and bone density. And she suggested that those exercising for health purposes take note.

Exercise, but keep normal hormone levels, she warned. “If you extend exercise over a period of time without normal hormone levels, then you may never be able to catch up.”