Aug. 9, 2001 -- A new animal study suggests that gentle mechanical forces can improve bone growth. If the findings hold true in humans, this may offer a new way to prevent osteoporosis. The study was published in the Aug. 9 issue of Nature.
"Exercise may prevent osteoporosis, but we always thought it had to be short bursts of intense activity," lead researcher Clinton Rubin, PhD, tells WebMD. "Our work now shows that even very low levels of mechanical stimulation promote bone growth."
In his study, adult female sheep treated with gentle vibration to their hind legs for 20 minutes a day, 5 days a week had 30% more bone in their legs than did untreated animals after 1 year.
"We're trying to trick a 68-year-old skeleton into thinking it's a 23-year-old skeleton," says Rubin, professor and chair of biomedical engineering and director of the Center for Biotechnology at the State University of New York in Stony Brook.
"Although antiresorptive drugs like Fosamax have FDA approval in treatment of osteoporosis, our work shows that bone is also very responsive to mechanical stimuli," says Rubin. "The conventional wisdom was that loads needed to stimulate a metabolic response in bone were at least twice that seen in walking. Our work shows that the magnitude of forces needed to produce a dramatic increase in trabeculated bone is much less."
Without the force of gravity pulling on the skeleton, astronauts lose bone at the rate of 0.2% per month, says Rubin. Conversely, a professional tennis player may have 30% more bone on his playing arm. "The skeleton is a smart material accommodating the demands placed on it," says Rubin.
"The possibility of a nonpharmacological way to increase bone density is very exciting," Robert Marcus, MD, tells WebMD after reviewing the study. "Although these are preliminary findings, they should be applicable to clinical situations once appropriate studies are done. There is no a priori reason to think that results wouldn't be similar in humans, because you're dealing with universal characteristics of bone."
"While exercise is clearly beneficial to prevent postmenopausal osteoporosis, it does not substitute for adequate attention to diet and hormonal status. There are no clinical trials showing that exercise prevents osteoporotic fractures," says Marcus, professor of medicine at Stanford University.
"Although there are FDA-approved drugs to prevent bone loss in menopause, most women probably don't want to take a drug every day for 40 years," Rubin says.
Case in point is two patients with severe osteoporosis in Bangor, Maine, followed by Cliff Rosen, MD. They cannot exercise or take any drugs due to comorbidities but seem to be responding to gentle mechanical stimulation. Rosen is former chief of medicine at Bangor University School of Medicine and president of the American Society of Bone and Mineral Research.
Rubin and colleagues are already testing the effects of gentle vibration on bone loss in 64 postmenopausal women. Half of them stand on a vibrating platform resembling a bathroom scale for 20 minutes, 5 days a week, while the other half stand on a similar device that does not vibrate. The forces involved are so gentle that the women can't tell whether or not the platform is vibrating. Rubin says it's still too early to be sure how his study is turning out, but calls it "very encouraging."
"We're very excited about the animal data, the very preliminary human data, and even more excited about the theory that gentle mechanical stimulation encourages new bone growth," says Rosen.
"The absolute worst thing you can do to the skeleton is to put it to rest," Marcus says. "While active people seem to have less risk of brittle bones as they get older, not every woman who goes through the change feels like running a marathon."