Can gentle vibration improve bone density and prevent fractures after menopause?
Soon you may be hearing a lot about low-intensity vibration therapy for strengthening bones and reducing the risk of fractures. Two low-intensity oscillating devices designed for home use are coming onto the market, and the Agency for Healthcare Research and Quality (AHRQ), which advises the federal government on health care matters, is expected to issue a report highlighting the evidence as well as the many unanswered questions about this unique approach to bone health.
These low-intensity vibration devices gently stimulate muscle and bone when you stand on them. They are not to be confused with high-intensity, whole-body vibration machines or plates, which are used mainly for exercise training but are sometimes promoted for bone-building. Low-intensity devices provide a tiny fraction of the vibration exposure you would get from the high-intensity machines used by athletes.
An unmet need
Our bones are in constant flux, as old bone is resorbed (broken down) and new bone is created. If breakdown outpaces creation, you may develop low bone density and eventually osteoporosis. Many medications are used in the prevention and treatment of osteoporosis, but only one — teriparatide (Forteo) — stimulates bone growth. (Other medications, including bisphosphonates, work by reducing bone resorption.)
Instead of taking a drug to encourage new bone formation, most women are advised to mechanically stimulate their bones through physical activity, particularly weight-bearing and resistance exercise. When stress is placed on the bones through activities such as running, jumping, and weight lifting, bone cells called osteocytes send signals that activate two other types of bone cells: osteoclasts, which remove damaged areas, and osteoblasts, which form new bone, eventually making the bones denser and stronger.
After menopause, when all women lose bone, the benefits of exercise are usually measured in terms of reduced bone loss rather than actual gain. For example, in a randomized, controlled 12-year German study of postmenopausal women with low bone density, those who participated in a resistance exercise program lost 80% less bone density at the lumbar spine and 45% less in their hips than women who continued their usual level of activity (Osteoporosis International, May 2011).
But for some women, exercise and medication are not enough. As we age, health problems such as joint pain and heart failure may limit our ability to get bone-enhancing exercise. And many women can’t tolerate or prefer not to take osteoporosis medications. The findings on vibration therapy may be particularly important for these women.
An antidote to bed rest?
Prolonged bed rest, which weakens both bones and muscles, may be one culprit in falls among the elderly and people with chronic illness. At Stony Brook University in New York, researchers applied low-intensity vibration to the soles of healthy volunteers undergoing 90 days of strict bed rest. Participants who received the stimulus retained significantly better balance and greater strength in certain muscles involved in maintaining upright posture (Gait & Posture, March 2011).
At Children’s Hospital in Boston, a preliminary study is under way to see whether vibration might reduce bone loss in hospitalized adolescents with anorexia nervosa who are undergoing bed rest as part of their treatment. The teens stand briefly each day on a bedside device delivering low-intensity vibration. If the results are promising, a longer study will be launched to see if vibration could maintain or increase bone density in this vulnerable group.
“Vibratory therapy holds promise not only for adolescents with eating disorders but also for older women who’ve experienced a loss of bone mass related to menopause,” says Dr. Catherine M. Gordon, director of the Children’s Hospital bone health program. “However,” she adds, “until questions are answered regarding safety, all patients should use the platforms under the guidance of a physician.”
How does vibration therapy work?
In low-intensity vibration therapy, you stand on a platform that resembles a bathroom scale while it oscillates up and down a barely noticeable amount. Both the size and speed of the vibration, about 30 cycles per second, are set to match the natural stimulation that occurs as your muscles imperceptibly relax and contract to maintain your posture.
How vibration therapy promotes bone density isn’t well understood, but researchers have suggested several possible explanations. Vibration enhances muscle and bone circulation, boosting the supply of nutrients to these tissues. Research suggests that vibration may also counter an age-related change in bone marrow. Marrow contains certain stem cells that may be converted into bone-building cells (osteoblasts), fat cells, or other cell types, depending on the signals they receive. Laboratory experiments at the University of North Carolina have shown that these stem cells are more likely to become osteoblasts (and less likely to turn into fat cells) when exposed to low-intensity vibration.
Osteoporosis: the evidence
Exposure to low-intensity vibration has been used as a way to prevent bone loss in people whose extreme situations prevent them from performing any weight-bearing exercise whatsoever — for example, patients with spinal cord injuries and children with neurological conditions that impair muscle use. And researchers are looking into it as a way to prevent bone loss in astronauts in zero gravity. But does it work for age-related osteoporosis? We don’t know yet.
According to Dr. Douglas P. Kiel, professor of medicine at Harvard Medical School and a principal investigator with a low-intensity vibration study of adults with low bone density, “There’s a lot of interest but, unfortunately, the evidence is still not substantive enough to draw a firm conclusion about whether low-intensity vibration is good for bone or not.”
In 2010, in an eight-month trial, Australian researchers studied the impact of low- and higher-intensity vibration on hip fracture risk in 47 postmenopausal women (average age 71.5). Women in a control group who continued their usual physical activity lost significant amounts of bone at the spine and hip, but those participating in twice-weekly vibration sessions did not. The researchers found low- and higher-intensity vibration equally effective at preventing bone loss, but they say that caution is warranted.
“Ours was a small study and there will be much more data coming out from other studies. In the meantime, if you want to try vibration therapy, I’d say to stick with the low-intensity machines and follow the manufacturer’s guidelines,” says Dr. Belinda Beck, associate professor in the School of Physiotherapy and Exercise Science at Australia’s Griffith University.
On the other hand, at the 2010 meeting of the American Society for Bone and Mineral Research, researchers from the University of Toronto presented somewhat disappointing results using two speeds of low-intensity vibration in women (average age 60) with osteopenia (low bone density not severe enough to warrant a diagnosis of osteoporosis). After a year of daily use, women exposed to vibration were equal on several measures of bone health to women who used a sham device.
Detecting a benefit may require a longer study. According to Dr. Kiel, even the most potent prescription drugs may take a year or more to increase bone strength.
At Hebrew SeniorLife’s Institute for Aging Research, an affiliate of Harvard Medical School, Dr. Kiel and his colleagues are conducting a three-year randomized trial that may answer many questions about the effects of low-intensity vibration on people with low bone density. Participants — 174 men and women ages 60 and over — are asked to spend 10 minutes a day standing on a research platform, either a sham device or one providing low-intensity vibration. Researchers will compare their outcomes on several measures related to fracture risk, including bone density and structure, balance and falls, bone turnover, and the size and structure of hip muscles. Results are expected in 2012.
In the meantime, it remains unclear who is most likely to benefit from low-intensity vibration, what constitutes an effective dose, and how long it should be pursued. So the AHRQ urges caution in evaluating the purported benefits of vibration for osteoporosis.
“The biology of the bone is very complicated, and it looks like the vibrations have to be just the right frequency and strength to get a good response,” says osteoporosis specialist Dr. Susan Ott, professor of medicine at the University of Washington in Seattle. Dr. Ott fears that if the vibration is too harsh, it might damage bone rather than help prevent fractures. “For now,” Dr. Ott says, “I tell my patients that this looks promising, but they should wait and not rush to try it until the research has shown that it works.”
Coming soon to the market
This fall, two low-intensity vibration devices like those used in osteoporosis research are expected to come on the market. One, the Juvent 1000 (www.juvent.com), was created by prominent vibration researchers — including Dr. Clinton T. Rubin, Distinguished Professor and chair of the Department of Biomedical Engineering atStony Brook University, who conducted pioneering work in the body’s response to vibration. The company, now under different ownership, has resumed production of the device.
The second unit, the Marodyne LIV (low-intensity vibration) Tablet (www.marodyne.com), is an updated device that was developed by Marodyne Medical LLC, a company that includes Dr. Rubin as chief scientific officer. (Dr. Douglas Kiel, whom we quoted in the main article, is a scientific advisor to Marodyne.)
A caution: these devices are expensive (more than $1,600) and not currently reimbursed by insurance.
Most research on whole-body vibration has focused on its risks, in particular, for workers who stand on vibrating platforms, handle vibrating tools, or drive heavy equipment for long hours. According to the National Institute for Occupational Safety and Health, these workers are at high risk for various health conditions, including circulatory and neuromuscular problems, especially lower back pain. Most vibration plates currently on the market are promoted as exercise equipment rather than medical devices and therefore are not subject to FDA review. They commonly produce vibration levels well above the recommended limits for occupational exposure, and they have been associated with various problems, including dizziness, headache, and loss of balance. Serious adverse events, though rare, have also occurred. In 2010, Spanish ophthalmologists reported two cases of women whose intraocular lenses, implanted years earlier during cataract surgery, were dislodged shortly after they worked out on a whole-body vibrating exercise platform. In another report, a woman developed vertigo that lasted for several days following her exercise session.
The manufacturers of vibrating exercise platforms recommend against their use by pregnant women and people who have heart disease, recent wounds or surgery, knee or hip implants, hernia, vertebral or disc defects, diabetes, migraine, epilepsy, tumors, infection, recently implanted metal, or a propensity for blood clots. The AHRQ warns that such high-intensity, whole-body vibration should not be used for the treatment of osteoporosis.
According to the International Organization for Standardization, which uses data based on occupational exposure, the level of vibration delivered by the low-intensity vibration devices used in osteoporosis research is safe for several hours per day — far beyond the length of time recommended for improving bone. But most research using these devices for bone health has excluded people who have serious health problems, can’t stand securely, take bisphosphonates or other bone drugs, or have previous fractures. So the safety of these devices has not been confirmed with respect to those who have the most to gain (and lose) — in particular, frail older people with osteoporosis who are at risk of falling.