Harvard Medical School Adviser by the Faculty of Harvard Medical School

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Q:

I've heard about something called vibration therapy, which is supposed to strengthen bones. As a woman in her 60s with borderline osteoporosis, I worry about weak bones and fractures. Can the vibration therapy improve my bone density and protect me from fractures?

A:

There's a reason you're starting to hear about low-intensity vibration therapy for strengthening bones and reducing the risk of fractures. That's because two low-intensity oscillating devices designed for home use are coming onto the market soon.

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. These 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 some athletes.

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 (see illustration).

Many medications can be used to prevent or treat osteoporosis, but only one -- teriparatide (Forteo) -- stimulates bone growth. Instead of taking this drug to boost new bone formation, most women are advised to stimulate their bones by exercising, particularly with weight-bearing and resistance exercises.

Running, jumping and weight lifting puts stress on the bones. As a result of this stress, bone cells called osteocytes send signals that activate two other types of bone cells. Osteoclasts remove damaged areas. And osteoblasts form new bone that eventually makes the bones denser and stronger.

But for some people, 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 people can't tolerate or prefer not to take osteoporosis medications. The findings on vibration therapy may be particularly important in these cases.

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 proposed several possible explanations. Vibration increases the flow of blood to muscles and bones. This boosts the supply of nutrients to these tissues.

Vibration may also protect against 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.

Exposure to low-intensity vibration has been used as a way to prevent bone loss in people who cannot perform any weight-bearing exercise whatsoever. Some examples are 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 low-intensity vibration work for age-related osteoporosis? It's the key to your question, but scientists don't yet know the answer. Research results have been varied and, unfortunately, the evidence is still not substantive enough to draw a firm conclusion about whether low-intensity vibration is good for bone or not.

Most vibration plates currently on the market are promoted as exercise equipment rather than medical devices. That means they are not subject to FDA review. Many devices produce vibration levels well above the recommended limits. They can also cause dizziness, headache and loss of balance.

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. v So the safety of these devices has not been confirmed for people like you who have the most to gain (and lose) -- in particular, older people with osteoporosis who are at risk of falling.

Until researchers learn more about vibration plates, you should focus on the tried and true: Do the exercises that are right for you and get the vitamin D (typically 800-1000 IU a day) and calcium (1200 mg a day for women over 51) you need for strong bones. Ask your doctor if a prescription medication for osteoporosis may be helpful. And keep abreast of new research developments that may (or may not) shake up traditional advice about bone health.

(Submit questions to harvard_adviser@hms.harvard.edu.)

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