Think your bones stopped growing by the time you finished high school? Think again. Bones constantly remodel themselves throughout life, growing here, thinning there.
In osteoporosis, though, normal bone remodeling goes awry. Bone loss exceeds bone growth, and bones become thin and weak. Osteoporosis affects 10 million Americans, leading to 1.5 million fractures every year.
Osteoporosis medications and physical activity can tip the balance of bone remodeling, preserving bone strength. How does bone remodeling work? What can be done to slow down or reverse bone loss? Read on to learn what you can do to keep your bones healthy and strong.
Bone Remodeling: A Never-Ending Improvement Project
"People think bones are static, but in fact bone is constantly growing and being resorbed," says Mary Zoe Baker, MD, an endocrinologist and professor of medicine at the University of Oklahoma Health Sciences Center in Oklahoma City. "It has to, in order to heal damage and microfractures" that occur with normal wear and tear, says Baker.
The process of bone remodeling is a give-and-take between two opposing forces, replacing old bone with new bone.
- Bone loss (resorption): Special cells called osteoclasts break down bone. They are like a demolition crew. When the signal comes, osteoclasts are recruited to enter the bones and secrete enzymes that break down collagen and minerals. Somehow, they know just when to stop to avoid damaging the bone.
- Bone growth:Special cells called osteoblasts line the surface of bones. In response to signals in the blood, the osteoblasts get to work. They lay down bone, by depositing calcium and phosphate crystals on a scaffolding of collagen.
In healthy bone, the processes of growth and resorption are equalized. Various hormones, including estrogen in women, help keep this balance.
Bone Remodeling Can Go Awry
As it turns out, this delicate balance of bone remodeling can become disrupted as we get older.
"Around menopause in women, and also for some older men, this balance becomes disordered," says Felicia Cosman, MD, clinical director of the National Osteoporosis Foundation. "The amount of bone removed starts to exceed the amount replaced."
As bone resorption exceeds growth, bones lose density and strength, becoming more likely to break.
Osteoporosis Medication Can Restore Balance
"The large majority of these medicines are anti-resorptive medications," Cosman tells WebMD. These drugs slow down bone resorption, so bone growth has time to catch up.
Here are a few facts about several osteoporosis medications:
Bisphosphonates are the most commonly used prescription medications for osteoporosis. There are three major drugs in this family:
Bisphosphonates enter the bones, binding to areas of bone undergoing resorption. When osteoclasts try to dissolve bone coated with the drug, it disrupts the osteoclasts' function. The result? Less bone gets resorbed, and the bone has a better chance to rebuild.
"Bisphosphonates are the most effective medicines we have to treat osteoporosis," says Mary Rhee, MD, MS, an endocrinologist and assistant professor of medicine at Emory University in Atlanta. The key health benefits: increased bone density and reduced risk of fracture.
Calcitonin is a hormone made in the thyroid gland. In animals, calcitonin binds to osteoclasts, preventing bone resorption. The drug preparation of calcitonin is usually made from salmon calcitonin, which is more potent than human calcitonin.
Taken as a medicine, calcitonin slows bone loss, increases bone density, and may relieve bone pain. It is most often used as additional therapy, or when someone cannot tolerate a bisphosphonate. The key health benefit: Reducing the risk of spinal fractures.
Raloxifene is a selective estrogen receptor modulator, or SERM, originally used to treat breast cancer. Now, it’s also approved to prevent and treat osteoporosis. Raloxifene binds to estrogen receptors throughout the body to produce some estrogen-like effects. One effect is prevention of bone resorption.
Doctors typically use raloxifene in addition to other osteoporosis medications, not by itself. Because raloxifene may also reduce the risk of breast cancer, it may be a good medicine for someone with osteoporosis who is also at high risk for breast cancer.
The key health benefit: Increased bone mass and reducing the risk of spinal fractures.
In treating or preventing osteoporosis, calcitriol has shown promise in some studies, but not in others. Also, this drug requires periodic monitoring of calcium levels. Most experts do not recommend calcitriol as a first-line treatment for osteoporosis.
Teriparatide is a prepared form of human parathyroid hormone. This hormone has a tricky effect. Constant high levels of parathyroid hormone cause bone resorption and loss. But intermittent doses of teriparatide cause bone formation.
Teriparatide is the only medicine today proven to stimulate bone growth. It's also proven to prevent fractures. Teriparatide has two main drawbacks: it's extremely expensive, and it must be given as an injection.
Also, when teriparatide is given to women already taking bisphosphonates, bone growth is less than when it's given to a woman as a first-line medicine. "It's nice to have a drug that actually builds bone," says Baker. "But the cost issues [with teriparatide] still need to be worked out." The key health benefit: bone grown and reduced risk of fractures.
Vitamin D and Calcium
You won't see million dollar ad campaigns for these low-tech osteoporosis medicines. But don't let that fool you: osteoporosis experts say vitamin D and calcium are key to preventing and managing osteoporosis.
Every postmenopausal woman should take 1,200 milligrams of calcium a day, according to the National Osteoporosis Foundation. For women or men with osteoporosis, the need is even greater. As Baker puts it, "trying to build bone without adequate calcium and vitamin D is like trying to build a brick wall without the mortar."
Many women have low vitamin D levels but don't know it, according to Rhee. Since vitamin D in normal doses is cheap and risk-free, a good option for most postmenopausal women is to take a combined vitamin D and calcium supplement every day.
Lifestyle Changes Build and Protect Bones
According to Baker, all peri- or postmenopausal women should take positive steps to build and protect bone -- whether or not osteoporosis is present. Tips include:
- Perform weight-bearing exercises. This can be any form of resistance or weight training. This type of exercise increases bone density.
- Make sure you're getting enough calcium and vitamin D, either through diet or supplements.
- Stop smoking! Tobacco increases the risk for osteoporosis, and quitting can reduce the risk.