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It has no symptoms and occurs slowly over the years. Many women have no idea that they’ve suffered bone loss until one day they trip, fall, and fracture a bone. The U.S. Surgeon General estimates that by 2020 half of all Americans could have weak bones due to bone loss. Osteoporosis—the disease resulting from bone loss—causes more than 1.5 million fractures every year, including 300,000 hip fractures, 700,000 vertebral fractures, 250,000 wrist fractures, and more than 300,000 fractures of other bones.

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Though bone loss affects both women and men as they age, women suffer the health consequences in far greater numbers. Of the estimated 10 million Americans who have osteoporosis today, 8 million are women. It’s estimated that one in every two women over 50 will have an osteoporosis-related fracture in her lifetime.2 This article focuses on the risk of bone loss in women.

Although we may think of bone as hard and durable, in fact it is living tissue that grows and changes throughout our lives. Old bone is constantly being removed and new bone formed. In childhood, adolescence, and early adulthood, new bone formation outpaces the removal of old bone. As we age, however, that process reverses.

“As women we reach our peak bone mass between the ages of 25 and 30,” explains Susan Greenspan, MD, director of the Osteoporosis Prevention and Treatment Center and Bone Health Program at the University of Pittsburgh Medical Center. “After that it’s downhill for the bones. For women bone loss often accelerates at menopause, when we lose the protective effect of estrogen.” In the five to seven years after menopause, women may lose up to 20 percent of their bone mass3

Risk Factors

Numerous factors influence a woman’s risk of bone loss, osteoporosis, and fractures.

  • Age. The older you are, the greater your risk.
  • Body size. Small, thin-boned women are at higher risk.
  • Ethnicity. White women and Asian women are at higher risk.
  • Family history. If your mother, grandmother, or sister had osteoporosis, you’re at higher risk.
  • Personal history. Any bone fracture after age 50 increases your risk of osteoporosis.
  • Smoking. In addition to its many other adverse health effects, smoking weakens bones.
  • Diet. Inadequate intake of calcium and vitamin D and excess consumption of alcohol increase your risk of osteoporosis.
  • Inactivity. A sedentary lifestyle weakens bones.
  • Medication use. Long-term use of glucocorticoids and some other medications can promote bone loss.

Maintaining Strong Bones

“The earlier in life women begin to think about preventing bone loss, the better off they will be,” says Dr. Greenspan. “On the other hand, it’s never too late to prevent bone loss from getting worse, either.”

Consuming adequate amounts of calcium and vitamin D is key to maintaining strong bones. The National Academy of Sciences and the National Osteoporosis Foundation (NOF) recommend that adults age 50 and under consume 1,000 mg of calcium daily; for adults over 50, 1,200 mg daily are recommended (see article “Getting Enough Calcium and Vitamin D”).4 

In addition to adequate calcium, it’s important to consume sufficient vitamin D, which your body needs to absorb calcium. Most medical experts recommend a daily intake of between 400 and 800 international units (IU) of vitamin D. The NOF recently updated its recommendation for daily vitamin D consumption by adults 50 and over to between 800 and 1,000 IU.5

Regular weight-bearing exercise is also crucial for maintaining strong bones. “Exercise is good for a lot of things, but it’s also good for the bones—as long as it’s weight-bearing exercise such as walking, jogging, or stair-climbing,” says Dr. Greenspan. Like muscles, bones get stronger the more they are used. Thirty minutes per day of weight-bearing exercise (such as three 10-minute walks) will help keep bones strong.

Helping Children and Teenagers Build Strong Bones

The “tween” and teen years (ages 9 to 18) are crucial for bone building. Teenagers establish 90 percent of their adult bone mass by about age 17.6 The NOF and other health organizations recommend that youth ages 9 to 18 consume 1,300 mg of calcium per day to optimize bone development. “If your bones are maximally strong when you’re young, age-related bone loss will have a less serious impact,” says Catherine H. Van Poznak, MD, a specialist in breast cancer and bone health at the University of Michigan Medical Center in Ann Arbor. “The ideal situation would be for our youth to do everything possible to maximize bone health as their skeleton develops.”

Bone-density Testing

A bone mineral density (BMD) test is like an X-ray of your bones. It usually measures the density of bone at the hip, in the spine, and sometimes in the wrist. The NOF recommends that all women 65 and older get their bone density tested (the test is covered by Medicare). Younger women should be tested if they are at high risk of bone loss (for example, because they smoke, have a family history of osteoporosis, or use medications that promote bone loss). If you break a bone after age 50, talk to your doctor about getting a bone density test.

Bone Loss and Cancer

Cancer survivors have an elevated risk of osteoporosis and fractures.9  A premenopausal woman who goes through chemotherapy may experience early menopause. “She is at risk for bone loss because of the shorter duration of exposure to the bone-preserving effects of estrogen,” explains Dr. Van Poznak.

Breast cancer patients are exposed to additional risk if they are treated with an aromatase inhibitor (AI). Postmenopausal women with estrogen receptor-positive (ER-positive) breast cancer are highly likely to be treated with an AI. These drugs, which include Arimidex® (anastrozole), Aromasin® (exemestane), and Femara® (letrozole), cause bone loss by reducing the amount of estrogen in the body.10

By contrast, in postmenopausal women the drug tamoxifen (Nolvadex®) in effect replaces estrogen in the body and has a protective effect on bone similar to that of estrogen.  In premenopausal women, however, for reasons that are not entirely clear, tamoxifen can cause bone loss.10,11

“It’s important for both patients and their doctors to be aware of the bone-health effects of these drugs,” says Dr. Van Poznak. Patients should have a BMD test before beginning treatment with an AI and annually while on the medication.12  Getting enough calcium, vitamin D, and weight-bearing exercise—important for all postmenopausal women who want to maintain their bone health—is of even greater importance for women taking AIs.

Treatments for Bone Loss

Drugs known as bisphosphonates are often the mainstay of treatment for osteoporosis and low bone density, according to Dr. Greenspan. These drugs, which include Fosamax® (alendronate), Actonel® (risedronate), and Boniva® (ibandronate), work by slowing down the rate at which the body breaks down bone.

Hormone replacement therapy (HRT) is no longer routinely recommended to treat bone loss, says Dr. Greenspan, because two large studies have shown that it increases the risk of heart attack, stroke, and breast cancer.13,14 “But if a woman is on HRT for other reasons—such as to treat menopausal hot flashes—it will prevent the rapid bone loss than can occur around menopause.” All postmenopausal women should discuss the benefits and the risks of HRT with their doctor.

Another option for treating bone loss in postmenopausal women is Evista® (raloxifene), a drug in the same class as tamoxifen. Like tamoxifen, Evista mimics the bone-protective effect of estrogen in the body.

Forteo® (teriparatide) is a drug that builds bone mass; but unlike the bisphosphonates and Evista, which can be taken by mouth, Forteo must be given by injection. In studies of laboratory rats, Forteo caused an increase in the incidence of bone tumors. Because little is known about its long-term effects, the use of Forteo for longer than two years is not recommended.15 “Forteo is usually reserved for patients who have already had a fracture, who have extremely low bone density, or who cannot tolerate other therapies,” says Dr. Greenspan.

Forteo might not be the most appropriate treatment for osteoporosis in breast cancer survivors because of the drug’s association with bone tumors in animals, says Dr. Van Poznak. Women with ER-positive breast cancer who have taken tamoxifen for five years should not take Evista because it could increase their risk of a cancer recurrence.12 HRT is not recommended for breast cancer survivors for the same reason.16

A bisphosphonate may be the best choice to treat bone loss in breast cancer survivors, says Dr. Van Poznak. “These drugs would not be expected to negatively affect the risk of breast cancer recurrence.” Studies show that bisphosphonates can prevent bone loss in women being treated with AIs and women with chemotherapy-induced early menopause.17-19

Other Medications and Conditions That Can Cause Bone Loss

Some health conditions, as well as the medications used to treat them, can cause bone loss as a side effect.

Women who have arthritis or asthma may lose bone mass as a result of avoiding weight-bearing exercise because it’s painful or can trigger an attack. Also, medications often used to treat these conditions—corticosteroids such as prednisone (Deltasone® and Orasone®) and dexamethasone (Decadron® and Hexadrol®)—cause bone loss by inhibiting new bone formation and interfering with the body’s absorption of calcium. According to the American College of Rheumatology, anyone who takes corticosteroids (also called glucocorticoids) for more than three months is at risk of osteoporosis.20  Conditions such as lupus and inflammatory bowel disease may be treated with long-term corticosteroids, as well.

Having an overactive thyroid or parathyroid gland can also interfere with calcium absorption, leading to bone loss. Taking excessive doses of thyroid medication can have the same effect. Celiac disease (gluten intolerance), lactose intolerance, and the eating disorder anorexia nervosa can cause bone loss because the body either can’t absorb calcium or gets insufficient calcium.

Recent studies suggest that two popular classes of drugs—proton pump inhibitors (e.g., Aciphex,® Nexium,® and Prilosec®), used to treat gastrointestinal reflux, and selective serotonin reuptake inhibitors (e.g., Prozac®, Paxil®, and Zoloft®), used to treat depression—may increase the risk of hip fracture, especially when they are taken for a long time.21,22 Further research is needed on the fracture risks posed by these commonly prescribed medications, says Dr. Greenspan.

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16 Holmberg L, Anderson H, HABITS steering and data monitoring committees. HABITS (hormonal replacement therapy after breast cancer—is it safe?), a randomised comparison: Trial stopped. Lancet. 2004;363(9407):453-55.

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