How Serious Is Postmenopausal Osteoporosis?

Susan R. Johnson, M.D.
University of Iowa Hospitals and Clinics

First Published: Summer 2002
Last Revised: February 2003
Peer Review Status: Internally Peer Reviewed

Osteoporosis is a bone disease that may affect all ages and both genders, but most cases occur in postmenopausal women. This presents a serious health threat for postmenopausal women since it predisposes them to an increased risk of bone fracture. Osteoporosis is defined as femoral bone mineral density (BMD) greater than 2.5 standard deviations (SD) below the mean of young, healthy white women.

In the United States, approximately 20%, or 4 to 6 million, of white women aged 50 or older have osteoporosis. Another 35% to 50%, or about 12 to 15 million, have low bone mass, defined as BMD between 1 and 2.5 SD below the mean. Osteoporosis rates are the highest in white women and the lowest in black women. Rates rise from 4% in women 50 to 59 years old to 52% in women 80 years of age and older. Thus, for a 50-year-old white woman, the risk of developing an osteoporotic fracture in her remaining lifetime is nearly 40%. As to fracture location, the lifetime risk for white women is estimated at 17.5% for hip, 15.6% for vertebral, and 16% for a forearm fracture.

In normal bone remodeling, bone resorption is balanced by bone formation. Loss of bone mass occurs when there is prevalence of bone removal over novel bone accumulation. As women move toward midlife and menopause, this imbalance increases resulting in an accelerated bone loss. The most likely explanation for the increased resorption in women versus men after the age of 50 is the drop in estrogen production that characterizes menopause. Specifically, the leading cause for increased bone loss is the decline in circulating levels of 17alpha-estradiol, the hormone that is instrumental for the normal buildup of minerals within the osteocyte meshwork.

Once begun, osteoporosis is irreversible, although it can be slowed down almost to a halt. Women experiencing early menopause, therefore, are at a greater risk of osteoporosis because they will be spending more years without the full protective effect of endogenous estrogen. Risk factors that aggravate osteoporosis include genetics; inadequate intake of calcium and vitamin D throughout life but especially during the second decade of life; low physical activity; smoking; and heavy alcohol consumption.

The National Osteoporosis Foundation recommends institution of therapy to prevent fractures for women with BMD below 2 SD in the absence of additional risk factors, and for women with BMD below 1.5 SD in the presence of fracture risk factors. Women over 70 years of age should be treated regardless of BMD if they have multiple risk factors or fragility fractures. The North American Menopause Society recommends that BMD be measured in all women with medical causes of bone loss and in those who are at least 65 years of age regardless of risk factors. BMD is cost-effective for postmenopausal women aged 50 to 60 years with risk factors or for those beyond the age of 60 to 65 with or without risk factors. Dual-energy x-ray absorptiometry (DXA) is the technical standard for measuring BMD.

Since bone loss occurs most rapidly immediately after menopause, it is critical to assess a woman's risk for future fractures at that time. Anti-resorptive therapy, such as estrogen, can then be started in women at high risk or with low baseline bone density.

Estrogen improves bone mass and significantly reduces vertebral fracture risk. Additional benefits of estrogen include reduction of hot flushes and vaginal dryness, increase in HDL- and reduction of LDL-cholesterol, although it is not yet certain that it protects against cardiovascular events. However, estrogen should be prescribed with caution in women with increased risk of breast cancer and should be combined with a progestogen to protect against increased endometrial cancer. It has been confirmed in many clinical trials that estrogen/progestin initially increases spine BMD 4% to 6% and hip BMD 2% to 3%, and maintains those increases after three years of treatment. Also, estrogen is no longer approved for the treatment of osteoporosis due to the absence of randomized trials related to fracture prevention.

Raloxifene, a selective estrogen receptor modulator, is an agent with estrogen-like effects on bone and lipids, which has an anti-estrogen effect on the breast and no proliferative effect on the endometrium. A side effect of concern is the increased risk of thromboembolism, although the level of risk is the same as for estrogen therapy.

The bisphosphonates, analogues of organic pyrophosphate, which is the endogenous regulator of bone turnover, inhibit bone resorption by osteoclasts. They have been a mainstay of prevention and treatment of osteoporosis for many years but have not been tolerated by all patients; their main side effect is irritation of the upper GI tract.

Combined estrogen and bisphosphonates therapies have an additive effect on postmenopausal bone density. This effect is more pronounced in the lumbar spine and fairly modest at the femoral neck. Because it is not yet known if combined therapy improves the risk of fracture, it should only be used in women who appear to be at very high risk for immediate hip fracture (e.g., elderly frail women on estrogen who have experienced a vertebral fracture or who have very low bone density despite the estrogen.)

Calcitonin is also approved for treatment of osteoporosis, since it inhibits bone resorption yet the reduction in bone turnover is much less than with other anti-resorptive agents. Because of its weaker effect on osteoporosis, calcitonin should be reserved as an alternative for women who cannot or choose not to take one of the other osteoporosis agents.

To sum up, estrogen's role is mainly prevention of osteoporosis, bisphosphonates and raloxifene are used both as prevention and treatment, while calcitonin is prescribed as treatment only. Substitute hormonal therapy for postmenopausal osteoporosis should be backed up by lifestyle approaches, such as a balanced diet rich in calcium and vitamin D, exercise, smoking cessation, alcohol avoidance, and fall prevention. The availability of a range of osteoporotic agents allows for a prevention-treatment plan that is tailored to the individual patient thus maximizing the benefits of the therapy.

See related Provider Textbooks about Obstetrics and Gynecology.

See related Provider Topics Bones, Joints and Muscles, Obstetrics and Gynecology, Osteoporosis, Seniors' Health or Women's Health.

See related Patient Textbooks about Obstetrics and Gynecology.

See related Patient Topics Bones, Joints and Muscles, Obstetrics and Gynecology, Osteoporosis, Seniors' Health or Women's Health.

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