e6-05: Osteoporosis Prevention in Women

Osteoporotic fractures are increasing as the population ages. Age and female sex are major risk factors for osteoporotic fractures. Hip and vertebral fractures are associated with premature mortality. Osteoporosis risk is assessed by measuring bone mineral density (BMD). See also Chapter 26-16. Normal BMD is no lower than 1.0 standard deviation below the mean for young adult women (T score). Osteopenia is defined as BMD between 1.0 and 2.5 standard deviations below the mean for young adults (T score of –1.0 to –2.5), and osteoporosis is defined as a BMD more than 2.5 standard deviations below the young adult mean (T score below –2.5). Severe osteoporosis is defined as either a T score below –2.5 with a fracture or a T score below –3.5.

The World Health Organization's Facture Risk Assessment tool (FRAX, available at https://www.shef.ac.uk/FRAX/tool.jsp) can predict a woman's 10-year risk of having any osteoporotic fracture and the 10-year risk of hip fracture. Risk factors used in the FRAX tool include age, gender, personal history of fracture, parental history of hip fracture, low body mass index, use of oral corticosteroids, secondary osteoporosis, current smoking, and alcohol intake of three or more drinks per day. It can be used with or without BMD. The FRAX tool is particularly helpful in determining which women with osteopenia are most likely to benefit from treatment. Based on the World Health Organization algorithm adopted for the United States, treatment is recommended when there is a 10-year risk of hip fracture of 3% or more or a 10-year risk of a major osteoporotic fracture of 20% or more.

1. Calcium

Although calcium supplementation is routinely recommended, evidence from the Women's Health Initiative showed that calcium supplementation did not reduce fracture risk in healthy postmenopausal women, and other research has highlighted potential risks of calcium supplementation.

2. Calcium plus Vitamin D

The USPSTF recommendations state that the evidence is insufficient (Grade I) to assess the balance of benefits and harms for the combination of vitamin D and calcium for primary prevention of fractures in men or premenopausal women. For noninstitutionalized postmenopausal women, there is insufficient evidence for daily supplementation with more than 400 international units of vitamin D₃ and 1000 mg of calcium; supplementation with less than 400 international units of vitamin D₃ and 1000 mg calcium is not recommended. Recommended calcium intake for women younger than 50 years is 1000 mg/day and for women aged 51 and over, it is 1200 mg/day. Dietary calcium is the preferred route for calcium intake because calcium supplements have been associated with an increased risk of myocardial infarction, although there has not been an increase in either cardiovascular or all-cause mortality. Calcium supplements, if they are taken, can be given as either calcium citrate or calcium carbonate and should be combined with vitamin D. Taking calcium supplementation with meals may reduce the risk of nephrolithiasis. Regular weight-bearing exercise has also been associated with an increase in bone density, although the effect is lost when the exercise is not continued.

3. Vitamin D

Vitamin D is important for bone health. Vitamin D can be given as either D₂ or D₃ formulations. Recommendations are that women aged 70 and younger should consume 600 international units of vitamin D per day, whereas women aged 71 and older should consume 800 international units per day. Individuals with vitamin D deficiency (defined by the National Academy of Medicine as a 25-OH vitamin D less than 20 mg/mL) may require higher doses, although most recommendations for vitamin D supplementation are based on achieving a serum 25-OH vitamin D concentration of 20 mg/mL or more, rather than on a clinical outcome. Whether women should be routinely screened for vitamin D deficiency remains an ongoing question. However, given the association of vitamin D and fractures and falls, checking a 25-OH vitamin D level in women with osteopenia or osteoporosis or at high fall risk is appropriate.

The biggest risk factor for developing osteoporosis is increasing age. Although many women expect to be screened around the time of menopause, routine BMD screening is not recommended until the age of 65. The National Osteoporosis Foundation recommends screening all women aged 65 and older and screening younger postmenopausal women if there is a concern based on their risk-factor profile. The USPSTF recommends screening women aged 65 and older and only screening younger women who are at increased risk for osteoporosis, as determined by a formal clinical risk assessment tool such as the Osteoporosis Self Assessment Tool (OST) or the Simple Calculated Osteoporosis Risk Estimation (SCORE) tool.

In addition, the FRAX tool can be used to calculate 10-year risk of osteoporotic fracture, which can be helpful in decision making about medications. Most guidelines do not specifically address how often a woman should undergo BMD testing. However, decisions about when to rescreen should probably be based on the results of initial screening. Women with normal BMD or mild osteopenia at baseline can be screened less often than women who are near the threshold for osteoporosis.

Treatment is generally recommended in women who have a T score below –2.5, who have already had a fracture, or who have a T score in the osteopenic range but are at high risk for fracture. Treatment options for osteoporosis are described in Chapter 26-16.

FRAX—Fracture Risk Assessment Tool by World Health Organization. https://www.sheffield.ac.uk/FRAX/