INTRODUCTION — Osteoporosis is a common bone disorder characterized by a progressive decrease in bone density and mass. As a result, bones become thin, weakened, and easily fractured. It is estimated that more than 1.3 million osteoporosis-associated (or "osteoporotic") fractures occur every year in the United States, primarily of bone within the vertebral column, the hip, and the forearm near the wrist. (See "Patient information: Osteoporosis causes, diagnosis, and screening").
Osteoporosis is the result of accelerated bone loss due to an imbalance between the normal breakdown (resorption) and replacement (formation) of bone. In most patients, such bone loss is largely menopause- and/or age-related. Bone mass naturally declines as people age (ie, beginning at about age 35 years); in addition, women are particularly at risk for osteoporosis following menopause due to declining production of the female hormone estrogen, which helps to maintain bone mass.
Multiple therapies are available that may prevent bone loss and treat low bone mass. However, the first step in preventing or treating osteoporosis is to eat the right foods, particularly those that provide calcium, a mineral essential for bone strength, and vitamin D, which aids in calcium break down and absorption. (See "Patient information: Osteoporosis prevention and treatment").
BENEFITS — Good nutrition is important at all ages, from infants to the elderly, to keep the bones healthy. In some studies in postmenopausal women, taking calcium reduced bone loss and decreased the risk of recurrent vertebral fractures.
In addition, consuming calcium during childhood (eg, in milk) can lead to higher bone mass in adulthood. The increase in bone mineral density is important in modifying future fracture risk. The risk for most osteoporotic fractures increases as the bone density decreases. This means, the lower the bone mass, the greater the tendency to fracture. Calcium also has benefits in other body systems by reducing blood pressure and cholesterol levels.
Calcium balance in the body refers to the balance between calcium that is taken in (eaten) and calcium that is excreted (eg, in urine). Not surprisingly, the less calcium an individual takes in, the more negative the calcium balance. By increasing one's calcium intake, calcium balance can become more positive.
Multiple investigations have supported the importance of calcium intake, demonstrating that adequate calcium reduces bone loss in adults. As examples: Two studies demonstrated that postmenopausal women whose calcium intake was less than 400 or 750 mg/day had significant reductions in bone loss when supplemented with calcium as opposed to placebo (an inactive substance). In women over age 60 years with a low calcium intake who had preexisting spinal (vertebral) fractures, calcium supplementation reduced the incidence of additional vertebral fractures compared to placebo and stopped detectable bone loss within the forearm (over four years of follow-up). One study demonstrated that calcium supplementation in postmenopausal women was associated with a small but significant increase in bone density.
Calcium and vitamin D supplements have been shown to help prevent tooth loss in the elderly.
RECOMMENDATIONS — As mentioned above, adequate calcium intake can result in positive calcium balance and a reduction in the rate of bone loss; it is less clear if adequate calcium intake decreases the risk of bone fractures. However, most clinicians recommend calcium supplementation for patients with a low calcium intake since it appears to reduce bone loss.
Daily calcium intake should be at least 1000 mg in premenopausal women and men, and 1500 mg in postmenopausal women who do not take estrogen. The total daily calcium intake should not routinely exceed 2000 mg due to the possibility of adverse effects.
Persons who cannot get enough calcium from dietary sources should speak with their clinician for specific recommendations about the type, dose, and timing of calcium supplementation (show figure 1). The following are general guidelines Calcium carbonate is an effective and inexpensive form of calcium. It is best absorbed with a low-iron meal (such as breakfast). Calcium citrate (eg, Citracal®) may be recommended for elderly people who absorb calcium carbonate less readily (because of less acid in the stomach). Chewable preparations of calcium carbonate (eg, Viactiv®, Tums®) or calcium citrate (Citracal®) are preferred since many natural calcium carbonate preparations (eg, bone meal, oyster shells) do not dissolve well. In addition, these preparations can be contaminated with lead and/or mercury. Calcium supplements should be taken in divided doses. Doses above 500 mg are not absorbed as well as smaller doses. Calcium supplementation is not an alternative to other osteoporosis treatments. Calcium is less effective than other treatments, including hormone replacement, bisphosphonates (eg, risedronate [Actonel®] and alendronate [Fosamax®]), and raloxifene (Evista®) in slowing bone loss in postmenopausal women. Hormone therapy is recommended only for women with certain menopausal symptoms. However, calcium had additive benefits when used along with other treatments. (See "Patient information: Osteoporosis prevention and treatment").
Underlying gastrointestinal diseases — Patients with impaired absorption of nutrients from the gastrointestinal tract (malabsorption) may have higher than normal calcium requirements due to reduced calcium absorption. In such cases, a healthcare provider can help to determine the appropriate level of calcium supplementation.
Medications — Administration of certain medications may influence calcium balance, such as drugs that promote the excretion of urine (diuretics). As an example, so-called "loop diuretics" increase the excretion of calcium; however, thiazide diuretics may lead to reduced levels of calcium in the urine, potentially helping to protect against possible bone loss and kidney stones (see below). Therefore, it is important for patients to tell their physicians and pharmacists about all medications they are taking so that any possible interactions with calcium can be identified.
DETERMINING CURRENT CALCIUM INTAKE — The primary sources of calcium within the diet include milk and other dairy products, such as hard cheese, cottage cheese, or yogurt, as well as green vegetables, such as spinach (show table 1). A simple way to estimate one's daily intake of dietary calcium is to multiply the number of dairy servings consumed each day by 300 mg. One serving equals 8 oz of milk or yogurt, 1 oz of hard cheese, 16 oz of cottage cheese, or 2 cups of broccoli.
Many experts recommend calcium supplementation rather than dietary changes for individuals with inadequate calcium intake. Evidence suggests that calcium is as well absorbed from supplements as from whole milk. In addition, calcium supplements were used in the studies cited above that demonstrated benefits from increased calcium intake. Therefore, it is likely that calcium supplements are just as effective as calcium in dairy products. However, calcium absorption from vegetables (eg, spinach) is less than that from dairy products.
IMPORTANCE OF VITAMIN D — In addition to calcium, vitamin D is important in the prevention and treatment of osteoporosis. Vitamin D is normally synthesized in the skin after exposure to sunlight. It can also be ingested from dietary sources. Vitamin D deficiency occurs as a result of decreased intake or absorption or from reduced exposure to the sun. Vitamin D levels decline with age and with decreased sun exposure, especially in the winter. In temperate areas such as Boston and Edmonton, for example, production of vitamin D by the skin virtually ceases in winter.
Multiple clinical trials have proven that vitamin D decreases bone loss and lowers fracture rates, especially in older men and women. The current recommendation for daily intake of vitamin D in adults is at least 800 International Units (IU). Lower levels of vitamin D are not as effective while doses higher than 2000 IU per day can be toxic. Milk is the best source of dietary vitamin D, with approximately 100 IU per cup.
A vitamin D supplement is recommended for all patients with osteoporosis whose dietary intake of vitamin D is below 400 IU/day. A daily multivitamin is both convenient and economical, and has the added advantage of providing other vitamins. Alternately, patients may take a calcium supplement that contains Vitamin D.
SIDE EFFECTS — Side effects related to calcium include constipation and indigestion (dyspepsia).
Previous data suggested that calcium supplementation might be associated with weight loss, though two large, randomized trials reported no significant effect of calcium supplements (1000 mg/day) on body weight.
Concern that high dietary calcium increases the risk of kidney stones in otherwise healthy patients appears to be unfounded since the incidence of stone formation appears to be reduced in both men and women who consume high amounts of dietary calcium.
WHERE TO GET MORE INFORMATION — Your healthcare provider is the best source of information for questions and concerns related to your medical problem. Because no two patients are exactly alike and recommendations can vary from one person to another, it is important to seek guidance from a provider who is familiar with your individual situation.
This discussion will be updated as needed every four months on our web site (www.patients.uptodate.com). Additional topics as well as selected discussions written for healthcare professionals are also available for those who would like more detailed information.
A number of web sites have information about medical problems and treatments, although it can be difficult to know which sites are reputable. Information provided by the National Institutes of Health, national medical societies and some other well-established organizations are often reliable sources of information, although the frequency with which they are updated is variable. National Library of Medicine
(www.nlm.nih.gov/medlineplus/healthtopics.html)
Osteoporosis and Related Bone Diseases National Resource Center (ORBD-NRC)
1232 22nd Street, NW
Washington, DC 20037-1292
Phone: (202) 223-0344
Toll-free: (800) 624-BONE (2663)
TTY: (202) 466-4315
E-mail: orbdnrc@nof.org
(www.osteo.org)
National Osteoporosis Foundation
1232 22nd Street NW
Washington, DC 20037-1292
Phone: (202) 223-2226
E-mail: patientinfo@nof.org
(www.nof.org)
Osteoporosis Society of Canada
33 Laird Drive
Toronto, Ontario M4G 3S9
Phone: (800) 463-6842
(www.osteoporosis.ca/)
The Hormone Foundation
(www.hormone.org/public/osteoporosis.cfm, available in English and Spanish)
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2. Aloia, JF, Vaswani, A, Yeh, JK, et al. Calcium supplementation with and without hormone replacement therapy to prevent postmenopausal bone loss. Ann Intern Med 1994; 120:97.
3. Cook, JD, Dassenko, SA, Whittaker, P. Calcium supplementation: Effect on iron absorption. Am J Clin Nutr 1991; 53:106.
4. Curhan, GC, Willett, WC, Speizer, FE, et al. Comparison of dietary calcium with supplemental calcium and other nutrients as factors affecting the risk for kidney stones in women. Ann Intern Med 1997; 126:497.
5. Dawson-Hughes, B, Harris, SS, Krall, EA, Dallal, GE. Effect of calcium and vitamin D supplementation on bone density in men and women 65 years of age or older. N Engl J Med 1997; 337:670.
6. Ross, EA, Szabo, NJ, Tebbett, IR. Lead content of calcium supplements. JAMA 2000; 284:1425.
7. Heaney, RP. Lead in calcium supplements: cause for alarm or celebration?. JAMA 2000; 284:1432.
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