Get answers to your Osteoporosis, Metabolic Bone & Mineral Disorders questions.
Osteoporosis is a skeletal disease in which bones become brittle and prone to fracture. In other words, the bone loses density. Osteoporosis is diagnosed when bone density has decreased to the point where fractures occur with mild stress.
Until a healthy adult is around age 40, the process of breaking down and building up bone by cells called osteoclasts and osteoblasts is a nearly perfectly coupled system, with one phase balancing the other. As a person ages, or in the presence of certain conditions, this system breaks down and the two processes become out of sync. The reasons why this occurs during aging are not clear, but declining levels of sex hormone are one factor. Some individuals have a very high turnover rate of bone, some have a very gradual turnover, but the breakdown of bone eventually overtakes the build-up.
The Function of Bones. The skeleton has a dual function:
The skeleton holds 99% of the body‚ ' s calcium. The remaining 1% circulates in the blood and is essential for crucial bodily functions, ranging from muscle contraction to nerve function to blood clotting.
Bone Turnover: the Breakdown and Growth of Bones. Like other organs in the body, bone tissue is constantly being broken down and reformed again. This turnover is necessary for growth, for repair of minor damage that occurs from everyday stress, and for the maintenance of a properly functioning body. Two essential cells are involved in this process:
Each year, about 10 - 30% of the adult skeleton is remodeled in this way. The balance of bone build-up (formation) and break down (resorption) is controlled by a complex mix of hormones and chemical factors. If bone resorption occurs at a greater rate than bone build up, your bone loses density and puts you at risk for osteoporosis.
In women, estrogen loss after menopause is associated with rapid resorption and loss of bone density. This group, then, is at highest risk for osteoporosis and therefore for fracture.
There are two primary kinds of osteoporosis:
What determines the existence of osteoporosis, of either type, is the amount of calcium left in the skeleton and whether it places a person at risk for fracture. Someone who has exceptionally dense bones to begin with will probably never lose enough calcium to reach the point where osteoporosis occurs, whereas a person who has low bone density could easily develop osteoporosis despite losing only a relatively small amount of calcium.
Secondary osteoporosis is caused by other conditions, such as hormonal imbalances, diseases, or medications (such as corticosteroids or anti-seizure drugs).
Ebeling PR. Clinical practice. Osteoporosis in men. N Engl J Med. 2008; 358(14): 1474-82.
Greenspan SL, Bone HG, Ettinger MP, Hanley DA, Lindsay R, Zanchetta JR, et al. Effect of recombinant human parathyroid hormone (1-84) on vertebral fracture and bone mineral density in postmenopausal women with osteoporosis: a randomized trial. Ann Intern Med. 2007;146(5): 326-39.
Greenspan SL, Nelson JB, Trump DL and Resnick NM. Effect of once-weekly oral alendronate on bone loss in men receiving androgen deprivation therapy for prostate cancer: a randomized trial. Ann Intern Med. 2007;146(6): 416-24.
Heckbert SR, Li G, Cummings SR, Smith NL, Psaty BM. Use of alendronate and risk of incident atrial fibrillation in women. Arch Intern Med. 2008;168(8):826-31.
Kothawala P, Badamgarav E, Ryu S, Miller RM and Halbert RJ. Systematic review and meta-analysis of real-world adherence to drug therapy for osteoporosis. Mayo Clin Proc. 2007;82(12): 1493-501.
MacLean C, Newberry S, Maglione M, McMahon M, Ranganath V, Suttorp M, et al. Systematic review: comparative effectiveness of treatments to prevent fractures in men and women with low bone density or osteoporosis. Ann Intern Med. 2008;148(3): 197-213.
National Osteoporosis Foundation. Clinician's Guide to Prevention and Treatment of Osteoporosis -- 2008. Washington, DC.
Qaseem A, Snow V, Shekelle P, Hopkins R Jr., Forciea MA and Owens DK. Pharmacologic treatment of low bone density or osteoporosis to prevent fractures: a clinical practice guideline from the American College of Physicians. Ann Intern Med. 2008;149(6): 404-15.
Tang BM, Eslick GD, Nowson C, Smith C, Bensoussan A. Use of calcium or calcium in combination with vitamin D supplementation to prevent fractures and bone loss in people aged 50 years and older: a meta-analysis. Lancet. 2007 Aug 25;370(9588):657-66.
© 2011 University of Maryland Medical Center (UMMC). All rights reserved.
UMMC is a member of the University of Maryland Medical System,
22 S. Greene Street, Baltimore, MD 21201. TDD: 1-800-735-2258 or 1.866.408.6885