Bone mineral density (BMD): Bone mineral density (BMD) is a measurement of the amount of calcium in the bones. Various diagnostic tests exist to determine BMD in individuals susceptible to osteoporosis, such as dual-energy X-ray absorptiometry or DEXA. The National Osteoporosis Foundation recommends a bone density test in women if they are not taking estrogen and any if the following conditions apply: they are taking medications such as corticosteroids (prednisone (Deltasone®) that can cause osteoporosis; they have type 1 diabetes, liver disease, kidney disease, or a family history of osteoporosis; they experience early menopause; they are postmenopausal (older than 50) and have at least one risk factor for osteoporosis; and if they are postmenopausal (older than 65) and have never had a bone density test. Doctors do not generally recommend osteoporosis screening for men because the disease is less common in men than it is in women.

Dual-energy X-ray absorptiometry (DEXA): DEXA is the most accurate way to measure BMD. DEXA uses two different x-ray beams to estimate bone density in the spine and hip. Strong, dense bones allow less of the x-ray beam to pass through them. The amounts of each x-ray beam that are blocked by bone and soft tissue are compared to each other. DEXA can measure as little as 2% of bone loss per year. It is fast and uses very low doses of radiation but is more expensive than ultrasound testing. Single-energy x-ray absorptiometry (SXA) uses one x-ray beam and may be used to measure heel and forearm bone density. SXA is not used as often as DEXA due to less accuracy.

The results of the DEXA test are scored in comparison to the BMD of young, healthy individuals, resulting in a measurement called a T-score. If the T-score is -2.5 or lower, the individual is considered to have osteoporosis and therefore at high risk for a fracture. T-scores between -1.0 and -2.5 are generally considered to show osteopenia. The risk of fractures generally is lower in individuals with osteopenia when compared with those with osteoporosis but, if bone loss continues, the risk for fracture increases.

Peripheral dual-energy X-ray absorptiometry (P-DEXA): Peripheral dual-energy X-ray absorptiometry (P-DEXA) is a type of DEXA test. P-DEXA measures the density of bones in the arms or legs, such as the wrist. P-DEXA cannot measure the density of the bones most likely to break, such as the hip and spine. P-DEXA machines are portable units that can be used in a doctor's office. P-DEXA also uses very low doses of radiation, and the results are ready faster than standard DEXA measurements. P-DEXA is not as useful as DEXA for finding out how well medicine used to treat osteoporosis is working. P-DEXA may be used in less serious cases of osteoporosis.

Dual photon absorptiometry (DPA): Dual photon absorptiometry (DPA) uses a radioactive substance to measure bone density. The radioactivity passes through the body similar to an x-ray. DPA can measure BMD in the hip and spine. DPA also uses very low doses of radiation but has a slower scan time than the other methods.

Quantitative ultrasound: Ultrasound uses sound waves to measure BMD, usually in the heel. If results from an ultrasound test find low bone density, DEXA is recommended to confirm the results. Machines pass the sound waves through air and some pass them through water. Ultrasound is quick, painless, and does not use potentially harmful radiation like X-rays. One disadvantage of ultrasound is it cannot measure the density of the bones most likely to fracture (the hip and spine) from osteoporosis.

Quantitative computed tomography (QCT): Quantitative computer tomography (QCT) is a type of computed tomography scan that measures the density of a bone in the spine (vertebra). A form of QCT called peripheral QCT (pQCT) measures the density of bones in the arms or legs, usually the wrist. QCT is not usually used because it is expensive, uses higher radiation doses, and is less accurate than DEXA, P-DEXA, or DPA.

X-rays: X-rays are low doses of radiation that are used to create an image of a body part, organ, or bodily system on film paper or fluorescent screens. X-rays show the alignment of the spine and may reveal degenerative joint disease, fracture, or tumor. X-rays cannot determine BMD, but can determine if a fracture has occurred.

In the early stages of bone loss, there usually is no pain or symptoms. Once bones have been weakened by osteoporosis, signs and symptoms may include: back pain, which can be severe with a fractured or collapsed vertebra; loss of height over time, with an accompanying stooped posture; and fracture of the vertebrae, wrists, hips, or other bones.

While limb fractures (such as wrist or hip) are obvious, spine fractures can be more difficult to diagnose. Spinal fractures might either be painless, or if there is pain, a person may not know it is caused by a fracture because there are so many different causes of back pain. More obvious signs of spine fractures are loss of height and development of kyphosis or a curved upper back, sometimes called a dowagers hump.

Fractures: Fractures are the most frequent and serious complication of osteoporosis. Fractures often occur in the spine or hips, bones that directly support weight. Hip fractures, the second most common type of osteoporotic fracture, usually result from a fall. Although most individuals do relatively well in recovery with modern surgical treatment, hip fractures can result in disability and even death from postoperative complications, especially in older adults. Wrist fractures from falls are also common. Complications from osteoporotic fractures include chronic pain (neck, lower back), compressed or collapsed vertebra, disability, depression, limited activity, dowager's hump, stooped posture, and loss of height.

The strength of bones depends on their size and density. Bone density depends in part on the amount of calcium, phosphorus, boron, and other minerals that bones contain. When bones contain fewer minerals than normal, they are less strong and eventually lose their internal supporting structure. Genetic and environmental factors, such as diet and exercise, also affect bone strength.

There are many reasons that bone becomes less dense than normal. Bone is continuously changing. New bone is made and old bone is broken down in a process called remodeling, or bone turnover.

A full cycle of bone remodeling takes about two to three months. When an individual is young, the body makes new bone faster than it breaks down old bone, and bone mass increases. Individuals reach their peak bone mass in the mid-30s. After that, bone remodeling continues, but slightly more bone is lost than is gained. In women at menopause, when estrogen levels drop, bone loss increases dramatically. Although many factors contribute to bone loss, the leading cause in women is decreased estrogen production during menopause.When women go through menopause, their estrogen levels drop to one-third of what these levels were during the childbearing years. Estrogen increases bone density by helping to block bone resorption.

The risk of developing osteoporosis depends on how much bone mass was attained between ages 25 and 35 (peak bone mass) and how rapidly the individual loses it later. The higher the peak bone mass, the more bone the individual has and less likely to develop osteoporosis as they age and less likely to suffer major bone loss. Not getting enough vitamin D and calcium in the diet and enough exercise may lead to a lower peak bone mass and accelerated bone loss later in life.

Gender: Fractures from osteoporosis are about twice as common in women as they are in men. Although women are four times more likely than men to develop the disease, men also suffer from osteoporosis. Women develop osteoporosis more often because they start out with lower bone mass and tend to live longer. They also experience a sudden drop in estrogen at menopause that accelerates bone loss. Slender, small-framed women are particularly at risk. Men who have low levels of the male hormone testosterone also are at increased risk. From age 75 years on, osteoporosis is as common in men as it is in women.

It is estimated that around 40% of U.S. Caucasian women and 13% of U.S. Caucasian men aged 50 years and older will experience at least one fracture due to bone loss in their lifetime. It is also estimated that in the United States, 54% of postmenopausal Caucasian women are osteopenic and 30% are osteoporotic, and by the age of 80, 27% of Caucasian women are osteopenic and 70% are osteoporotic.

Age: Bones weaken during normal aging in a process called resorption. As individuals age, whether male or female, there is an average loss of 0.5% bone mass every year after age 50.

Race: Caucasians and Southeast Asians are at the greatest risk of osteoporosis. African American and Latino men and women have a lower but still significant risk of osteoporosis-related fractures.

Family history: Osteoporosis is, in part, hereditary. Having a parent or sibling (brother or sister) with osteoporosis puts the individual at greater risk, especially if the individual also has a family history of bone fractures. An individual with a family member who has osteoporosis has a 50-85% increased risk of developing osteoporosis.

Frame size: Men and women who are exceptionally thin or have small body frames tend to have higher risk because they may have less bone mass to draw from as they age.

Smoking: The impact of cigarette smoking on bone health is not well understood. Smoking may cause a decrease in bone density due to smoking itself or to other risk factors, such as general health. Smokers are usually thinner than nonsmokers, tend to drink more alcohol, may be less physically active, and have poor diets. Women who smoke also tend to have an earlier menopause than nonsmokers. These factors place many smokers at an increased risk for osteoporosis apart from their tobacco use.

In addition, most studies on the effects of smoking suggest that smoking increases the risk of having a fracture. Results have found that the longer an individual smokes and the more cigarettes consumed, the greater the risk of fracture in old age. Smokers who fracture may take longer to heal. Significant bone loss has been found in older women and men who smoke. Studies suggest second-hand smoke exposure during youth may increase the risk of developing low bone mass. Also, women who smoke often produce less estrogen and tend to experience menopause earlier than nonsmokers. Smoking cessations appears to reduce the risk of low bone mass and fractures.

Estrogen levels: The longer a woman is exposed to estrogen, the lower her risk of osteoporosis. Women have a lower risk if they have a late menopause or they began menstruating at an earlier than average age. However, a history of abnormal menstrual periods, experiencing menopause earlier than the late 40s, or having the ovaries surgically removed before age 45 without receiving hormone therapy may also increase the risk of developing osteoporosis.

Health conditions: Health conditions caused by hormone imbalances, such as hyperthyroidism (too much thyroid hormone), hyperparathyroidism (too much parathyroid hormone), and Cushing's syndrome (too much adrenal hormone) may increase the risk for osteoporosis because they interfere with the regulation of the hormones that regulate remodeling. Gastrointestinal disorders, such as celiac disease and Crohn's disease, which affect absorption of calcium and vitamin D also increase the risk. Early onset menopause brought on by the removal of the uterus (hysterectomy) and the complete removal of the ovaries (oophrectomy) is associated with osteoporosis.

For men, alcoholism is one of the leading risk factors for osteoporosis. Excess consumption of alcohol reduces bone formation and interferes with the body's ability to absorb calcium.

Individuals who experience serious depression have increased rates of bone loss. Depression activates the sympathetic nervous system, which responds to impending danger or stress, causing the release of a chemical compound called noradrenaline that harms bone-building cells.

Women and men with eating disorders, such as anorexia nervosa or bulimia, are at higher risk of lower bone density in their lower backs and hips. Eating disorders have significant physical consequences. Affected individuals can experience nutritional and hormonal problems that negatively impact bone density. Low body weight in females causes the body to stop producing estrogen, resulting in a condition known as amenorrhea, or absent menstrual periods. Low estrogen levels contribute to significant losses in bone density. In addition, individuals with anorexia often produce excessive amounts of the adrenal hormone cortisol, which is known to trigger bone loss. Other problems, such as a decrease in the production of growth hormone and other growth factors, low body weight, calcium deficiency, and malnutrition, all contribute to bone loss in individuals with eating disorders. Weight loss, restricted dietary intake, and testosterone deficiency may be responsible for the low bone density found in males with the disorder. Studies suggest that low bone mass (osteopenia) is common in people with anorexia and that it occurs early in the course of the disease. Girls with anorexia are less likely to reach their peak bone density and therefore may be at increased risk for osteoporosis and fracture throughout life.

Medications: Certain medications may decrease the body's ability to absorb calcium and may increase the risk of developing osteoporosis. Postmenopausal women who have had breast cancer are at increased risk of osteoporosis, especially if they were treated with medications such as anastrozole (Arimidex®), letrozole (Femara®), and exemestane (Aromasin®), which suppress estrogen. Women treated with tamoxifen (Nolvadex®) do not seem to develop an increase in bone loss.

Diuretics, or medications that prevent buildup of fluids in the body, can cause the kidneys to excrete more calcium, leading to thinning bones. Diuretics that cause calcium loss include furosemide (Lasix®), bumetanide (Bumex®), ethacrynic acid (Edecrin®), and torsemide (Demadex®).

Long-term use of the blood-thinning medication heparin, the drug methotrexate (Rheumatrex®), some anti-seizure medications such as phenytoin (Dilantin®), and aluminum-containing antacids such as Amphojel®, may also lead to bone loss.

Cholestyramine (Cholestin®), used to control blood cholesterol levels, may decrease calcium absorption and increase the risk of osteoporosis. Gonadotropin-releasing hormones (such as Lupron®) used for the treatment of endometriosis may also decrease calcium absorption and increase the risk of osteoporosis.

Corticosteroids, such as prednisone (Deltasone®), may lead to osteoporosis. Approximately 30-50% of individuals taking corticosteroids long-term develop osteoporosis. Relatively short courses (two to three months) of more than 7.5 milligrams of prednisone (Deltasone®) can cause significant bone loss. The common long-term use of corticosteroids in conditions, such as rheumatoid arthritis, results in a dramatic increase in vertebral and ultimately hip fracture rates.

Low calcium intake: A lifelong lack of calcium plays a major role in the development of osteoporosis. Low calcium intake contributes to poor bone density, early bone loss, and an increased risk of fractures.

Lack of exercise: Exercise can increase bone density at any age. Children who are physically active and consume adequate amounts of calcium-containing foods have the greatest bone density.

Excess soda consumption: The link between osteoporosis and caffeinated sodas is not clear, but caffeine and phosphoric acid in the drinks may interfere with calcium absorption. Caffeine is also a diuretic, which may increase mineral loss.