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Of course, not everyone develops osteoporosis. We've all known people who've made it into their 80s or 90s without fractures or a noticeable loss of height — two telltale symptoms of the condition.

Certain characteristics make some people more likely to develop the disease. To begin with, being female is a major risk factor: About 80% of the 10 million Americans with osteoporosis are women. Beyond that, some risk factors are common to both men and women, while others vary by sex.

Figure 4: A look at osteoporotic bone Non-osteoporotic bone A look at osteoporotic bone The photograph at left shows a microscopic view of bone from a 75-year-old woman who does not suffer from osteoporosis. You'll notice that her bone is denser than the bone shown at right, which is from a 47-year-old woman with osteoporosis who has had several spinal fractures.

Osteoporosis risk in women

In the National Institutes of Health's Study of Osteoporotic Fractures — a landmark observational study of almost 10,000 women ages 65 and older — researchers looked at characteristics that are significantly more common among women who have osteoporosis than among those who don't. The results of this and other osteoporosis studies give us a pretty good idea of the factors that can predispose certain women to osteoporosis.

No one has yet devised a simple formula for calculating individual risk for osteoporosis. At this point, the best initial way to assess your risk is to scan the following list and try to determine how many of the factors apply to you. It's also worthwhile to discuss the matter with your doctor. Together, you can determine whether you should have a bone density evaluation.

The following factors influence a woman's chances of developing osteoporosis:

Age. Time alone increases the risk for osteoporosis. The researchers in the Study of Osteoporotic Fractures noted that, on average, bone mass fell by approximately 5% every five years after age 65. The risk for a fracture also increases with age. For example, among white women under age 35 there are just two hip fractures per 100,000, but that number soars to 3,000 hip fractures per 100,000 at age 85 or older.

Sex. Women are more likely than men to develop osteoporosis because women have smaller skeletons, their bone loss begins earlier, and menopause brings on a period of rapid bone loss.

Body type. Small-boned, thin women tend to have lower bone density.

Personal and family history. Genes may go a long way toward determining susceptibility to osteoporosis. Adults who have broken a bone or whose first-degree family members have had fractures are at greater risk. Women whose mothers had fractures after age 50 have significantly lower bone density than those whose mothers did not break bones.

Ethnicity. Caucasian and Asian women are more likely to develop osteoporosis.

Estrogen levels. Since estrogen retards bone resorption, women who are past menopause or those who have had their ovaries removed are at higher risk. So are younger women who have too little body fat (sometimes because of excessive exercise, anorexia, or bulimia) and consequently too little estrogen to menstruate regularly.

Low calcium levels. Lack of calcium in your diet — as well as conditions that may interfere with calcium absorption by the intestines — results in lower calcium levels in the blood. The body compensates by releasing calcium from the bones, weakening them.

Inactivity. When bones are at rest, formation slows.

Smoking. Smokers tend to lose bone faster than nonsmokers. Smoking may both interfere with the absorption of calcium and lower the amount of estrogen produced by the body. A 2004 analysis of several studies found that men and women who smoked were at greater risk of breaking a hip or other bone. In fact, the Surgeon General's report on osteoporosis noted that smokers are 55% more likely than nonsmokers to break a hip.

Excessive use of alcohol. Heavy alcohol use can reduce bone mass. Experts believe that alcohol may interfere with the body's ability to convert inactive vitamin D into its active form. It also appears to hamper bone formation and increase losses of calcium and magnesium from the body. While it's clear that heavy drinking has a negative effect on bones, some studies have found that moderate drinking is associated with increased bone mass. The Nurses' Health Study found that women who had one drink a day had greater bone mass in the spine than women who didn't drink at all. Still, alcohol may be more harmful than helpful. That's because alcohol interferes with balance and makes falling more likely. That same study revealed that women who had one drink a day were twice as likely as nondrinkers to break a hip.

Medications. People who take certain drugs — such as glucocorticoids, antiseizure medications, cyclosporine A (which is used in organ transplants), and excessive thyroid hormones — may be at greater risk for osteoporosis, as these drugs often contribute to bone loss.

Medical conditions. Congenital disorders that affect bone mass over a lifetime, such as Marfan's syndrome, Ehlers-Danlos syndrome, or osteogenesis imperfecta, increase the risk for osteoporosis. Some chronic conditions, including anorexia, certain cancers, liver disease, and disorders that affect absorption of minerals, may also have an impact (see "Possible causes of secondary osteoporosis").

One disorder that increases the risk for osteoporosis is primary hyperparathyroidism. People with this disorder have abnormally high levels of parathyroid hormone (PTH), which helps regulate the amount of calcium in the blood. The excessive levels of PTH spur the removal of calcium from bones and increase the amount of calcium in the blood. In turn, the kidneys often try to compensate for the extraordinarily high levels of calcium in the blood by excreting large amounts of it in the urine. Every year, approximately 100,000 new cases are detected, with most occurring among women. Often, this condition has no symptoms and is found only when a routine blood test shows high calcium levels. However, as it advances, it can cause kidney stones, muscle weakness, fatigue, and eventually osteoporosis.

Fracture risk Fracture risk for women For women 50% risk: 1 out of 2 women will have an osteoporosis-related fracture in her lifetime. Fracture risk for men For men 25% risk: 1 out of 4 men will have an osteoporosis-related fracture in his lifetime.

Osteoporosis risk in men

Two factors make men less vulnerable than women to bone loss: They have a greater bone density at maturity, and they experience a more gradual decline in hormone levels. Nevertheless, two million men in the United States have the disease.

Men aren't immune Osteoporosis is often thought of as a women's disease. While osteoporosis does affect more women than men, many people don't realize that a significant number of men — about two million in the United States alone — have this condition. In fact, a 50-year-old man has a 13% chance of breaking his hip, spine, or wrist at some point in the future. The 2004 Surgeon General's report on bone health and osteoporosis warned that the notion that only women get osteoporosis can lead to delays in identifying and treating the disease in men. One of the goals of the Surgeon General's report is to increase awareness among the public and health professionals that osteoporosis affects men as well as women. Men aren't immune About 20% of Americans with osteoporosis are men.

When men under age 75 develop osteoporosis, it's often because of an underlying condition and is considered secondary, rather than primary, osteoporosis. Many of the most common causes of secondary osteoporosis in men can also cause osteoporosis in women. In these cases, treatments address the condition or conditions that are responsible. For example, testosterone replacement therapy, administered through injections or a patch, can boost low testosterone levels in men and help retard bone loss.

The risk factors for osteoporosis that are particularly relevant to men include the following:

Medications. Glucocorticoid usage is one of the most common causes of secondary osteoporosis. This class of medications is used to treat asthma, arthritis, and other diseases. Anticonvulsants, some drugs given to organ transplant patients, and certain cancer drugs also increase risk.

Low sex hormones. In men, testosterone levels may fall with age.

Heavy alcohol use. As is the case with women, heavy drinking can damage bone health by reducing bone mass. In addition, alcohol interferes with balance, making falls more likely.

Gastrectomy. This operation — in which part or all of the stomach is removed — can reduce the amount of calcium the body absorbs.

Medical conditions. See "Possible causes of secondary osteoporosis."

Other factors. As with women, the following factors place men at greater risk of developing osteoporosis: heredity, aging, inactivity, smoking, low calcium levels, and ethnicity (Caucasian men are most in jeopardy of developing osteoporosis).

Source: from Harvard Health Publications, Copyright © 2008 Harvard University. All rights reserved. Harvard Medical School does not endorse products.
Used with permission of StayWell.
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