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TOPICS:

How Do Bones Change Over Time?
Why Do Bones Fracture?
How Is Osteoporosis Diagnosed?
Who Is At Greatest Risk?
How Does Nutrition Affect Bone Health?
How Do Hormones Affect Bone Health?
Can Medications Prevent Fractures?
Summary
References
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Osteoporosis: Can You Feel It In Your Bones?

Osteoporosis is a progressive disease of the skeletal system in which bones become so brittle that they break more easily than they should. According to the World Health Organization, this disease is characterized by a combination of two factors:

While this definition makes it clear that osteoporosis is not simply the consequence of low bone mass, there is no diagnostic test to assess bone’s structural quality. As such, osteoporosis is currently diagnosed and defined based on low bone mineral density (BMD) only.

There is no “cure” for osteoporosis, but there are measures you can take to prevent its onset or reverse its course—no matter what age you are—because bones continue to be renewed throughout life.

How Do Bones Change Over Time?

Although you can’t feel it happening, your bones are constantly undergoing a process called bone remodeling. Old and damaged bone tissue is continuously being cleared away (bone resorption) and replaced with healthy, new tissue (bone formation). As we age, our bodies become less efficient at constructing new bone, leading to a gradual but cumulative loss of bone strength.

Bone remodeling occurs in both the tough, outer core, which is high in minerals, and the spongy, inner core,
which is rich in marrow and blood vessels. Just as in home remodeling, quality materials (nutrients) and effective labor (cells involved in bone remodeling) produce the best results.

Exercise is also critical because it targets which bones are remodeled and how. Demands placed on certain bones trigger extra remodeling, so that limbs under repetitive stress, such as a pitcher’s throwing arm, become thicker and stronger over time. Weight-bearing exercise also engages muscles, which push and tug against bones, stimulating growth of new bone tissue.

Bones continue to grow more dense and thick until peak bone mass is reached, which for most people is typically sometime in their early twenties. However, what is “peak” bone mass for one person may be very different than that of another. There are significant differences in the average peak bone mass between the sexes, and across races, ethnic groups and even people living in different geographical areas within the same country.

In most healthy people, the rate of bone formation keeps up with bone resorption until their late thirties or early forties, at which time the balance
shifts and bone “demolition” begins to outpace “construction” of new bone. At first, this shift is subtle and results in minimal bone loss. For women, bone loss accelerates at menopause due to declining levels of estrogen and other hormones essential to bone health. Genetics, hormones, exercise, nutrition and other lifestyle factors all influence how dense our bones become and remain throughout life.

Why Do Bones Fracture?

Bone is living tissue with complex nutritional needs. New bone is formed by an interlocking matrix of the protein collagen, which is “cemented” into place by a mix of minerals. Calcium phosphate and calcium carbonate predominate in this mix, but it also includes magnesium and trace minerals, which are micronutrients found in extraordinarily small amounts in the body, yet are essential for many body functions including bone health.

Old or damaged bone is demolished (resorbed) by chemicals that dissolve the minerals and disrupt the collagen matrix. When the bone remodeling process favors demolition, bones become more porous (less dense). If the integrity of the protein collagen matrix is also compromised, bones become increasingly weak and brittle and are no longer capable of efficiently repairing the microscopic fractures that result from mild trauma.

Some bones are more fragile than others to begin with. The vertebrae, pelvis, hip, wrist, flat bones, and the ends of long bones are a more porous, honeycomb-like bone that is highly sensitive to metabolic changes. These bones are also the most susceptible to loss of density and structural integrity as we age.

The geometry of the wrist, hip and spine also makes them extremely susceptible to breakage. In the spine, vertebrae may collapse from the stress of the body’s own weight or from light lifting. Most wrist and hip fractures result from falls. In fact, the key risk factors for fracture revolve around an older person’s greater propensity to fall. Falls are often associated with the common effects of aging, including poor eyesight, reduced muscle strength and coordination, and/or mental confusion due to medications or dementia.

How Is Osteoporosis Diagnosed?

In most people, osteoporosis is a silent thief of the body’s structural support system. However, sometimes there are visible warning signs such as:

Without any of these visible warning signs, the only way to “see” the porous bone that is the hallmark of osteoporosis is to perform a biopsy, which is impractical. The most common method of testing for osteoporosis is Dual Energy X-ray Absorptiometry (DEXA or DXA), which measures BMD via x-rays, usually of the hip or spine. The “normal” reference value is the peak bone mass of a healthy, 20-year-old Caucasian woman. A BMD measurement significantly below this peak value results in a diagnosis of osteoporosis. Osteopenia, or being at risk for osteoporosis, is the diagnosis for those with scores slightly below “normal.” Unfortunately, these diagnostic criteria do not account for either the natural biological variation that occurs or for normal age-related bone loss. “This means that unless women maintain their bone mass at peak levels throughout their life span, they will be labeled as at risk or diseased,” points out Gillian Sanson, author of The Myth of Osteoporosis.

In addition, there are well-known issues with the accuracy of DXA machines because there are no international standards for their calibration. Using the same DXA machine for repeat tests is recommended to accurately detect changes in BMD over time. Despite these concerns, DXA measurement remains the leading diagnostic test for osteo-porosis; and most research, treatment and prevention efforts focus on increasing BMD.

Some practitioners prefer to screen for osteoporosis in lower-risk patients using lower radiation BMD methods, such as single photon absorptiometry (SPA) of the wrist, which has proven effective in predicting spinal bone density. Another option for low risk patients is measuring BMD in the heel using SPA or ultrasound.

For a more complete picture of bone health, some practitioners may also request a urine test that measures biochemical markers released during the bone remodeling process. Whereas it may take years to show changes in BMD, repeated urine testing over just a few months can help identify if there is an increase or decrease in bone breakdown. This provides more immediate feedback on whether or not lifestyle changes or treatments are working to improve bone health.

Does Low Bone Density Cause Fractures?

Having low BMD does not cause fractures, but it is one of many risk factors. A low BMD score has not been shown to accurately identify which women will fracture as they age. Many people who fracture do not have osteoporosis, and many people with osteoporosis never fracture. According to Sanson, the vast majority of the population will never fracture as a result of low bone density.

Who Is At Greatest Risk?

The chances of developing osteoporosis go up with every year of life, and some of the risk factors are beyond our control. For example, women are at greater risk than men because they typically have smaller, less dense bones. Caucasian women usually have greater bone loss than African American and Hispanic women. Yet, Asian women tend to have lower bone mass than Caucasian women, but suffer fewer osteoporotic fractures, which tells us it is not strictly a matter of bone mineral density. Genetics, diet, nutrition, hormone balance and other factors also play a role in bone health.

The following lifestyle choices, which are within our control, are associated with bone loss:

Although osteoporosis most often develops as a result of the aging process, in some cases it can be triggered by another illness or use of certain medications. In particular, the following treatments are associated with increased bone loss:

How Does Nutrition Affect Bone Health?

Calcium balance is so important that the human body has evolved several mechanisms to compensate for fluctuations in diet, intestinal absorption and excretion. For example, people with a low-calcium diet will have higher levels of calcitriol (a form of vitamin D) in their blood to improve calcium absorption.

However, contrary to popular belief, most Americans don’t have trouble getting enough calcium from their diets, but they do have trouble effectively absorbing calcium. Vitamin and mineral deficiencies, which are increasingly common as we age, inhibit our ability to make use of calcium to build bone. Nutrients known to affect bone health include:

Another major digestive factor that affects nutrition is stomach secretions, specifically hydrochloric acid, which is necessary for the breakdown of foods so nutrients can be absorbed. As we age, the cells in our stomach lining produce less hydrochloric acid, hampering the absorption of nutrients such as calcium and the other vitamins and minerals essential for bone health.

Most stomach problems stem from too little digestive acid, instead of too much. However, many people reach for over-the-counter antacids to treat stomach upset, not realizing that these antacids block the action of hydrochloric acid, further aggravating the source of the stomach pain, and contributing even more to osteoporosis by blocking calcium absorption.

Digestive disorders such as celiac disease and Crohn’s disease, as well as eating disorders like anorexia also interfere with nutrient absorption.

How Do Hormones Affect Bone Health?

Hormones are important players in bone remodeling throughout life, especially the sex hormones. Abrupt declines in sex hormones produce rapid bone loss in both men and women. For example, women who have a hysterectomy, especially younger women, are at very high risk of osteoporosis, while men with low testosterone, at any age, are far more likely to suffer fractures.

The estrogen hormones promote bone health primarily by inhibiting bone resorption. After menopause (and its accompanying decrease in estrogen levels), the bone turnover rate accelerates leading to more rapid bone loss, which is one reason estrogen therapy is so often recommended. However, estrogen coupled with progesterone provides added benefits for bone health because progesterone stimulates bone formation and contributes to bone strength, typically resulting in a significant net gain in bone.

Women who experience rapid bone loss are typically deficient in both estrogen and testosterone, which is believed to stimulate bone formation, increase calcium absorption, and increase bone’s ability to retain calcium. It is clear that the combined sex hormones play an important role in maintaining bone health.

DHEA (dehydroepiandrosterone) contributes to bone health in a variety of ways. It binds to estrogen receptors to block the resorption effects of estrogen; it increases progesterone levels, aiding bone formation; and it works with testosterone to stimulate bone formation and calcium absorption. It appears to be the only hormone that is capable of both inhibiting bone resorption and stimulating bone formation. It is also a precursor hormone that can be converted by the body into other hormones, including estrogen and testosterone. So, not only does it have direct effects on bone remodeling, but it also increases the levels of other major hormones that affect bone health.

Calcitonin and parathyroid hormone (PTH) are two hormones that work together to “manage” calcium levels. When calcium is ingested, some is absorbed into the bloodstream, and some is stored in bone. If blood calcium levels are low, PTH signals the bones to release calcium. This is in opposition to calcitonin, which acts to reduce calcium in the blood and is a potent inhibitor of bone resorption.

Thyroid hormone influences the bone remodeling process. Because thyroid hormone boosts the energy of all cells in the body, it speeds up both bone resorption and formation. Too little thyroid hormone stunts growth in children, while too much can weaken the skeleton because bone resorption occurs faster than formation.

Cortisol, produced in the adrenal gland, also has complex effects on bone and needs to be in balance. Small amounts are necessary for healthy bone development, but large amounts serve to block bone formation, leading to bone loss and a very high risk of fracture. Therefore, stress is detrimental to bone health, just as it is to other parts of the body, because it leads to an excess of cortisol.

Human growth hormone (HGH) is believed to promote bone health by boosting bone formation, although studies show mixed results. Proponents say growth hormone resorbs more bone in the first 12 to 18 months, and then acts to build bone, eventually raising bone mineral density over a longer period of time.

Even oxytocin, often referred to as the “cuddle hormone,” is believed to play a role in bone health, with recent research demonstrating a relationship between low oxytocin levels and severe osteoporosis.

Can Medications Prevent Fracture?

Osteoporosis medications may benefit those with a high risk of fracture, but concerns exist about their side effects and long-term safety. Individuals at different ages are likely to come to different conclusions about whether the benefits outweigh the risks.

The most common treatment for osteoporosis is currently a class of powerful, anti-resorptive drugs known as bisphosphonates, including Fosamax® and Actonel®, which bind calcium to bone tissue. While they do increase bone mineral density and appear to reduce the risk of vertebral, hip and other fractures in the short term (five or fewer years), they may have long-term effects that may not be reversible. For this reason, Sanson argues that the risk of treatment for younger women is likely to dwarf the benefits.

Bone biopsies of women who suffered fragility fractures while on Fosamax® show that bone formation is nearly 100 times slower. By suppressing bone turnover, bisphosphonates seem to reduce the bone’s ability to bend under pressure without breaking. In other words, bisphosphonates may not build bone so much as harden it. If the high risk of fracture justifies this treatment, exercise can boost effectiveness by promoting bone renewal.

Recently, bisphosphonates have been linked to a few negative outcomes, including:

Alternatives to bisphosphonates have shown limited effectiveness in preventing fractures, or lack reliable proof of safety.

Summary

It’s never too late—or too early—to work on optimizing bone health. Preventing osteoporosis and bone fracture requires paying attention to multiple facets of bone health including:

References

Connections is a publication of Women's International Pharmacy, which is dedicated to the education and management of PMS, menopause, infertility, postpartum depression, and other hormone-related conditions and therapies.

This publication is distributed with the understanding that it does not constitute medical advice for individual problems. Although material is intended to be accurate, proper medical advice should be sought from a competent healthcare professional.

Publisher: Constance Kindschi Hegerfeld, Executive VP, Women's International Pharmacy
Co-Editors: Julie Johnson and Carol Petersen, RPh, CNP; Women's International Pharmacy
Writer: Kathleen McCormick, McCormick Communications Illustrator: Amelia Janes, Midwest Educational Graphics

Copyright © May 2013, Women's International Pharmacy. This newsletter may be printed from the PDF version and photocopied for educational purposes, provided that your copy(s) include full copyright and contact information.
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