Osteoporosis Sourcebook, 2nd Ed.

By Omnigraphics

Provides information about the risk factors of osteoporosis along with answers to questions about calcium intake and supplements and other dietary needs, hormone replacement therapies, the drugs used to treat osteoporosis, and surgical options.

• Language: English
• Publisher: Omnigraphics
• Release date: Mar 1, 2019
• ISBN: 9780780816862

Book preview

Preface

About This Book

Many people think of bones as simple, solid structures that make up the skeletal system. In truth, bones are complex, living tissues that go through a constant process of building up and tearing down. This process, called bone remodeling, rebuilds the bones as people grow and age. One of the main components of bone is calcium. In fact, the skeletal system contains 99 percent of the body’s calcium. In osteoporosis, which literally means porous bones, excessive bone loss results in a depletion of calcium. The gradual weakening of the bones over time makes them more susceptible to fractures and can lead to disfigurement and pain. Most people reach a peak bone mass between the ages of 25 and 35. By age 40, bone loss usually reaches 0.5 percent per year. Postmenopausal women can lose 2 to 3 percent per year and can have lost 50 percent of their bone mass by age 70 or 80. In osteoporosis, bone loss accelerates. Since the loss occurs over time, the effect may not be noticed until substantial bone loss has occurred, often signaled by an unexpected fracture. Osteoporosis cannot be detected by X-ray until the bone loss has reached 30 to 50 percent of bone mass, by which time the calcium depletion cannot be reversed. Because of this, prevention and early diagnosis are critical.

Osteoporosis Sourcebook, Second Edition provides information so that the layperson can identify the important risk factors of osteoporosis and the life-style changes needed to offset them. It provides answers to questions about calcium intake and supplements and other dietary needs, the drugs used to treat osteoporosis, and surgical options. It also suggests coping strategies for those suffering from the disease. The book concludes with a glossary of related terms and a directory of resources.

How to Use This Book

This book is divided into parts and chapters. Parts focus on broad areas of interest. Chapters are devoted to single topics within a part.

Part I: Osteoporosis: An Overview begins with an introduction to osteoporosis and gives a brief insight into the risk factors and preventive measures of the disease. It talks about the basic structure and functions of the bone and highlights the factors that influence/affect the bone health. It also distinguishes osteoporosis from arthritis and emphasizes the importance of proper diagnosis.

Part II: Osteoporosis in Women, Children, Men, and Older Adults outlines the impact of osteoporosis and its costs, both monetary and in terms of health effects, for various segments of population such as women, children, men, and older adults.

Part III: Osteoporosis and Related Conditions provides information about diseases and conditions that lead to or aggravate osteoporosis or that have symptoms similar to those produced by osteoporosis. The conditions include dripping candle wax bone disease, fibrous dysplasia, Gaucher disease, otosclerosis, hypercalcemia, hypocalcemia, hyperparathyroidism, hypophosphatasia, inflammatory bowel disease, multiple myeloma, oral health, osteopetrosis, osteogenesis imperfecta, and Paget Disease.

Part IV: Risk Factors and Prevention of Osteoporosis discusses in detail about the factors that lead to osteoporosis and suggests healthy lifestyle choices to minimize those factors.

Part V: Diagnosis and Treatment of Osteoporosis traces the process of diagnosing osteoporosis as early as possible and treating the condition effectively. It reviews the various options in drug and surgical therapies and points out their drawbacks and limitations. It also highlights some of the complementary and alternative medicines available for osteoporosis.

Part VI: Living with Osteoporosis deals with the impact to osteoporosis on an individual. It explains how lifestyle changes can help patients with osteoporosis lead a healthy life. The part also deals with the strategies to cope up with the chronic pain caused by the disease.

Part VII: Additional Help and Information provides a glossary of osteoporosis-related terminology and a list of resources for patients with osteoporosis or related conditions.

Bibliographic Note

This volume contains documents and excerpts from publications issued by the following U.S. government agencies: Agricultural Research Service (ARS); Centers for Disease Control and Prevention (CDC); Centers for Medicare & Medicaid Services (CMS); Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD); Genetic and Rare Diseases Information Center (GARD); Genetics Home Reference (GHR); Go4Life; National Cancer Institute (NCI); National Center for Biotechnology Information (NCBI); National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS); National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK); National Institute of Mental Health (NIMH); National Institute of Neurological Disorders and Stroke (NINDS); National Institute on Aging (NIA); National Institute on Alcohol Abuse and Alcoholism (NIAAA); National Institute on Deafness and Other Communication Disorders (NIDCD); National Institutes of Health (NIH); NIH News in Health; NIH Osteoporosis and Related Bone Diseases—National Resource Center (NIH ORBD—NRC); Office of Dietary Supplements (ODS); Office of Disease Prevention and Health Promotion (ODPHP); Office on Women’s Health (OWH); U.S. Department of Energy (DOE); U.S. Department of Veterans Affairs (VA); and U.S. Food and Drug Administration (FDA).

It may also contain original material produced by Omnigraphics and reviewed by medical consultants

About the Health Reference Series

The Health Reference Series is designed to provide basic medical information for patients, families, caregivers, and the general public. Each volume takes a particular topic and provides comprehensive coverage. This is especially important for people who may be dealing with a newly diagnosed disease or a chronic disorder in themselves or in a family member. People looking for preventive guidance, information about disease warning signs, medical statistics, and risk factors for health problems will also find answers to their questions in the Health Reference Series. The Series, however, is not intended to serve as a tool for diagnosing illness, in prescribing treatments, or as a substitute for the physician/patient relationship. All people concerned about medical symptoms or the possibility of disease are encouraged to seek professional care from an appropriate healthcare provider.

A Note about Spelling and Style

Health Reference Series editors use Stedman’s Medical Dictionary as an authority for questions related to the spelling of medical terms and the Chicago Manual of Style for questions related to grammatical structures, punctuation, and other editorial concerns. Consistent adherence is not always possible, however, because the individual volumes within the Series include many documents from a wide variety of different producers, and the editor’s primary goal is to present material from each source as accurately as is possible. This sometimes means that information in different chapters or sections may follow other guidelines and alternate spelling authorities. For example, occasionally a copyright holder may require that eponymous terms be shown in possessive forms (Crohn’s disease vs. Crohn disease) or that British spelling norms be retained (leukaemia vs. leukemia).

Medical Review

Omnigraphics contracts with a team of qualified, senior medical professionals who serve as medical consultants for the Health Reference Series. As necessary, medical consultants review reprinted and originally written material for currency and accuracy. Citations including the phrase Reviewed (month, year) indicate material reviewed by this team. Medical consultation services are provided to the Health Reference Series editors by:

Dr. Vijayalakshmi, MBBS, DGO, MD

Dr. Senthil Selvan, MBBS, DCH, MD

Dr. K. Sivanandham, MBBS, DCH, MS (Research), PhD

Our Advisory Board

We would like to thank the following board members for providing initial guidance on the development of this series:

Dr. Lynda Baker, Associate Professor of Library and Information Science, Wayne State University, Detroit, MI

Nancy Bulgarelli, William Beaumont Hospital Library, Royal Oak, MI

Karen Imarisio, Bloomfield Township Public Library, Bloomfield Township, MI

Karen Morgan, Mardigian Library, University of ­ Michigan-Dearborn, Dearborn, MI

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Health Reference Series Update Policy

The inaugural book in the Health Reference Series was the first edition of Cancer Sourcebook published in 1989. Since then, the Series has been enthusiastically received by librarians and in the medical community. In order to maintain the standard of providing high-quality health information for the layperson the editorial staff at Omnigraphics felt it was necessary to implement a policy of updating volumes when warranted.

Medical researchers have been making tremendous strides, and it is the purpose of the Health Reference Series to stay current with the most recent advances. Each decision to update a volume is made on an individual basis. Some of the considerations include how much new information is available and the feedback we receive from people who use the books. If there is a topic you would like to see added to the update list, or an area of medical concern you feel has not been adequately addressed, please write to:

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Part One

Osteoporosis: An Overview

Chapter 1

Introduction to Osteoporosis

Chapter Contents

Section 1.1—The Skeletal System and Bones

Section 1.2—What Is Osteoporosis?

Section 1.3—Osteoporosis Risk Factors and Prevention

Section 1.4—Types of Osteoporosis

Section 1.1

The Skeletal System and Bones

This section includes text excerpted from Introduction to the Skeletal System, National Cancer Institute (NCI), July 1, 2002. Reviewed January 2019.

Humans are vertebrates, animals having a vertebral column or backbone. We rely on a sturdy internal frame that is centered on a prominent spine. The human skeletal system consists of bones, cartilage, ligaments, and tendons and accounts for about 20 percent of our body weight.

The living bones in our bodies use oxygen and give off waste products in metabolism. They contain active tissues that consume nutrients, require a blood supply and change shape or remodel in response to variations in mechanical stress.

Bones provide a rigid framework, known as the skeleton, that support and protect the soft organs of the body.

The skeleton supports the body against the pull of gravity. The large bones of the lower limbs support the trunk when standing.

The skeleton also protects the soft body parts. The fused bones of the cranium surround the brain to make it less vulnerable to injury. Vertebrae surround and protect the spinal cord and bones of the rib cage help protect the heart and lungs of the thorax.

Bones work together with muscles as simple mechanical lever systems to produce body movement.

Bones contain more calcium than any other organ. The intercellular matrix of bone contains large amounts of calcium salts, the most important being calcium phosphate.

When blood calcium levels decrease below normal, calcium is released from the bones so that there will be an adequate supply for metabolic needs. When blood calcium levels are increased, the excess calcium is stored in the bone matrix. The dynamic process of releasing and storing calcium goes on almost continuously.

Hematopoiesis, the formation of blood cells, mostly takes place in the red marrow of the bones.

In infants, red marrow is found in the bone cavities. With age, it is largely replaced by yellow marrow for fat storage. In adults, red marrow is limited to the spongy bone in the skull, ribs, sternum, clavicles, vertebrae, and pelvis. Red marrow functions in the formation of red blood cells, white blood cells, and blood platelets.

Structure of Bone Tissue

There are two types of bone tissue: compact and spongy. The names imply that the two types differ in density, or how tightly the tissue is packed together. There are three types of cells that contribute to bone homeostasis. Osteoblasts are bone-forming cell, osteoclasts resorb or break down bone, and osteocytes are mature bone cells. An equilibrium between osteoblasts and osteoclasts maintains bone tissue.

Compact Bone

Compact bone consists of closely packed osteons or haversian systems. The osteon consists of a central canal called the osteonic (haversian) canal, which is surrounded by concentric rings (lamellae) of matrix. Between the rings of matrix, the bone cells (osteocytes) are located in spaces called lacunae. Small channels (canaliculi) radiate from the lacunae to the osteonic (haversian) canal to provide passageways through the hard matrix. In compact bone, the haversian systems are packed tightly together to form what appears to be a solid mass. The osteonic canals contain blood vessels that are parallel to the long axis of the bone. These blood vessels interconnect, by way of perforating canals, with vessels on the surface of the bone.

Figure 1.1. Compact Bone and Spongy (Cancellous Bone)

Spongy (Cancellous) Bone

Spongy (cancellous) bone is lighter and less dense than compact bone. Spongy bone consists of plates (trabeculae) and bars of bone adjacent to small, irregular cavities that contain red bone marrow. The canaliculi connect to the adjacent cavities, instead of a central haversian canal, to receive their blood supply. It may appear that the trabeculae are arranged in a haphazard manner, but they are organized to provide maximum strength similar to braces that are used to support a building. The trabeculae of spongy bone follow the lines of stress and can realign if the direction of stress changes.

Bone Development and Growth

The terms osteogenesis and ossification are often used synonymously to indicate the process of bone formation. Parts of the skeleton form during the first few weeks after conception. By the end of the eighth week after conception, the skeletal pattern is formed in cartilage and connective tissue membranes and ossification begins.

Bone development continues throughout adulthood. Even after adult stature is attained, bone development continues for repair of fractures and for remodeling to meet changing lifestyles. Osteoblasts, osteocytes, and osteoclasts are the three cell types involved in the development, growth and remodeling of bones. Osteoblasts are bone-forming cells, osteocytes are mature bone cells and osteoclasts break down and reabsorb bone.

There are two types of ossification: intramembranous and endochondral.

Intramembranous

Intramembranous ossification involves the replacement of sheet-like connective tissue membranes with bony tissue. Bones formed in this manner are called intramembranous bones. They include certain flat bones of the skull and some of the irregular bones. The future bones are first formed as connective tissue membranes. Osteoblasts migrate to the membranes and deposit bony matrix around themselves. When the osteoblasts are surrounded by matrix they are called osteocytes.

Endochondral Ossification

Endochondral ossification involves the replacement of hyaline cartilage with bony tissue. Most of the bones of the skeleton are formed in this manner. These bones are called endochondral bones. In this process, the future bones are first formed as hyaline cartilage models. During the third month after conception, the perichondrium that surrounds the hyaline cartilage models becomes infiltrated with blood vessels and osteoblasts and changes into a periosteum. The osteoblasts form a collar of compact bone around the diaphysis. At the same time, the cartilage in the center of the diaphysis begins to disintegrate. Osteoblasts penetrate the disintegrating cartilage and replace it with spongy bone. This forms a primary ossification center. Ossification continues from this center toward the ends of the bones. After spongy bone is formed in the diaphysis, osteoclasts break down the newly formed bone to open up the medullary cavity.

The cartilage in the epiphyses continues to grow so the developing bone increases in length. Later, usually after birth, secondary ossification centers form in the epiphyses. Ossification in the epiphyses is similar to that in the diaphysis except that the spongy bone is retained instead of being broken down to form a medullary cavity. When secondary ossification is complete, the hyaline cartilage is totally replaced by bone except in two areas. A region of hyaline cartilage remains over the surface of the epiphysis as the articular cartilage and another area of cartilage remains between the epiphysis and diaphysis. This is the epiphyseal plate or growth region.

Bone Growth

Bones grow in length at the epiphyseal plate by a process that is similar to endochondral ossification. The cartilage in the region of the epiphyseal plate next to the epiphysis continues to grow by mitosis. The chondrocytes, in the region next to the diaphysis, age and degenerate. Osteoblasts move in and ossify the matrix to form bone. This process continues throughout childhood and the adolescent years until the cartilage growth slows and finally stops. When cartilage growth ceases, usually in the early twenties, the epiphyseal plate completely ossifies so that only a thin epiphyseal line remains and the bones can no longer grow in length. Bone growth is under the influence of growth hormone from the anterior pituitary gland and sex hormones from the ovaries and testes.

Even though bones stop growing in length in early adulthood, they can continue to increase in thickness or diameter throughout life in response to stress from increased muscle activity or to weight. The increase in diameter is called appositional growth. Osteoblasts in the periosteum form compact bone around the external bone surface. At the same time, osteoclasts in the endosteum break down bone on the internal bone surface, around the medullary cavity. These two processes together increase the diameter of the bone and, at the same time, keep the bone from becoming excessively heavy and bulky.

Figure 1.2. Bone Growth

Section 1.2

What Is Osteoporosis?

This section includes text excerpted from Osteoporosis, National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), February 28, 2016.

Osteoporosis is a disease in which your bones become weak and are more likely to break. If you have osteoporosis you are more likely to break bones in your hip, spine, and wrist.

Our bones are alive. Every day, our body breaks down old bone and puts new bone in its place. As we get older, our bones break down more bone than they put back. It is normal to lose some bone as we age. But, if we do not take steps to keep our bones healthy, we can lose too much bone and get osteoporosis.

Who Gets Osteoporosis

In the United States, millions of people either already have osteoporosis or are at high risk due to low bone mass. Osteoporosis can occur in both men and women and at any age, but it is most common in older women. Because more women get osteoporosis than men, many men think they are not at risk for the disease. However, it is a real risk for older men and women from all backgrounds.

Also, people from certain ethnic backgrounds may be more likely to have other health problems that increase their risk for bone loss. In addition, some diseases and medications can increase the risk of osteoporosis.

What Are the Symptoms of Osteoporosis?

Osteoporosis is called the silent disease because bone loss does not have any symptoms until a bone breaks.

Section 1.3

Osteoporosis Risk Factors and Prevention

This section includes text excerpted from Osteoporosis, National Institute on Aging (NIA), National Institutes of Health (NIH), June 26, 2017.

Although osteoporosis can strike at any age, it is most common among older people, especially older women. Men also have this disease. White and Asian women are most likely to have osteoporosis. Other women at great risk include those who:

Have a family history of broken bones or osteoporosis

Have broken a bone after age 50

Had surgery to remove their ovaries before their periods stopped

Had early menopause

Have not gotten enough calcium and/or vitamin D throughout their lives

Had extended bed rest or were physically inactive

Smoke (smokers may absorb less calcium from their diets)

Take certain medications, including medicines for arthritis and asthma and some cancer drugs

Used certain medicines for a long time

Have a small body frame

The risk of osteoporosis grows as you get older. At the time of menopause, women may lose bone quickly for several years. After that, the loss slows down but continues. In men, the loss of bone mass is slower. But, by age 65 or 70, men and women are losing bone at the same rate.

What Is Osteopenia?

Whether your doctor calls it osteopenia or low bone mass, consider it a warning. Bone loss has started, but you can still take action to keep your bones strong and maybe prevent osteoporosis later in life. That way you will be less likely to break a wrist, hip, or vertebrae (bone in your spine) when you are older.

Can My Bones Be Tested?

For some people, the first sign of osteoporosis is to realize they are getting shorter or to break a bone easily. Don’t wait until that happens to see if you have osteoporosis. You can have a bone density test to find out how strong your bones are.

The U.S. Preventive Service Task Force (USPSTF) recommends that women aged 65 and older be screened (tested) for osteoporosis, as well as women under age 65 who are at increased risk for an osteoporosis-related fracture.

A bone mineral density test compares your bone density to the bones of an average healthy young adult. The test result, known as a T-score, tells you how strong your bones are, whether you have osteoporosis or osteopenia, and your risk for having a fracture.

How Can I Keep My Bones Strong? Preventing Osteoporosis

There are things you should do at any age to prevent weakened bones. Eating foods that are rich in calcium and vitamin D is important. So is regular weight-bearing exercise, such as weight training, walking, hiking, jogging, climbing stairs, tennis, and dancing.

If you have osteoporosis, avoid activities that involve twisting your spine or bending forward from the waist, such as conventional sit-ups, toe touches, or swinging a golf club. Learn how to exercise safety with Go4Life (go4life.nia.nih.gov), the exercise and physical activity campaign from the National Institute on Aging (NIA).

Those are the best ways to keep your bones strong and healthy.

What Can I Do for My Osteoporosis?

Treating osteoporosis means stopping the bone loss and rebuilding bone to prevent breaks. Healthy lifestyle choices such as proper diet, exercise, and medications can help prevent further bone loss and reduce the risk of fractures.

But, lifestyle changes may not be enough if you have lost a lot of bone density. There are also several medicines to think about. Some will slow your bone loss, and others can help rebuild bone. Talk with your doctor to see if medicines might work to treat your osteoporosis.

In addition, you’ll want to learn how to fall-proof your home and change your lifestyle to avoid fracturing fragile bones.

Can I Avoid Falling?

When your bones are weak, a simple fall can cause a broken bone. This can mean a trip to the hospital and maybe surgery. It might also mean being laid up for a long time, especially in the case of a hip fracture. So, it is important to prevent falls.

Do Men Have Osteoporosis?

Osteoporosis is not just a woman’s disease. Not as many men have it as women do, maybe because most men start with more bone density. As they age, men lose bone density more slowly than women. But, men need to be aware of osteoporosis.

Experts don’t know as much about this disease in men as they do in women. However, many of the things that put men at risk are the same as those for women, including family history, not enough calcium or vitamin D, and too little exercise. Low levels of testosterone, too much alcohol, taking certain drugs, and smoking are other risk factors.

Older men who break a bone easily or are at risk for osteoporosis should talk with their doctors about testing and treatment.

Section 1.4

Types of Osteoporosis

This section includes text excerpted from Bone Health and Osteoporosis: A Report of the Surgeon General, National Center for Biotechnology Information (NCBI), 2004. Reviewed January 2019.

Primary Osteoporosis

Primary osteoporosis is mainly a disease of the elderly, the result of the cumulative impact of bone loss and deterioration of bone structure that occurs as people age. This form of osteoporosis is sometimes referred to as age-related osteoporosis. Since postmenopausal women are at greater risk, the term postmenopausal osteoporosis is also used. Younger individuals (including children and young adults) rarely get primary osteoporosis, although it can occur on occasion. This rare form of the disease is sometimes referred to as idiopathic osteoporosis, since in many cases the exact causes of the disease are not known, or idiopathic. Since the exact mechanisms by which aging produces bone loss are not all understood (that is, it is not always clear why some postmenopausal women develop osteoporosis while others do not), age-related osteoporosis is also partially idiopathic.

Idiopathic Primary Osteoporosis

There are several different forms of idiopathic osteoporosis that can affect both children and adolescents, although these conditions are quite rare. Juvenile osteoporosis affects previously healthy children between the ages of 8 and 14. Over a period of several years, bone growth is impaired. The condition may be relatively mild, causing only one or two collapsed bones in the spine (vertebrae), or it may be severe, affecting virtually the entire spine. The disease almost always goes into remission (spontaneously) around the time of puberty with a resumption of normal bone growth at that time. Patients with mild or moderate forms of the disease may be left with a curvature of the spine (kyphosis) and short stature, but those with a more severe form of the disease may be incapacitated for life.

Primary osteoporosis is quite rare in young adults. In this age-group, the disease is usually caused by some other condition or factor, such as anorexia nervosa or glucocorticoid use. When idiopathic forms of primary osteoporosis do occur in young adults, they appear in men as often as they do in women (this is in contrast to age-related primary osteoporosis, which occurs more often in women). The characteristics of the disease can vary broadly and may involve more than one disorder. Some young adults with idiopathic primary osteoporosis may have a primary defect in the regulation of bone cell function, resulting in depressed bone formation, increased bone resorption, or both. Others with a mild form of the disease may simply have failed to achieve an adequate amount of skeletal mass during growth. In some patients, the disease runs a mild course, even without treatment, and the clinical manifestations are limited to asymptomatic spinal compression fractures. More typically, however, multiple spine fractures occur over a five-to-ten-year period leading to a height loss of up to six inches.

Age-Related Osteoporosis

Age-related osteoporosis is by far the most common form of the disease. There are many different causes of the ailment, but the bone loss that leads to the disease typically begins relatively early in life, at a time when corrective action (such as changes in diet and physical activity) could potentially slow down its course. While it occurs in both sexes, the disease is two to three times more common in women. This is partly due to the fact that women have two phases of age-related bone loss—a rapid phase that begins at menopause and lasts four to eight years, followed by a slower continuous phase that lasts throughout the rest of life. By contrast, men go through only the slow, continuous phase. As a result, women typically lose more bone than do men. The rapid phase of bone loss alone in women results in losses of 5 to 10 percent of cortical bone (which makes up the hard outer shell of the skeleton) and 20 to 30 percent of trabecular bone (which fills the ends of the limb bones and the vertebral bodies in the spine, the sites of most osteoporotic fractures). The slow phase of bone loss results in losses of 20 to 25 percent of cortical and trabecular bone in both men and women, but over a longer period of time.

Although other factors such as genetics and nutrition contribute, both the rapid phase of bone loss in postmenopausal women and the slow phase of bone loss in aging women and men appear to be largely the result of estrogen deficiency. (This is demonstrated by the fact that correction of estrogen deficiency can prevent these changes.) For women, the rapid phase of bone loss is initiated by a dramatic decline in estrogen production by the ovaries at menopause. The loss of estrogen action on estrogen receptors in bone results in large increases in bone resorption, combined with reduced bone formation. The end result is thinning of the cortical outer shell of bone and damage to the trabecular bone structure. There may be some countervailing forces on this process, as the outside diameter of the bone can increase with age, thus helping to maintain bone strength.

By contrast, the slower phase of bone loss is thought to be caused by a combination of factors including age-related impairment of bone formation, decreased calcium and vitamin D intake, decreased physical activity, and the loss of estrogen positive effects on calcium balance in the intestine and kidney as well as its effects on bone. This leads to further impairment of absorption of calcium by the intestine and reduced ability of the kidney to conserve calcium. If the amount of calcium absorbed from the diet is insufficient to make up for the obligatory calcium losses in the stool and urine, serum calcium begins to fall. Parathyroid hormone (PTH) levels will then increase, removing calcium from bone to make up for the loss. The net result of this process is an increase in bone resorption. It is important to realize that these mineral losses need not be great to result in osteoporosis. A negative balance of only 50 to 100 mg of calcium per day (far less than the 300 mg of calcium in a single glass of milk) over a long period of time is sufficient to produce the disease.

For aging men, sex steroid deficiency also appears to be a major factor in age-related osteoporosis. Although testosterone is the major sex steroid in men, some of it is converted by the aromatase enzyme into estrogen. In men, however, the deficiency is mainly due to an increase in sex hormone binding globulin, a substance that holds both testosterone and estrogen in a form that is not available for use by the body. Between 30 to 50 percent of elderly men are deficient in biologically active sex steroids. In fact, except for the lack of the early postmenopausal phase, the process of bone loss in older men is similar to that for older women. As with women, the loss of sex steroid activity in men has an effect on calcium absorption and conservation, leading to progressive secondary increases in parathyroid hormone levels. As in older women, the resulting imbalance between bone resorption and formation results in slow bone loss that continues over life. Since testosterone may stimulate bone formation more than estrogen does, however, decreased bone formation plays a relatively greater role in the bone loss experienced by elderly men.

Secondary Osteoporosis

Young adults and even older individuals who get osteoporosis often do so as a byproduct of another condition or medication use. In fact, there are a wide variety of diseases along with certain medications and toxic agents that can cause or contribute to the development of osteoporosis. Individuals who get the disease due to these outside causes are said to have secondary osteoporosis. They typically experience greater levels of bone loss than would be expected for a normal individual of the same age, gender, and race. Secondary causes of the disease are common in many premenopausal women and men with osteoporosis; in fact, by some estimates the majority of men with osteoporosis exhibit secondary causes of the disease. In addition, up to a third of postmenopausal women with osteoporosis also have other conditions that may contribute to their bone loss.

Chapter 2

Bone Basics

Chapter Contents

Section 2.1—What Is Bone?

Section 2.2—Why Do We Have Bones?

Section 2.3—Bone Health for Life

Section 2.4—Boning Up

Section 2.1

What Is Bone?

This section includes text excerpted from What Is Bone? NIH Osteoporosis and Related Bone Diseases—National Resource Center (NIH ORBD—NRC), May 1, 2015. Reviewed January 2019.

To understand osteoporosis, it is important to learn about bone. Made mostly of collagen, bone is living, growing tissue. Collagen is a protein that provides a soft framework, and calcium phosphate is a mineral that adds strength and hardens the framework. This combination of collagen and calcium makes bone strong and flexible enough to withstand stress. More than 99 percent of the body’s calcium is contained in the bones and teeth. The remaining one percent is found in the blood.

Two types of bone found in the body—cortical and trabecular. Cortical bone is dense and compact. It forms the outer layer of the bone. Trabecular bone makes up the inner layer of the bone and has a spongy, honeycomb-like structure.

Bone Remodeling

Throughout life, bone is constantly renewed through a two-part process called remodeling. This process consists of resorption and formation. During resorption, special cells called osteoclasts break down and remove old bone tissue. During bone formation, new bone tissue is laid down to replace the old. Several hormones including calcitonin, parathyroid hormone, vitamin D, estrogen (in women), and testosterone (in men), among others, regulate osteoclast and osteoblast function.

The Bone Bank Account

Think of bone as a bank account where you deposit and withdraw bone tissue. During childhood and the teenage years, new bone is added to the skeleton faster than old bone is removed. As a result, bones become larger, heavier, and denser. For most people, bone formation continues at a faster pace than removal until bone mass peaks during the third decade of life.

After age 20, bone withdrawals can begin to exceed deposits. For many people, this bone loss can be prevented by continuing to get calcium, vitamin D, and exercise and by avoiding tobacco and excessive alcohol use. Osteoporosis develops when bone removal occurs too quickly, replacement occurs too slowly, or both. You are more likely to develop osteoporosis if you did not reach your maximum peak bone mass during your bone-building years.

Women, Men, and Osteoporosis

Women are more likely than men to develop osteoporosis. This is because women generally have smaller, thinner bones than men have and because women can lose bone tissue rapidly in the first four to eight years after menopause because of the sharp decline in production of the hormone estrogen. Produced by the ovaries, estrogen has been shown to have a protective effect on bone. Women usually go through menopause between age 45 and 55. After menopause, bone loss in women greatly exceeds that in men. However, by age 65, women and men tend to lose bone tissue at the same rate. Although men do not undergo the equivalent of menopause, production of the male hormone testosterone may decrease, and this can lead to increased bone loss and a greater risk of developing osteoporosis.

Section 2.2

Why Do We Have Bones?

This section includes text excerpted from The Basics of Bone in Health and Disease, National Center for Biotechnology Information (NCBI), 2004. Reviewed January 2019.

The bony skeleton is a remarkable organ that serves both a structural function—providing mobility, support, and protection for the body—and a reservoir function, as the storehouse for essential minerals. It is not a static organ, but is constantly changing to better carry out its functions. The development of the bony skeleton likely began many eons ago, when animals left the calcium-rich ocean, first to live in freshwater where calcium was in short supply, and then on dry land where weight bearing put much greater stress on the skeleton. The architecture of the skeleton is remarkably adapted to provide adequate strength and mobility so that bones do not break when subjected to substantial impact, even the loads placed on bone during vigorous physical activity. The shape or structure of bone is at least as important as its mass in providing this strength.

The skeleton is also a storehouse for two minerals, calcium and phosphorus, that are essential for the functioning of other body systems, and this storehouse must be called upon in times of need. The maintenance of a constant level of