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Importance of Bones

Bones and the skeleton play many important roles in the body, including:

• Storing and supplying calcium as needed for all the cells and organs of the body when dietary sources are not adequate
• Providing our bodies with support and muscle attachments, which allow us to move and use our limbs, trunk, and head
• Enclosing and protecting our vital organs
• Providing space for bone marrow, where all types of blood and bone cells are made

Bone cells can respond rapidly to their environment.

• Increased stress, such as weightbearing exercises, can strengthen the structure of individual bones to resist fracture.
• Lack of stress, such as bed rest or weightlessness in space, can rapidly weaken bone.

While the outside of a bone looks like rock, the inside more closely resembles lacy coral surrounded by a hard, thick shell. Unlike rock, bone is living tissue that is constantly changing. Complex functions occur within what appears to be a solid structure.

In general, bones are made up of spongy, mesh-like cancellous bone covered by hard, compact cortical bone. Bone marrow is found within the spongy bone at the center of many bones.

Reproduced and adapted from JF Sarwark, ed: Essentials of Musculoskeletal Care, ed 4. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2010.

Bone Remodeling

• The body's skeleton forms and grows to its adult size in a process called modeling.
• The skeleton then completely regenerates — or remodels — itself about every 10 years. Remodeling removes old pieces of bone and replaces them with new, fresh bone tissue. This process keeps the bone and its cells healthy and strong, and it allows the bones to supply calcium to the body.

Keeping the skeleton in good repair requires a balance between removal and replacement of bone tissue.

• In young, healthy adults, the amount of bone removed and replaced is about the same. This is called balanced bone remodeling.
• As we age, the remodeling process can shift out of balance, resulting in loss of bone structure and strength. This can lead to bone diseases, including osteoporosis. Learn more: Osteoporosis

Enlarged photographs of the cancellous bone inside a vertebral bone in the spine. (Top) Healthy, spongy cancellous bone with thick interconnected architecture (Bottom) Cancellous bone loss caused by osteoporosis with weak architecture. This weakened bone is at an increased risk for fracture.

Reproduced from Einhorn TA: The structural properties of normal and osteoporotic bone. Instr Course Lect 2003; 52: 533-539.

Each year, approximately 2 million older Americans sustain fractures because of weak bones, leading to temporary or permanent disability, and even death. The incidence by 2025 is predicted to be 3 million.

There are 300,000 hip fractures in the U.S. yearly, and half of these people do not regain their pre-fracture activity level. Fortunately, there are things you can do to maintain and even improve your bone strength:

• Understand your individual risk for fracture. This is based on any risk factors you have — such as age, smoking or vaping, a history of falls, diabetes, inflammatory and autoimmune diseases, certain medications that cause bone loss, and your bone density. Ask your doctor if you need a bone density test.
• Understand your individual risk for bone loss. Genetics plays a large role in bone health, and some people have genetically determined high rates of bone turnover after menopause or with aging. Bone metabolism testing can provide additional information about your risk for fracture. It can also be used to ensure that you are responding to osteoporosis medications.
• Be active every day.  Strength-building and weightbearing activities help build strong bones. Children should exercise at least 1 hour each day, and adults should get 30 minutes of daily activity. Learn more: Exercise and Bone Health
• Maintain a healthy weight.  Older adults who are overweight have a higher risk of falling. Being underweight raises the risk of bone loss and fractures.
• Get enough calcium and Vitamin D. The health of our bones depends on steady stream of nutrients, most calcium and Vitamin D. Learn more: Calcium, Nutrition, and Bone Health and Vitamin D for Good Bone Health
• Do not smoke.  Smoking can reduce bone mass and increase your risk for a broken bone, and nicotine inhibits bone-forming cells. Studies also show that vaping may increase the risk of fractures and osteoporosis, and that people who smoke cigarettes and vape have a higher risk of fractures than people who only smoke cigarettes. Learn more: Smoking and Musculoskeletal Health
• Limit alcohol use. Heavy alcohol use reduces bone mass and increases your risk for falls and broken bones.
• Reduce your risk of falling. Exercise can help reduce your risk of falling. There also are many changes you can make in your home to help prevent a fall. Remove obstacles and add safety features — such as grab bars and non-slip mats — where needed. Learn more: Guidelines for Preventing Falls
• Consider bone-boosting medications. In addition to calcium and Vitamin D supplements, there are many medications available to help slow bone loss and increase bone strength. There are also medications that can build completely new bone and repair lost architecture. Talk to your doctor about these methods for protecting your bones. Learn more: Osteoporosis Prevention and Treatment