In the last three posts, we opened the discussion of what happens to our bodies as we age and then we delved into the effects of aging on our muscular and nervous systems.
Today’s post is going to be significantly denser and more detailed as we explore the impact of aging on our bones and what we can do to slow down and lessen the impact of this process.
Is there a Problem with Bone Health as We Age?
As a matter of fact, there is. The Department of Health and Human Services was assigned by the Office of the General Surgeon to compile a report on the current status of bone health and bone disease of the American population. According to their report, which was completed in 2004, bone disease is on the rise, but it is preventable, and information is now available to the public. Regrettably, “much of what could be done to reduce this burden is not being done today, largely due to a lack of awareness of the problem and a failure to apply current knowledge. In fact, many in the public and even the medical community believe that osteoporosis is a natural consequence of aging and that nothing can be done about it. This view must be changed” [1]. This 400+ page report contains an extensive review of all the current research on bone physiology as it relates to healthy versus diseased bones and how to prevent bone disease.
While I imagine that reading this report would be fascinating for a few of you, I am sure that most of us can think of many, many other things that we would rather be doing. For right now, it is enough to state that, your overall health and well-being include good bone health.
I hope this brief discussion of bone physiology, nutrition, physical activity, and fall prevention will give you the knowledge needed to prevent bone disease and fractures in the future. Remember, all that you learn now can be shared with those you care about in an effort to help them avoid or lessen the devastating results of bone disease.
Bones are Living Organs
Bones are alive! Bone is a living organ that is constantly remodeling itself. It is constantly being remodeled to adjust for the stresses that we place upon it. There are special bone cells (osteoclasts) that function to tear down the old bone to make room for new bone, and there are other bone cells (osteoblasts) that function to form new bone. Bones are also responsible for creating vital red blood cells for our body, which takes place in the marrow inside the shaft and ends of the bone.
I would like to stop and emphasize that the body is an amazing creation. I am only reviewing the basic physiology of bone in this section because it is so complex that even the scientists are still trying to understand many of the unanswered questions about bones.
The Role of Bones in the Body
Bones come in all shapes and sizes. Compare the skull bones with the leg bones for example. All bones have an outer layer called the cortical bone and an inner layer called trabecular bone. Cortical bone is hard and very compact or dense while trabecular bone has the appearance of a bee hive or honeycomb. Trabecular bone has two main functions: 1) to allow mineral exchange, as the honeycomb shape provides a large surface area for the body to draw minerals from, and 2) to help to maintain skeletal strength and integrity for areas of bone that undergo the most stress from motion and weight-bearing.
Bones provide key functions for our bodies that we all should be aware of as they:
- Provide protection to vital organs
- Provide a sound foundation for tendons and ligaments to attach themselves, which is necessary for movement
- Store essential minerals that are needed for normal functioning of bodily organs and tissues.
- Produce all blood cells, including the ones that fight infection.
Modeling, Remodeling, and Resorption
Modeling is the process of making bone at one site and then removing bone from another site in the same bone. Remodeling is the process of removing and replacing bone at the same site in a bone.
Research shows that during different stages of life the body adjusts its modeling and remodeling priorities. For example, children’s bones grow on the outer surface while resorption, the process by which bone is broken down and the minerals are released into the blood, is occurring on the inner surface.
In contrast, during adolescence, the bones get thicker due to formation of bone on both the inner and outer layers of the bone.
For those of us who are well beyond adolescence, the body removes bone from the inner surfaces and places it on the outer surfaces to attempt to compensate for the natural thinning that occurs with aging.
Loss of Bone Density
When a bone loses its density, it becomes porous or full of holes. As a result, the strength of the bone decreases, making it more at risk for fracture. This is known as osteopenia. Osteopenia is a precursor to osteoporosis which is a more severe form of bone disease.
After menopause, bone resorption rates increase over the next 4-8 years, leading to a 5-10% loss of the dense (cortical) bone found in the shafts of long bones, pelvis, skull, and flat bones as well as a loss of 20-30% of spongy (cancellous or trabecular) bone found mainly in the vertebrae (spine), ends of long bones, and flat bones such as your sternum and ribs. In both men and women, there is a 20-25% total loss of bone after menopause has ended. It is here in the spongy regions of the bone that osteoporosis usually occurs.
Aging and Osteoporosis
Osteoporosis is the most common bone disease affecting Americans. Statistics from the Department of Health and Human Services estimate that by 2020, half of all-American citizens older than 50 will be at risk for fractures from osteoporosis and low bone mass. In 2004, 10 million Americans over the age of 50 had osteoporosis, and another 34 million were at risk for developing osteoporosis. Each year, roughly 1.5 million people suffer a bone fracture related to osteoporosis, which often leads to a deterioration of that person’s physical and mental health. Did you know that 20% of senior citizens (20 out of 100) who suffer a hip fracture will die within one year? That is motivation enough for me to want to continue being physically active and to encourage my family members to do the same.
Those statistics are astounding. We all must make our health and that of our family and friends a top priority. Sadly, current research shows that less than 45% of all Americans between the ages of 18-24 engage in regular leisure time physical activity. And of those 45% who do participate another 10% stop being active after the age of 25 years. Only 30% of adults over the age of 65 continue to be physically active. It is even worse for females compared to males. Women, young and older, truly do need to “step it up.” One study showed a 36% decrease in the risk for hip fractures in those who were physically active [2, 4, 5]. A 41% decrease in risk for hip fractures was noted in postmenopausal women who walked 4 hours per week compared to those who only walked for 1 hour per week.
Preventing Osteoporosis
To combat the onset of osteoporosis, it is important that we take steps to decrease the rate at which bone resorption occurs. To begin, eating a well-balanced diet including foods high in calcium, phosphates, and proteins is critical for good bone health. Being physically active places healthy stress on the bones and muscles which triggers a cascade of events to encourage more bone growth and replacement instead of reabsorption. Additionally, it is important to remove factors that negatively contribute to osteoporosis, namely smoking and excessive alcohol consumption. Moreover, we can work to manage conditions such as anorexia nervosa, as well as diseases such as Crohn’s and Celiac which affect the gastrointestinal system and therefore nutrient intake.
Aging and Osteoarthritis
Aging takes a toll on the joints as well. Osteoarthritis refers to the cartilage at the end of a bone that begins to break down like pot holes in a road. Pitting of the cartilage exposes the ends of the bone, which contain nerves and blood vessels. Inflammation occurs when the end of the bone gets irritated. Rest combined with anti-inflammatory treatment can calm down the inflammation, but unfortunately, many do not progress beyond this step to actually treat the cause of the symptoms.
The research reveals that once the inflammation is reduced, the best medicine for osteoarthritis is low impact activities, such as walking, swimming, mild to moderate strengthening, and other light aerobic activities followed by rest and cold packs to control the inflammation. Approximately 50% of persons over 65 years of age suffer from some degree of osteoarthritis, with females being affected more than males.
Other contributors and risk factors that have been shown to increase the likelihood of osteoarthritis are obesity, previous joint injuries, certain types of infections, inactivity, genetics, and occupations that require repetitive movements such as squatting.
Rheumatoid arthritis, a chronic inflammatory disease that attacks the synovium, the soft tissue that lines the spaces of the joints and results in joint damage, chronic pain, decreased function and disability, is also a known contributor to osteoarthritis.
Bones: Our Bodies’ Savings Accounts
Bones have been referred to as a savings account in the bone bank where essential minerals such as calcium and phosphate are stored for a time of need. Small crystals containing calcium and phosphate are called hydroxyapatite. Hydroxyapatite binds with collagen protein to make strong bones. When tissues such as muscles and nerves require more calcium and phosphorus to function properly, they signal hormones to be released into the blood, which then go to the bone bank to make a withdrawal and carry them back to the tissues in need. When the bone bank account is overdrawn, the bones do not have enough reserves for themselves and the health of the bones decreases and makes them more susceptible to fractures. So, this begs the question: what can we do to maintain healthy amounts of essential minerals in our bone bank accounts?
Deposits into this bone “bank” can be made in two different manners. First is the type of diet that we establish. Second is the amount of exercise or physical activity that we perform.
The Role of Diet
Diet is an important part of healthy bones. Consuming foods rich in calcium, vitamin D, and protein give the bones the nutrients needed to make new bone. Sources of calcium may include low-fat milk, yogurt, ice cream and cheese, tofu, salmon and sardines (with the bones), and dark green leafy vegetables, such as spinach, broccoli and collard greens, orange juice, cereal, bread, and nuts such as almonds. Vitamin D may be found in fortified milk, cheese, butter, fish, fortified cereal and the exposure to the sun. The National Institutes of Health recommend exposure to the sun three-times per week for 10-15 minutes as a good source of vitamin D. Protein is an important nutrient that builds muscles and bones and provides energy. The healthiest proteins are the leanest. This means that they have the least fat and calories. The best protein choices are fish or shellfish, skinless chicken or turkey, low-fat or fat-free dairy (skim milk, low-fat cheese), and egg whites or egg substitute. The best red meats are the leanest cuts, loin and tenderloin. Other healthy options are beans, legumes, lentils, peanut butter, and soy foods such as tofu or soy milk [1, 3].
The Role of Exercise
Healthy bones are necessary for the prevention of disease and maintenance of healthy bones. As you are now aware, osteoclast cells break down bone to make way for new bone. Healthy bones have a happy balance between the amount of bone being broken down (resorption) and the amount being replaced. Weight bearing bones are constantly being reshaped to handle the everyday stresses placed upon them.
A scientist, name of Julius Wolf, discovered that bone will remodel itself according to the amount of stress and the direction of stress placed upon it. As we walk, lift, bend, sit, and sleep, our bones are remodeling themselves to lay down more bone where heavier stress is placed and remove bone in areas of less stress. This became known as Wolf’s Law. Chemical signals from within the bone cells called osteocytes tell the bone where to place the needed minerals to handle the stress of the physical activity. In other words, “form follows function” or shape follows stress. Scientists believe that chemical signals from within the network of bone cells called osteocytes inform the osteoblasts where to place the needed collagen and minerals to handle the stress. If a person is sedentary or inactive, the bones do not get stimulated sufficiently. What happens then is that osteoclasts remove the bone and store it away for other tissues to use rather than rebuilding and strengthening the bones. The longer a person is sedentary, the higher the risk of bone fractures.
How Can We Maintain Healthy Bones?
There are several factors involved in the maintenance of healthy bones, such as diet, blood hormones, and the amount of physical activity or stress placed upon them.
The greater our level of activity the more the body recognizes the need to absorb more calcium, phosphorus and other nutrients to continue to fortify the bone walls.
So what can we do to promote healthy bones? There are two major contributors that affect bone health and all the research tells us what we already know in our hearts and minds. We must eat a balanced diet and participate in physical activity. As much as 50-90% of our bone structure depends upon the genes that our parents gave to us. The other 10-50% will depend upon what we eat and how physically active we are. It is up to us!
- cdc.gov
- McArdle WD, Katch FI, Katch VL, eds. Exercise physiology. 4th ed. Baltimore, MD: Williams & Williams; 1996.
- Paddon-Jones D, Campbell WW, Jacques PF, Kritchevsky SB, Moore LL, Rodriguez NR, van Loon Protein and healthy aging. The American Journal of Clinical Nutrition, Volume 101, Issue 6, 1 June 2015, Pages 1339S–1345S.
- Feskanich D, Flint AJ, Willett C. Physical activity and inactivity and risk of hip fractures in men. American Journal of Public Health. 2014 (April); 104(4): 75-81.
- Feskanich D, Willett W, Colditz G. Walking and Leisure-time activity and risk of hip fracture in postmenopausal women. JAMA. 2002; 288 (18): 2300-2306.
