Bone health

How bones work — the nature of healthy bone

by Dr. Susan E. Brown, PhD

I’ve studied bone health for over twenty years, and our human bones continue to fascinate me. Spontaneously, without any thought or effort, bones build and repair themselves throughout the lifespan. And even though bones naturally tend to get thinner as we age, they normally are able to maintain enough bone mass and strength to withstand the stresses and strains of life well into old age.

So why is it that modernized countries are experiencing a virtual epidemic of poor bone health?

It wasn’t always this way. In fact, osteoporosis was extremely rare 100 years ago. But in the present day, we frequently hear that one out of three women will suffer from a bone fracture related to osteoporosis. And this has nothing to do with our longer lifespan.

If we step back to gain an understanding of how healthy bones work and learn to appreciate their role in the wellness of the entire body, we can help ourselves out of this bone crisis. And as we learn to work with nature to support our bones, I’m positive the rates of osteoporosis and fractures will drop. So let’s take a closer look at how healthy bones do their work and what you can do to support them naturally.

The architecture of bone

Bone has many important jobs within our bodies and so it requires a multifaceted structure. The many parts that make up our bones give them strength and resistance, yet also provide flexibility. The hip, for example, must be strong enough to withstand up to 600 pounds of force, yet it must also be flexible enough to tolerate twisting and bending without breaking. How does it do this? Here is a closer look at what bone is made of:

Collagen. Collagen is an elastic living matrix made of protein, and it is central to the diverse nature of bone. Collagen takes up about 22% of all bone. Crystalline minerals are deposited on its honeycombed protein matrix. The collagen imparts flexibility and the crystalline minerals impart rigidity and strength. Most of the research done on osteoporosis has focused on the inorganic bone mineral crystals and bone mineral density (BMD). But I believe that the new frontier in bone health will involve study of collagen.

Bone collagen feeds on an adequate supply of many nutrients, such as vitamin C, sulfur, copper, zinc, manganese, boron and others, while inflammatory agents like steroid medications or nonsteroidal anti-inflammatory medications can damage collagen and connective tissue.

Cortical and trabecular bone. The unique architecture of bone provides for two types of bone structures — one called cortical or compact bone and another called trabecular bone. Cortical bone is the dense compact bone seen on the outside. It makes up the majority of our total bone (80%). It forms a tough outer protective layer, and some 80-90% of it is calcified.

Trabecular bone makes up the other 20% of bone. It has a much looser lattice weave and appears spongy. Only 15-25% percent of trabecular bone is calcified, the rest is marrow. Because trabecular bone has more surface area, it undergoes more turnover than cortical bone and loses more protein matrix and imbedded minerals. It’s not too surprising then that fractures typically occur in bones with high trabecular content. Your spine and wrists are mostly trabecular bone, while your arms and legs are mostly made up of cortical bone.

Osteoclasts and osteoblasts. Specialized bone cells, known as osteoclasts and osteoblasts are responsible for the breakdown and rebuilding of bone that is constantly occurring. Osteoclasts break down small bits of bone, releasing calcium, phosphorus, magnesium and other nutrients for use in the blood. Each day, some 360 mg or more of calcium are dissolved from the bone and deposited in the blood. Each year, 20% of an adult’s bone calcium is replaced. Osteoblasts carry out the reverse process, absorbing minerals and placing them back into bone while building new segments of bone. These opposing processes must be carried out in precise balance to maintain a stable bone mass.

Continual growth and repair — the life cycle of bone

Your bones continue to grow and repair themselves throughout life. However, a woman experiences peak bone mass — a state of maximum bone density — when she is between 25 and 30 years old. This is when your bones are strongest and densest. Studies done in the United States suggest that a woman might lose up to 38% of her total peak bone mass over a lifetime. Some women, however, may lose little to no bone mass throughout life. Whether or not you lose bone depends on a range of factors, including your nutrition, exercise, genetics, and lifestyle. (For more on risk factors, see our risk factors section.)

Because of the wear and tear it undergoes, bone needs to heal and repair itself constantly. Unique self-repair mechanisms have evolved in our bones for these purposes. The repair processes are conducted by osteoclast and osteoblast cells. And it is much like highway repair. A damaged area of the road is picked for repair; the silt is excavated removing the old weakened asphalt, and then new material is put down. Bone heals and remodels itself in a similar fashion. This self-repair capability is extremely important because imbalances that result in more bone being broken down than laid down can cause osteoporosis.

Remodeling is a complicated process, and more research is needed in this area. But we do know that both systemic hormones and local factors play important roles in breaking down and forming new bone. The systemic hormones at work include:

• Parathyroid hormone
• Calcitonin
• Thyroxin
• Insulin
• Growth hormone
• Vitamin D (synthesized and activated by the kidney)
• Glucocortical adrenal hormones
• Estrogen
• Androgen

Some of the local factors involved in bone remodeling include:

• Growth hormones
• Vitamin B2
• Microglobulins
• Transferrin

The key bone building nutrients

Science now verifies what common sense would dictate: we can build bone best when we supply our bodies with not just calcium, but all the necessary bone-building nutrients.

In a breakthrough study done in 1992, researchers found that bone loss can be halted in women without drugs by simply supplementing the diet with certain minerals. One group of the study received a placebo pill, and another group was put on 1,000 mg of calcium citrate-malate. A third group was given 15 mg of zinc, 5 mg of manganese, and 2.5 mg of copper. The fourth group was given the same amounts of zinc, manganese and copper as the third group, plus the same calcium as the second group. Women in the last group taking the most complete supplemental program gained a significant amount of bone mass while those on just calcium alone remained the same. The other two groups suffered significant bone loss.

Since that landmark study, we’ve learned so much more about which nutrients serve our bones. Vitamin D and vitamin K are two essential bone nutrients that are only beginning to get the attention they deserve. Vitamin D helps us absorb calcium from the intestines. Vitamin K helps calcium, phosphorus and other minerals bind to your bone’s protein matrix. There are, however, many more nutrients involved in maintaining healthy bones, and they all work in concert. To learn more, see our article on 20 key bone-building nutrients.

The “basics” of diet — alkaline foods serve your bones

These days our bones are taking a hit in two major ways. The first has to do with our modern American diet and the industrialization of farming making it difficult to get the key nutrients our bones need from the foods we eat. The second has to do with the low-grade metabolic acidosis this modern diet imparts on our blood.

Blood works optimally at an alkaline pH just above 7.0, but with the amount of acid-forming foods we consume such as meat, processed cheeses, processed flours and fried foods, the blood shifts to a slightly acidic state. You may think slight changes in pH don’t make a difference, but unfortunately this isn’t the case. Studies document that if pH drops even one-tenth of a point, osteoclasts are stimulated, osteoblasts are inhibited and minerals are lost from the bone. These donated minerals help restore pH to the blood, but at the expense of bone strength.

To prevent minerals from leaving the bones, we can make an effort to eat less acid-forming foods and more alkalinizing foods. Most fruits and vegetables are alkalizing, as is natural sea salt. Though it may seem counterintuitive, citrus fruits, such as lemons, limes, and oranges, are very good alkaline-forming foods. Ideally, our diets should be composed of about 35% acid-forming foods and 65% alkaline-forming foods. A simple way to improve your alkaline balance is to add lemon juice to water and make that your drink of choice — it’s both alkalinizing and hydrating! (For more information on how to make your diet more “basic”, read our article on pH and bone health.)

Build muscle, build bone

It’s important to remember that we have to use our bones and muscles in order to stimulate growth. Overall skeletal strength correlates directly with total muscle mass, and individual bone strength generally correlates with the strength of the muscles attached to it. Archeologists, in fact, use bone strength and form to estimate muscle of strength of prehistoric people. The bottom line is that physical activity builds bone at all ages and bone mass maintenance is a natural response to strain loading placed upon it.

The question is: how does this happen? While the full details of how physical activity encourages and even dictates bone development are not yet totally clear, some of the mechanisms are obvious. First, exercise increases flow of nutrients, energy and information to all segments of the bone. Second, physical activity transmits pressure and tension to bone by the actions of muscles. Both of these forces appear to be mediated by electrical currents, which signal the bone cells to repair and regenerate. All exercise is good for bone, but weight-bearing exercises are best for bone growth.

Our bones strive to be no heavier than necessary. The architecture of cortical and trabecular bone have evolved to maintain the lightest possible weight required to meet the demands of the body. So it makes sense that if we put more stress on our bodies by doing more exercise, building more muscle or by gaining more body weight, our bones will strengthen. They will grow stronger in response to the demands we place on them. On the other hand, if we’re inactive and put very little stress or strain on the body, bones will react by getting lighter and thinner. In this way, the human body conforms and reacts to the challenges of its environment. The more we support this ability, the healthier we are.

Work with your bones for natural health

Each one of us was born to have strong bones, capable of remodeling themselves and regulating the give and take of calcium and other essential nutrients. If we work with these built-in mechanisms through weight-bearing exercise, nutrition and positive lifestyle changes, instead of using prescription medication to replace the body’s instincts, the result is strong bones, strong bodies and better overall health. And it’s never too early nor too late to start.

Related to this article:

References & further reading on the nature of healthy bones

 

Last Modified Date: 05/25/2011
Principal Author: Dr. Susan E. Brown, PhD