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Bone and Osteoporosis

Did you know that there are 206 bones in the human skeleton? It’s true -even though some people have a couple of extra ribs. Day in and day out our skeleton is important for many reasons. Not only does it provide the structural framework for movement but bone also serves as a mineral reserve for the blood and cells throughout our body. Furthermore, many new blood cells are formed within the marrow, which is found at the core of bone.

Roughly 12% of a young woman's body weight and 15% of a man's body weight can be attributed to their skeleton. This translates to roughly 15 lb (5½ kg) for a woman and 23 lb (11 kg) for a man. Typically when we think of what makes up bone we think of minerals such as calcium and phosphorus. However, minerals only make up 30-40% of its weight. The remaining portion of bone is collagen, and to a lesser degree, other proteins as well as bone cells, nerves, and blood vessels.

Bone is constantly being remodeled.
It’s safe to say that your bone today is different than it was in years gone by and it will be different in the years ahead. That’s because bone is constantly being remodeled by bone cells called osteoblasts and osteoclasts. Osteoblasts are responsible for making new bone protein such as collagen that provides the network for depositing calcium and phosphorus complexes. Without this protein network, mineral complexes wouldn’t have anything to cling to. For this reason the osteoblasts are said to be active in making new bone tissue and are often called “bone makers.”

Osteoclasts, on the other hand, are responsible for the breakdown of bone and are often called “bone destroyers.” Osteoclasts ooze acids and enzymes that dissolve the mineral complexes and digest bone proteins. While the actions of osteoclasts might seem destructive and undesirable, their role in bone remodeling is crucial. In addition, when bone is dissolved, the minerals can enter the blood and circulate throughout the body to cells that need them.

The activities of osteoblasts and osteoclasts occur at the same time. Therefore we are building new bone at the same time as we are breaking down older bone. This process is referred to as “bone turnover”. The factors that regulate bone turnover include various hormones (growth hormone, PTH, estrogen, testosterone, and calcitonin) as well as vitamin D. In addition, mechanical stress on bone resulting from physical activity, especially weight bearing or resistance exercise, has a strong influence on bone building.

During certain periods of our life, the activities of bone-building and breakdown can become imbalanced. This can be purposeful since the imbalance results in either a net gain or loss of bone. For example, in childhood, as bone are lengthening and growing thicker, bone building activities exceed bone breakdown activities and new bone is built. On the contrary, as we age, bone breakdown tends to be greater than building activity. This results in a slow loss of bone material and increased risk of fracture.

Osteoporosis means porous bones.
Osteoporosis is a reduction in the density of bone, which is then compromised in strength and resistance against fracture. Presenting a major public health issue, the National Osteoporosis Foundation estimates that 44 million Americans or about 55% of the people age 50 and older will be affected by osteoporosis.1 It is estimated that 10 million adults already have osteoporosis, 8 million of which are women, and as many as 34 million are estimated to have low bone mass called (osteopenia). Osteoporosis affects all races and even though it is more commonly a problem later in life, it can occur much earlier.

The primary problem resulting from osteoporosis is the greater occurrence of fractures. As many as one in two women and one in four men over the age of 50 will experience an osteoporetic related fracture in their remaining life. In fact, as many as 1.5 million new fractures are attributable to osteoporosis in the United States each year. Of these, more than 300 thousand will be hip fractures and over 700 thousand will be vertebrae fractures. Sadly, many of these fractures result in permanent immobility.

Osteoporosis is often referred to as the "silent disease" because the individual doesn’t experience symptoms until the disease progresses to a critical point. That is why early detection is crucial in preventing osteoporosis. Routine bone scans are recommended and simple heel bone assessments (which are routinely performed at health fairs and as part of work-site wellness programs) can help gauge changes over time. More advanced tools such as DXA (Dual X-ray Absorptiometry) are available at specialized medical clinics. Some spas provide a more comprehensive assessment of skeletal health.

Prevention of osteoporosis is a lifelong endeavor.
During the first few decades of our life we tend to build more bone than we break down, and as a result, bone mass is accrued. The amount of bone we accrue will depend on a variety of factors including our diet, level of physical activity, and smoking or exposure to smoke. Typically, we reach maximal bone density (MBD) by the late 20s to very early 30s. After this time, bone density seems to decrease slowly.

The decrease in bone density appears to be more substantial in women versus men. It has been estimated that a woman may lose 27% or more of her bone mineral from peak bone mass to her 70s. However, it is usually not until a person fractures a bone or complains of severe back pain that an X-ray diagnosis is made. While the focus has largely been on minerals, osteoporosis is a disease resulting from loss of bone material in general. That means, protein loss as well as minerals is part of the problem. Some scientists believe that the key to preventing osteoporosis may actually be found in preserving the collagen foundation.

A reduction in blood levels, which occurs typically after menopause (postmenopausal) is directly associated with a decrease in bone density.2 Thus, estrogen is a principal factor in the development of osteoporosis. Researchers have reported that osteoblasts "bone makers" have receptors for the hormone estrogen and estrogen also appears to decrease the activity of osteoclasts "bone destroyers". Despite these findings, the exact mechanism(s) for how estrogen protects women against excessive bone material losses is not clear. Beyond reductions in circulating estrogen in post-menopausal women, other factors can increase the loss of bone mineral. These factors include poor calcium and/or vitamin D intake as well as abnormalities in metabolism.

Smoking seems to exert a negative influence upon bone mineral content and the rate of bone mineral loss, especially in postmenopausal years.1,2 Smokers tend to have lower bone densities versus non-smokers. One reason for this occurrence is that smoking reduces blood estrogen levels. Smokers also seem to reach menopause at a younger age.

Beyond hormonal, nutritional influences, and smoking, other factors directly impact bone mineral content. Physical activity increases the mechanical stress placed on bone and stimulates a reinforcement of bone strength.2 Perhaps this effect is most obvious in the absence of any weight-bearing demands upon bone. For instance, astronauts subjected to extended periods of time in space at zero-gravity (weightlessness) experience decreases in bone density. On the other hand, regular weight-bearing exercise seems to help strengthen bone and also to slow the gradual loss of bone material as we age.

Preventing osteoporosis.
The best defense against osteoporosis is a good offense. Here are some tips: 

  • Women should supplement their diet with at least 1000 milligrams of calcium on a daily basis. After age 50 women should get 1200 milligrams daily to reduce the risk of osteoporosis.
  • Men should supplement their diet with atleast 750 milligrams of calcium on a daily basis.
  • A blend or variety of calcium from multiple sources is better than one single source
  • Make sure you are getting an adequate intake of vitamin D, phosphorus, and magnesium.
  • Get at least the recommended levels of collagen builders such as vitamin C, copper, iron and zinc.
  • Exercise regularly and include weight-bearing exercise to strengthen bone.
  • Have regular medical check-ups and ask your physician to test your bone density annually.
  • Don’t smoke or quit as soon as possible

Make bone health a priority.
You can't accomplish everything you want in life if you don't look out for your bone health. Take care of your bones- so they'll take care of you for a lifetime. 

 


  References

  1. National Osteoporosis Foundation Statistics. www.nof.org, 2006
  2. Management of osteoporosis in postmenopausal women: 2006 position statement of The North American Menopause Society. Menopause. 25, 2006  

The information presented above is for educational purposes only. It is not meant to be used to diagnose or treat any medical conditions or diseases or to substitute for qualified medical advice. Consult your physician before starting a weight management or exercise program.

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