As mentioned my previous post, ‘The Early Signs and Risk Factors of Osteoporosis,’ I mentioned that our maximum bone density peaks at around the age of 30-35 (25 for some individuals). In this article we are going to explore the stages of Osteoporosis, and the biological processes that govern bone density. Understanding these processes is key to understanding the nature of Osteoporosis and Osteopenia.
Osteoblasts vs Osteoclasts
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Osteoblasts and Osteoclasts are two variants of bone cell (osteocytes) serving different purposes. Osteoblasts are cells that make bone in response to both the mechanical stresses placed on our bones and additional growth factors such as hormones. Osteoclasts are cells that break down and resorb bone. They are like little demolition trucks and recycling plants. These cells work in tandem to continually remodel our bones as we grow and move through the various stages of our lives. At approximately 30 years of age we can expect to have regenerated five complete skeletons.
Peak Bone Density and the First Stages of Osteopenia and Osteoporosis.
Our individual peak density occurs once the rate of new bone being remodelled by osteoblasts is greater than the rate of breakdown via the osteoclasts. Between the age of 30 to 35 (25-30 in some individuals) the rate of bone deposition slows down to be almost equal to the rate of breakdown. This state of equilibrium maybe considered the first stage of declining bone mineral density, a process that can be referred to as leaching.
The Second Stage of Osteopenia and Osteoporosis.
Somewhere between the age of 25 and 35 the rate of bone breakdown will eventually outweigh the rate of bone deposition. Bone loss begins to occur at an approximate rate of 0.25% a year and is variable depending on many genetic and environmental factors.
This may be considered the second stage towards osteopeinia and/or osteoporosis. It is important to understand that this is a perfectly normal part of the aging process. However, unlike discovering your first wrinkle or a few stray grey hairs the age related changes of bone are not visible. It is also important to note that just as some individuals may have more grey hair or more wrinkles at an earlier age than others, the rate of bone loss can also vary depending on our genetic makeup as well as environmental and dietary factors.
The Third Stage of Osteopenia and Osteoporosis.
From the age of 45 to 55 the breakdown of bone occurs at a faster pace in women due to the effects of menopause and associated reduction in the hormone oestrogen which is important in maintaining the health of all body tissues including bone, muscle, ligament and tendon.
Women may lose as much as 10 to 20% of their bone density around the five or so years of menopause. Some may lose as much as 30%. It is not uncommon for women to lose up 2% of bone mineral density a year during menopause. Men undergo similar changes in bone density at around the age of 60 to 65 when they experience a decline in the hormone testosterone. This period of hormone related changes may be considered the third more vulnerable stage of reduced bone density. Associated with this third stage is an increase in fragility fractures where stress on a bone, previously considered normal in younger years, may now be enough to cause a fracture. Tripping over a pet, banging into a door, even running more than usual or bending forward to pick up something heavy like a bucket of water may create enough stress to cause a fracture where the impact is greatest.
It is important to know that around 50% of individuals over 50 in Australia who sustain a fracture have underlying osteoporosis. Equally important to note is that 50% do not. Having a T score of less than -2.5 (the formal definition of osteoporosis) does not mean you will sustain a fragility fracture. It does mean you have a higher risk though. If this score is combined with poor balance combined with a significant loss of muscle mass – something referred to as sarcopenia – the risk of falling and sustaining a fracture is
much higher.
Professor Robin Daly who specialises in exercise and the ageing (Deakin University) is adamant that
‘Osteoporosis does not equal fracture’. A combination of osteoporosis + poor balance + loss of muscle mass and strength is what we all really want to avoid if we are to reduce our risk of fragility fracture.
(For a basic understanding of T and Z scores see the link below)
The Fourth Stage of Osteopenia and Osteoporosis.
Without any intervention, osteoporosis can progress to stage four. During this stage the effects of significant bone loss become visible. Softening of the bones and accumulated fragility fractures, especially in the spine, results in deformity. Anterior wedging of the vertebral bodies of the spine causes the rounded bent over appearance (kyphosis or often referred to as a dowagers hump) we have all observed in some frail older individuals. Associated with the deformity is pain and more and more
difficulty managing normal activities of daily living such as getting into and out of a car, chair or bed, climbing stairs, hanging out washing and reaching overhead etc.
Fortunately there has been ongoing research in the management of osteoporosis including prevention as well as management. The exciting thing is this has not only included medical intervention with drugs but also the effects of resistance training on increasing bone density. The Griffith University in Queensland is currently conducting research in resistance training without injury in women over 60 and the results are very promising. While, the Bone Clinic, (Coorparoo Brisbane) is putting into practice many of the principles of this resistance training and, to bring it to a personal level, I am undergoing such specific
training myself. I hope to report good news in August this year.
Understanding your DXA scan results for detecting osteoporosis
So you have had a bone density scan and given a report with a T and Z score for hip
and spine. What does the T score and Z score actually mean to you? According to Osteoporosis Australia the bone density scan – referred to as a DXA scan (Dual Energy X-ray Absorptiometry) is really the ‘Gold Standard’ test for osteoporosis or osteopenia. A T score of 0 means you have no bone loss compared to that of a 30 year old person of the same gender. A T score of -1 indicates a bone loss of 1 standard deviation below that of a 30 year old healthy person of the same gender.
So what does this one standard deviation really mean? It simply means a bone loss of 10%. For example a T score of -2 means a loss of 20% and -2.5 would mean 25%. A T score of -4 means a loss of 40% and this would be of some concern. It is important to understand a T score of -1 and above is perfectly normal once over 50. A T score between -1 and -2.5 indicates lower than normal bone density for age –
this is referred to as osteopenia. A score lower than -2.5 indicates significant bone loss – 25% or more and this is classified as osteoporosis.
To put things into perspective, it would be abnormal at age 50 or more, for example, to have a T score of 0. It would be as unusual as a 50 year old having not one wrinkle. A certain amount of bone loss is a perfectly normal process of ageing. It is important to understand this.
The Z score gives an indication of bone density compared to a healthy person of the same age and gender. A Z score of -2 in a 50 year old would indicate a 20% greater loss of bone density compared to what the expected ‘normal’ bone loss for a 50 year old would be. A Z score of -2 is significant and requires investigation into the reason for bone loss other than normal aging.
DXA scans are usually done on what are considered the most vulnerable bones in the body. These are the lumbar spine and neck of femur. The wrist is also a vulnerable area and may be included in the test. Do not be concerned about the amount of radiation you could be exposed to during a DXA scan as it is far less than a normal chest x-ray.
It is useful to know that the small portable bone scan machines available in some pharmacies and travelling vans only measure the density of distal bones in the body such as the heel or finger. They can give some indication of bone density in these areas but they do not replace the gold standard test provided by a central scanning device in a hospital or private radiology practice. If you are concerned about a test result from one of these portable devices follow it up with your health professional.
Remember – some bone loss is perfectly normal. From age 30 when peak bone density occurs, there is a gradual decline in bone density as the percentage of bone resorption increases and bone formation decreases.
The major consequence of bone loss as we age is fracture. Having osteoporosis in itself does not mean you will have a fracture. If it is combined with significant muscle loss and poor balance (something known as sarcopenia) there is an increased risk of fracture.
References
- International Osteoporosis Foundation
- Osteoporosis Australia
- Physiology of Bone Loss Radiology Clinic North Am. 2010 May:48 (3): 483-495 Professor Robin Daly – Department Exercise and Aging Deakin University (Seminar University Canberra 2016)
