As mentioned in 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 the key to understanding the nature of Osteoporosis and Osteopenia.
Osteoblasts vs Osteoclasts
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 may be 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 osteopenia 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, running more than usual or even 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. 1
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 and/or with 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’. 1
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 fractures.
You can find out more about T and Z scores by reading our tutorial “Making Sense of Your DXA Scan Results for Detecting Osteoporosis.”
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.
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.
1. Professor Robin Daly – Department Exercise and Ageing Deakin University (Seminar University Canberra 2016)