Pointing the bone at osteoporosis
Key text
This topic is sponsored by Milk Marketing (NSW).
Think this is a disease that only affects old people? The reality may be closer to the bone than you think.
The term osteoporosis literally means holes in the bones. 'Osteo' is derived from the Greek word for bones and 'porosis' is from the Greek word for passage or hole. Many people think it is an old people's disease, being most common in women over 40 (although this is hardly old) and men over 60.
Osteoporosis does become more common as people get older. Bone loss is a natural part of ageing, and all human beings would eventually develop the disease if they lived long enough.
But young people of either sex shouldn't be complacent. You, too, will one day be long of tooth and thin of hair. And medical scientists say that what we do in our youth may have an important effect on our chances of avoiding the disease.
The extent of the problem
A major study involving almost 2000 people near Dubbo in New South Wales has provided some insight into the extent of osteoporosis in Australia. It estimated that a staggering 60 per cent of women and 30 per cent of men over the age of 60 suffer from a broken bone due to osteoporosis. Any bone in the body is at risk, but some of the most common breakages occur to the hip, forearm, ribs, spine and legs, and they may occur from incidents as trivial as bumping into a door or tripping over a rug. The direct costs associated with treating osteoporotic fractures in Australia are estimated to total nearly $800 million a year.
Osteoporosis can be a very debilitating and often painful disease: imagine reaching the age of 40 and being unable to play sport, take shopping bags from a car or lift a baby from its cot. It can lead to death: one study in Sydney reported that people who had suffered a hip fracture in the previous 12 months were five times more likely to die than were people in the corresponding age group who did not suffer a hip fracture. About one-quarter of people with hip fractures remain in nursing homes for the rest of their lives.
The problem of osteoporosis is growing as the percentage of old people in society increases. For example, the number of hip fractures in Australia is predicted to increase from 14,600 in 1994 to 20,900 in 2010 in the absence of effective prevention and treatment regimes.
Who is at risk?
Medical scientists have identified a number of factors that appear to increase the risk of osteoporosis. You are more likely to suffer from the disease if:
- you are female;
- you are thin and small-boned;
- there is a family history of the disease;
- you are Caucasian or Asian;
- you eat few or no dairy foods;
- you do not exercise regularly;
- you smoke;
- you drink more than two or three alcoholic drinks per day;
- you drink more than six strong cups of tea or coffee per day;
- you suffer from irregular periods;
- you had an early menopause;
- you are post-menopausal; or
- you take medication that limits calcium absorption.
Why does osteoporosis occur?
To understand how osteoporosis occurs, we need to understand the process of bone building.
Bone formation and shaping starts in the womb and continues throughout our lives. Cells called osteoblasts add bone while others, called osteoclasts, break it down. Certain supplies are needed for adequate bone development, including the minerals calcium and phosphorus and a range of hormones and vitamins (vitamin D, in particular, plays an important role in regulating calcium absorption from food). Calcium and phosphorus must be obtained from the food we eat, while hormones are produced by glands in various locations in the body. Most vitamin D is created by the skin when exposed to sunlight and is also present in some foods.
Osteoblasts use calcium and phosphorus supplied by the bloodstream to produce a hard mineral salt called calcium phosphate. They deposit this chemical outside their cell walls until eventually they become trapped by their own endeavours. At this point they stop building bone, but they continue to attend to the nutritional needs of the bone around them. They are then known as osteocytes.
Osteocytes maintain contact with other osteoblasts and osteocytes via a network of tunnels, which also act as passages for nerves and blood vessels. Bone formation thus produces a honeycomb structure, where the solid material is perforated by tunnels. Bones usually comprise a hard outer wall, where the honeycomb is tightly packed and bone is laid down in rings, and an inner tissue where the honeycomb is considerably less dense.
Peak bone mass
During the early phases of our lives, more bone is added and maintained than is resorbed into the bloodstream. By early adulthood, we reach what is known as peak bone mass, which is the maximum density achieved by our bones. After about 35 years of age, even though bone formation still occurs, our bone mass slowly declines due to a process called demineralisation (simply, the net loss of calcium). The hard outer bone becomes thinner and more brittle, while the softer inner bone develops larger holes. Below a certain threshold of bone mass, we become osteoporotic and prone to frequent bone fracture.
Making deposits at the Bone Bank
Building up our calcium reserves is a bit like putting money aside for a rainy day. In our early years, we build up 'funds' by depositing calcium on our bones. The more we deposit the more we have available, should we need it, as we grow older. Medical scientists believe that by 'saving' as much calcium as we can in our early years (Box 1: Ensuring a healthy balance at the bone bank), we may reduce the likelihood of suffering from osteoporosis – a physical kind of bankruptcy – in our later years.
Thieving from the bank: how calcium is lost
A slow loss of calcium – about 1 per cent a year from our middle years onwards is a normal part of ageing. If we have sufficient reserves and the loss is not accelerated for any reason, most people are unlikely to suffer from osteoporosis until they are very old, if at all.
Accelerated calcium loss can occur for many reasons: we might smoke and drink too much, we might not exercise sufficiently, we might have some other disease that reduces our ability to absorb calcium, or we might be genetically predisposed to it. There is another key reason that affects all women: menopause.
Why women are most at risk
Menopause occurs in a woman at about 45 years of age, when the production by the ovaries of the sex hormone oestrogen gradually declines. This has many effects, including the gradual cessation of menstruation (the periods).
Oestrogen is thought to play a role in maintaining bone mass by slowing the process of bone breakdown by osteoclasts. As oestrogen levels fall, bone breakdown accelerates.
The decline in oestrogen levels due to menopause is the main reason that more women than men suffer from osteoporosis. Menopause is not the only reason: women may also suffer a decline in oestrogen levels if their ovaries have been surgically removed (as often happens in a hysterectomy), or through severe dieting or excessive exercise. Women also have a lower peak bone mass than men so they have less bone to lose. They often live longer, too, which increases the chance of developing osteoporosis.
Can osteoporosis be cured?
Once somebody has osteoporosis, they have it for life. Treatments and lifestyle changes can slow the rate of bone loss and fracture rates, but none has yet shown a capacity to restore bone mass to above threshold levels. Scientists continue to investigate the potential of gene therapy for treating the disease.
Some drugs may be useful in preventing the onset of osteoporosis and reducing its impact in people suffering from the disease. Many women who enter menopause receive hormone replacement therapy to counter the decline in oestrogen levels. This treatment, while somewhat controversial, appears to have a significant effect on limiting bone loss (Box 2: Hormone replacement therapy).
Similarly, compounds known as bisphosphonates are drugs that are thought to inhibit bone resorption and therefore reduce the risk of fracture. Correcting a vitamin D deficiency, which is common in old people living in institutions (where they may not receive adequate exposure to sunlight), has also been shown to reduce fracture rates.
A recent study showed that another possible treatment, calcium supplements, significantly reduced the risk of fracture. In fact, the reduction in risk was greater than could be explained solely by an increase in bone density. According to the scientists conducting the study, this suggests that calcium may play an additional role, perhaps by affecting muscles and thereby decreasing the risk of a fall.
Be a bone-head!
Since osteoporosis is a disease with no cure, and since it can substantially reduce quality of life for many of your later years, it makes sense to take precautions. Fortunately, this isn't too difficult, although it does involve a few lifestyle choices (eg, regular exercise, balanced diet, no smoking). And those who argue against making such choices? Well, they hardly have a leg to stand on.
Posted August 1998.