Pointing the bone at osteoporosisThink this is a disease that only affects old people? The reality may be closer to the bone than you think.
Key text
Key textThe 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:
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.
Diet A balanced diet is essential: this includes ensuring that we consume the recommended daily dietary intake of calcium. (See the tables at the end for recommended intakes and foods high in calcium.) Dairy foods like milk, cheese and yoghurt are particularly important, because they contain both a high level of calcium and a high level of lactose (milk sugar), which increases the efficiency of calcium uptake. Try low-fat dairy foods if weight or heart disease is a concern – these often contain more absorbable calcium than do whole milk products. Tinned salmon and sardines (with edible bones) also contain high levels of absorbable calcium. Excessively thin girls and women appear to have a higher risk of developing osteoporosis, possibly due to a suppressive effect on the production of oestrogen. In addition, recent research suggests that people with more fat tend to produce more of a hormone called amylin, which has been shown to make osteoblasts grow more quickly and to 'switch off' osteoclasts. Exercise Scientists believe that exercise stimulates osteoblasts to be more active, increasing bone production and reshaping bones so that they have greatest strength where it is needed most. Almost any kind of exercise will help, but the most effective are those that are performed against the force of gravity (called weight-bearing exercises). These include jogging, walking, skipping, dancing, tennis, football, netball and other ball sports. An active lifestyle should begin as early as possible in life: studies have shown that active children have a 24 per cent higher peak bone mass than non-active children. Excessive exercise may also be risky, since it may lead to a reduced production of oestrogen with subsequent negative effects on bone formation. Women whose oestrogen levels have fallen as a result of excessive exercise are sometimes given hormone replacement therapy (Box 2). Other lifestyle issues Smoking and excessive amounts of alcohol are both thought to contribute to the risk of osteoporosis, possibly by inhibiting the actions of hormones that aid calcium absorption. Smokers also tend to have a thinner build and reach menopause earlier. A family matter? Scientists remain uncertain as to why some people are more susceptible to osteoporosis than others. For example, there may be hereditary factors involved: susceptibility increases in people with a family history of osteoporosis. Australian scientists are involved in research to track down genes that may contribute to the treatment or prevention of the disease. Recommended daily allowances of calcium
Source: National Health and Medical Research Council Some foods with a high calcium content
Source: Health Promotions Centre, Department of Community Medicine, Westmead Hospital, NSW Related site
Hormone replacement therapy has been shown to protect against post-menopausal bone loss. There is also evidence that its use is associated with reduced fracture rates throughout the skeleton. In addition, some scientists believe that hormone replacement therapy may have a protective effect against heart disease and stroke. It can also reduce menopause-related symptoms such as hot flushes, mood swings and insomnia. Are there risks? When taken alone, oestrogen is believed to increase the risk of cancer to the lining of the uterus. In recent years, oestrogen has been combined with progestogen in hormone replacement therapy to eliminate this risk. Some studies have suggested that women taking hormone replacement therapy for more than 10 years have a slightly increased risk of breast cancer. Further ongoing research will help clarify the full extent of this risk. The decision to embark on hormone replacement therapy is often a difficult one. Many medical professionals suggest that women who are undecided about taking the treatment should have their bone density measured. This can be done non-invasively using what is called dual energy x-ray absorptiometry and will give some indication of the risk of developing osteoporosis in the future in the absence of oestrogen replacement. Related site
New Scientist 5 April 2008, page 12 To strengthen bones, suck out the marrow (by Colin Barras) Describes a method of healing broken or fractured bones by removing bone marrow.
13 December 2003, page 4 Furore over HRT Looks at research into the risks associated with HRT.
8 August 2003 Long-term HRT doubles breast cancer risk (by Shaoni Bhattacharya) Questions the benefit of long-term hormone replacement therapy.
9 July 2002 New data halts largest HRT trial (by Sylvia Pagán Westphal) Data show that the risks of long term HRT outweigh the benefits.
12 January 2002, page 14 Best catch 'em young...but it's never too late to build up fragile bones (by Alison Motluk) Describes the importance of exercise to bone-building in children and a new drug that can reverse bone loss in older people.
6 May 2000, page 20 Bone relief (by Nell Boyce) Describes two new ways of targeting bone-destroying cells.
28 August 1999, page 11 Body builder (by Robert Adler) Researchers have discovered how parathyroid hormone rebuilds bone.
Inside Science (No. 110), 23 May 1998 Universal body builder (by Patricia Davis) The universal body builder, collagen, is an important protein in bone.
Inside Science (No. 104), 18 October 1997 Food, glorious food (by Gail Vines) Evidence is growing that eating 'protective' foods can actively prevent some diseases – including osteoporosis.
Newsline Issue 34, Autumn 2005, pages 16-17 Bones at risk (by Nina Morgan) Looks at the use of data mining to help prevent osteoporosis.
Scientific American March 2003, page 46 Restoring aging bones (by Clifford J. Rosen) Looks at how the body builds and loses bone and how this information can be used to prevent and treat osteoporosis.
What is osteoporosis? (Osteoporosis Australia)
Provides an introduction to osteoporosis including links to risk factors, diagnosis and the prevention of osteoporosis and fractures.
Australian Broadcasting Corporation (transcripts)
Diseases and Conditions – Osteoporosis (Mayo Clinic, USA)
This is also a good introduction to osteoporosis. Covers causes, prevention and treatment.
The prevention and management of osteoporosis (Medical Journal of Australia)
Presents various aspects of osteoporosis. Of particular interest, What is osteoporosis? and What is the magnitude of the problem in Australia?
Osteoporosis Sydney Support Group
Contains a brief explanation of osteoporosis, including recommended daily intake of calcium.
Living dangerously (The Chemistry Societies Network, UK) A more detailed look at the causes of and treatments for osteoporosis.
ASBMR
bone curriculum (American Society for Bone and Mineral
Research, USA)
Osteoporosis (All ScienceDen.com, USA)
Provides background information on normal bone development and factors involved in osteoporosis and other bone diseases.
hormone. A substance produced in one part of the body and carried by the blood to another part of the body where it causes a response (eg, insulin, produced by the pancreas, that promotes the uptake of glucose by body cells). For more information see The hormones of the human (Kimball's Biology Pages, USA) and The hormones (Center for Bioenvironmental Research, Tulane and Xavier Universities, USA). oestrogen. A female sex hormone secreted by the ovaries. Turner syndrome. A condition affecting females who have only one X chromosome instead of the usual two. Ovaries do not develop normally in females with Turner syndrome. More information can be found at Turner’s Syndrome Society of the United States.
External sites are not endorsed by the Australian Academy of Science. Posted August 1998. The Australian Foundation for Science is also a supporter of Nova. This topic is sponsored by Milk Marketing (NSW).
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