OSTEOPOROSIS

‘Some people get all the breaks.’ ‘Get well soon’ card

What is osteoporosis?

Osteoporosis is the loss of calcium from bone with consequent fragility and increased risk of fracture. Our bones reach peak strength in our late teens/early twenties. After that it is all down hill. We start to lose bone strength from the age of about 35 and the loss continues throughout life, but becomes more rapid in women after the menopause. From middle age we lose about 1 per cent of our bone mass annually.

The best measure of the thickness and strength of bone is the Bone Mineral Density (BMD) which can be assessed by a particular type of scan – the “Dexa scan”. This gives a so-called  “T-Score”. A T-score of between -1 and -2.5 defines a mild degree of bone weakness known as osteopenia. Any level below – 2.5 defines osteoporosis.

How common is osteoporosis?

Some 3 million people in the UK have osteoporosis.  After the age of 50 about half the population is affected by osteopenia.

And why does it matter?

Any bone in the body may be affected – more important is the risk of the weakened bone breaking after relatively minor trauma. In the UK there are more than 300,000 fragility fractures annually. The commonest and most important fragility fractures are those of the vertebra, the hip and the wrist. These are extremely painful and debilitating and lead to temporary or sometimes permanent disability and dependency. They may be life shortening.  Ten percent will die within a month and about 30 per cent within a year. Hip fractures alone occupy 1.3 million hospital bed days and cost the English economy £1.5 billion annually. Post-menopausal women are particularly susceptible, though men are not immune.

What causes osteoporosis?

Our bones are not inert struts to support our carcasses – they are living structures which continually renew themselves to maintain their functional strength, old bone continuously being replaced by new. Weight-bearing is needed to promote this process. Weightlessness, as in space flight, leads rapidly to loss of bone strength and osteoporosis.

The main causes of osteoporosis are reduction in sex hormone levels (oestrogen and testosterone), lack of calcium and vitamin D and physical inactivity. As men age their blood testosterone levels decline gradually but in women the loss of oestrogen at the menopause is much more sudden and puts women at much greater risk of osteoporosis.

Exercise in the prevention of osteoporosis

Hormone replacement therapy (HRT) does more than prevent hot flushes – it also protects against osteoporosis.

Exercise prevents or delays the onset of osteoporosis by putting a load on the bones and this promotes bone strength. Weight-bearing exercise is the most effective, particularly ‘impact’ exercise like running or skipping. Population studies involving athletes confirm this and indicate that high-impact sports, such as running, squash and weightlifting, lead to an increase in BMD, whereas low-impact sports such as swimming do not.

An early start is important. The more time spent on moderate to vigorous physical activity in adolescence, the greater is bone mass by the age of 25. This is the age at which bone mass peaks and this is a marker of risk of osteoporosis later in life.

For the spine and lower limbs, weight-bearing exercise is what does the business. However, the really important question is whether exercise reduces the risk of osteoporosis-related fractures, particularly of the hip or vertebrae, which can be so devastating for the sufferer. No intervention study has assessed the effect of exercise on the rate of osteoporotic fracture. That is to say, no one has carried out a randomised controlled trial of exercise versus no exercise to show that the exercised group has a lower long-term risk of fracture – such a trial would be extremely difficult to perform. However, observational epidemiological studies have indicated a strong protective effect. A study of 3,262 healthy men (mean age 44 years) followed for 21 years found that intense physical activity at the start of the study was associated with a reduced incidence of hip fracture, the risk being just 38 per cent of the risk for the non-exercisers. Another study from the USA reported that women who had a high frequency of participation in outdoor sports had just 30 per cent the chance of suffering a hip fracture compared with those with a low-frequency of participation. A similar risk reduction has been reported in studies from Britain and Hong Kong. As one reviewer wrote: ‘physical inactivity is currently proffered as the most salient explanatory factor for the increasingly high hip fracture rates reported by developing countries, as well as many first-world countries’.

A neat way of showing the effect of exercise on BMD is to examine the effects on different limbs. Squash players from Finland showed a 15.6 per cent higher BMD at the proximal humerus (upper arm) of the racquet hand than the inactive arm.

Cochrane in 2011 reviewed the evidence for the role of exercise in preventing osteoporosis and related fractures in post-menopausal women. They found an important reduction in osteoporosis from exercise programmes – resistance strength training being most effective in protecting the hip and combination exercise best for the spine. For the women studied, the overall fracture rate was 11 per 100 in those who did not exercise compared to 7 per 100 in those who did – a saving of 4 fractures for every 100 exercisers.

One difficulty in interpreting this evidence is the confounding fact that regular exercise lessens the risk of falling, so that fewer fractures may be the result of falling less rather than having stronger bones. Probably both are true.

Exercise in the treatment of osteoporosis

A definitive assessment of the effectiveness of exercise in treating osteoporosis was published in 2012. After analysis of 74 trials, the authors concluded that aerobic exercise and weight training do increase bone mass, or at the very least reduce the rate of bone loss, in osteoporotic (mostly post-menopausal) women. They found that the lower the BMD, the more effective was the exercise as a treatment. ‘The best improvements seem to be achieved through strength training of high-loading intensities with 3 sessions per week and 2–3 sets per session. Although significant effects can be observed after 4 or 6 months in some locations of the body, the efficacy of the training programme is greater when it extends for at least 1 year’.

The National Osteoporosis Society produces a 60-page booklet of exercise advice for osteoporosis prevention and treatment (https://www.nos.org.uk/health-professionals/~/document.doc?id=770).