Published by Australian Academy of Science
Pointing the bone at osteoporosis Box 1 | Ensuring a healthy balance at the bone bank

We can all take steps to ensure that we achieve our maximum possible peak bone mass.

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

Girls	up to 7 years 8-11 years 12-15 years 16-18 years	800 mg 900 mg 1000 mg 800 mg
Women aged 19-54 years Menopausal women and women over 54 years Pregnant women Breastfeeding women		800-1000 mg 1000 mg 1100 mg 1200 mg
Boys	Up to 11 years 12-15 years 16-18 years	800 mg 1200 mg 1000 mg
Men 19 years and over		800 mg

Source: National Health and Medical Research Council

Some foods with a high calcium content

Product	Serve	Calcium (milligrams)
Milk and milk products Whole milk Skim milk Modified, low fat milk (eg, Shape, Fitness) Modified, reduced fat milk (eg, Hi Lo, Rev) Yoghurt – natural Cheese – Swiss – Cheddar – Mozzarella, Edam	250 ml (1 cup) 250 ml (1 cup) 250 ml (1 cup) 250 ml (1 cup) 200 g (1 carton) 25 g (1 slice) 25 g (1 slice) 25 g (1 slice)	290 310 410 350 285 240 215 180
Soy products Fortified soy milk (eg, So-Good) Tofu	250 ml (1 cup) 200 g	290 240
Tinned fish Sardines – tinned Salmon – tinned with bones	100 g 100 g	350 190
Dishes Quiche Lorraine Cheese souffle Lasagna/cannelloni Moussaka Tahini paste Pizza Cheeseburger Fish in batter	1 slice 100 g 200 g 200 g 25 g (1 tablespoon) ½ medium 1 100 g	390 240 130 180 230 350 100 75

Source: Health Promotions Centre, Department of Community Medicine, Westmead Hospital, NSW

Related site

• What interventions are effective in preventing osteoporosis and osteoporotic fractures? (Medical Journal of Australia)

Other boxes

Box 2. Hormone replacement therapy