Osteoporosis

Osteoporosis is a disease which affects the skeleton and is characterised by low bone mass, deterioration of bone tissue and a consequent increase in bone fragility and susceptibility to fracture. It is often referred to as the 'silent disease' as it is commonly asymptomatic (displaying no symptoms), with many people unaware they suffer from it until they sustain a fracture.

Causes

Osteoporosis is caused by an imbalance in the body’s bone remodelling process. The bone in the body is constantly being broken down, reabsorbed and replaced by the formation of new bone. The cells that break down the bone are referred to as osteoclasts and the cells responsible for bone formation are osteoblasts. From the time of birth until mid to late 20s, the amount of bone formed exceeds that which is lost. In mid to late 20s a person reaches their peak bone mass, the maximum density achieved by their bones (1). From when a person reaches their peak bone mass to around age 35, bone formation and bone loss are in equilibrium. However, after the age of 35 bone reabsorption is greater than bone formation, resulting in a gradual loss of bone. This bone loss can eventually lead to osteoporosis in later life.

Risk factors

A number of risk factors are associated with osteoporosis, the most notable being gender. Women are at much greater risk of osteoporosis than men for several reasons. First, they generally have thinner, lighter bones than men and second, women experience an accelerated rate of bone loss following menopause due to a fall in the production of the female sex hormone oestrogen, which is thought to play a significant role in slowing down the process of bone reabsorption. Women are also at an increased risk because, on average, they live longer than men.

Other risk factors for osteoporosis include:

• slight or slender build
• Caucasian or Asian background
• family history of osteoporosis
• sedentary lifestyle
• small adult peak bone mass
• low calcium intake
• early or premature menopause
• irregular menstrual periods
• smoking
• the excess consumption of protein, alcohol, fibre, caffeine or salt
• long term use of medications that impede calcium absorption (2).

Some facts and figures

Statistical information on Australian osteoporosis rates are somewhat limited as there is no national screening program for its prevention (as there is for conditions like breast and cervical cancer). Currently, much of the statistical data is based on the Dubbo Epidemiology Study in Australia. This epidemiological study involves more than 2 000 men and women over the age of 60 living in the Dubbo area in New South Wales. Beginning in 1989, the study is monitoring the stability, strength and bone density of the participants. Other factors such as family background, medications and lifestyle are also being investigated (3).

Results from the Dubbo Epidemiology Study in Australia suggest that:

• 60% of women and 30% of men will suffer from an osteoporotic fracture after       the age of 60 years.
• 20% of people who suffer from a hip fracture die within 12 months and 26%       remain in nursing homes for the rest of their lives (4).

Another epidemiological study, the Geelong Osteoporosis Study, is investigating age, sex and site-specific fracture rates. Results from this study predict that:

• There will be a 25% increase in the total number of fractures per year by 2006.
• There will be a fourfold increase in the number of hip fractures in Australian       women by 2051 (from 11 300 in 1996 to 44 700 in 2051) (5).

Osteoporosis Australia explain that:

• The number of fractures are increasing at a rate of 4% per annum.
• Every 8.1 minutes in Australia someone is admitted to hospital with a fracture (by 2021 this will become every 3.7 minutes)
• By 2020, 1 in 3 Australian hospital beds will be occupied by women with       fractures.
• More than half of all spinal fractures do not come to medical attention.
• It is estimated that the cost of osteoporosis to the Australian health care       system was 1.9 billion in 2000-1. This does not take into account personal and       indirect costs of the loss of independence and mobility (conservatively       estimated at $5.57 billion in 2000-1) (6).

Prevention

There are a number of steps that people can take at different stages in their lives, to prevent osteoporosis. These include achieving an adequate peak bone mass in early adulthood, maintaining a diet rich in calcium, and undertaking weight-bearing exercise throughout life.

It is important that young people achieve an adequate peak bone mass. Having a good bone mass at this stage means that you can afford to lose more bone mass throughout life. Although peak bone mass is determined largely by genetic makeup it is also influenced by nutrition, exercise and lifestyle factors such as smoking and alcohol use. To achieve an adequate peak bone mass young people need to include enough calcium in their diet, get sufficient weight-bearing exercise and limit smoking and drinking alcohol.

Maintaining a diet rich in calcium is important in the prevention of osteoporosis as calcium plays a vital role in bone development. Because the body is unable to produce calcium, it must be obtained through dietary intake. The recommended daily intake (RDI) of calcium differs for men and women and for people of different ages (see table).

Recommended Daily Intake of Calcium (7).

	Age	Calcium(mg)
Boys	9-11	1000
	12-13	1300
	14-18	1300
Girls	9-11	1000
	12-13	1300
	14-18	1300
Men	19-70	1000
	>70	1300
Women	19-50	1000
	51-70	1300
	>70	1300
Pregnant	14-18	1300
	19-50	1000
Lactating	14-18	1300
	19-50	1000

The best dietary sources of calcium are dairy foods (in particular milk, yoghurt and cheese). Non-dairy sources include: canned fish with bones such as salmon and sardines; dried fruit like figs; green leafy vegetables such as Chinese greens and spinach; almonds and whole seeds (unhulled sesame seeds), and oranges. Soy products with added calcium are also a useful source of calcium in a non-dairy diet.

The following dietary sources all provide approximately 300mg of calcium:

• 250ml regular, reduced fat or skim milk
• 200ml tub yogurt
• 35g cheddar cheese
• 250ml soy milk with added calcium
• 100g canned salmon/sardines
• 6 oranges
• 1 kg broccoli
• 20 slices of wholemeal bread (8).

The amount of calcium that is absorbed through dietary intake depends on the presence of other essential nutrients, in particular Vitamin D. Vitamin D is manufactured in the skin in response to sunlight exposure. Previously it was assumed that most Australians would receive enough sunlight exposure to meet their Vitamin D requirements. However, people lifestyle's mean that they are now less likely to spend time in the sun (particularly during the winter months) and so may be at risk of Vitamin D deficiency. People particularly at risk of Vitamin D deficiency are nursing home residents and people whose clothing covers most of their body (Muslim women). Vitamin D is also present in some foods including full cream milk products, egg yolk, butter and oily fish.

Despite a number of advertising campaigns encouraging women to consume calcium rich foods such as dairy products, a 2002 study found that 76% of women aged 20-54 years had intakes of calcium below the recommended daily intake (RDI) (9). 

Exercise is also important in the prevention of osteoporosis. Weight-bearing exercise (activity which is carried out with both feet on the ground) has been shown to increase bone formation. Weight-bearing exercise includes activities such as jogging, walking and sports like tennis, netball and basketball. Exercise also increases muscle tone, strength, co-ordination, agility and flexibility which can all help prevent falls.

Ideally, an exercise regime should include a combination of weight-bearing exercise, aerobic exercise (exercise which stimulates the heart and lungs like swimming and cycling), flexibility exercise (eg. yoga) and strengthening exercise (eg. weight training). Activities involving more than one type of exercise such as brisk walking, which is both weight-bearing and aerobic, are ideal.

References

This student factsheet is one of a series produced by Women's Health Queensland Wide. They have been developed in response to students' most frequently asked question and reflect a range of topics examined by high school and tertiary students. It has been reviewed by our Editorial Committee. This factsheet is designed for student assignment purposes and, therefore, may not be an appropriate source of information for personal use.

For further information sources on this topic see our "Internet resources for assignments" page

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Last Modified: November 7, 2007