Osteoporosis

Overview of Osteoporosis in Eating Disorders

Osteoporosis is a breakdown of the internal structure of bone which leaves the skeleton fragile and vulnerable to fracture. Although osteoporosis is quite rare in healthy people below the age of 55-60 years, it is a common complication of anorexia nervosa. Bulimia nervosa doesn’t usually lead to osteoporosis unless there is a previous history of anorexia nervosa.

Osteoporosis caused by anorexia nervosa may not be completely reversible, particularly if the illness starts before puberty and continues well into adult life. The longer anorexia nervosa continues and the greater the extent of weight loss, the more fragile the skeleton becomes. Fractures of the spine result in permanent pain, disfigurement and disability. The only effective means of improving bone health and reducing the risk of fracture in anorexia nervosa is to achieve and maintain a healthy weight.

There are two main reasons why anorexia nervosa can cause osteoporosis. First, the illness usually starts during the teenage years when bones are still developing their structure and strength. Malnutrition and low weight slow bone development and growth. Second, if anorexia continues into a person’s 20s and 30s, they start to lose bone prematurely. The worst case scenario is when people develop anorexia nervosa at a younger age (before they are fully grown and developed) and develop a chronic condition. If recovery from anorexia occurs during the teens and early 20s, there is a greater chance of ‘catching up’ and achieving a healthier bone mass.

Causes of Osteoporosis in Eating Disorders

In the early 1980s it was assumed that the main cause of osteoporosis in young women with anorexia nervosa is a deficiency of the sex hormone oestrogen. Oestrogen deficiency is usual in girls/women with anorexia nervosa who do not have periods. In the past, women with anorexia were prescribed oestrogen, usually in the form of the oral contraceptive pill, to help protect their bones. However, research showed that few anorexic women benefited from this treatment. In fact, many continued to lose bone.

We now know that the main cause of osteoporosis in anorexia nervosa is low body weight and malnutrition. Research has shown that when the body is malnourished and weight is too low, there are many hormonal changes which disrupt bone health, in both sexes. The only way to reverse these abnormal hormonal changes is through a healthy diet that leads to weight gain. During and after weight gain, bones begin to strengthen. In girls and women with anorexia nervosa, regular periods are also necessary for a healthy skeleton.

Diagnosis of Osteoporosis in Eating Disorders    

Osteoporosis is usually diagnosed using a procedure called dual energy x-ray absorptiometry (DXA) which measures bone mineral density (BMD) - i.e. the amount of mineral in a given area of bone. The sites of measurement for diagnosis are the lumbar (lower) spine and the hip. A DXA scan provides a comparison of a person’s BMD to normal, healthy values for a male or female of a particular age. It is a painless procedure which involves the person lying on a couch for 5-10 minutes while the scanner moves above the body. Doctors treating individuals with anorexia nervosa usually recommend a DXA scan, especially if body weight has been low for some time.

Treatment of Osteoporosis in Eating Disorders    

Research has shown that the only effective treatment of osteoporosis in anorexia nervosa is weight gain and the maintenance of a healthy weight (i.e. a body mass index between 19 and 25 kg.m-2 . Indeed, weight gain is usually essential to prevent irreversible damage to other organs in the body such as the heart, gut and kidneys as well as the skeleton. The greatest concern about osteoporosis and fracture is in girls who develop anorexia before their periods start, and in boys who should still be growing in height. There is a risk of permanently stunted growth in these individuals.

Treatment with hormones and drugs is not normally advised in people with eating disorders. This is because these treatments are not very effective. If anorexia nervosa develops after periods have already started in girls, or growth is near complete in boys, bone that has been lost may be regained, provided the illness hasn’t continued for more than 2-3 years. The longer the duration of low weight and the lower the weight reached in anorexia nervosa, the greater the risk of irreversible osteoporosis.

Exercise and calcium supplements are often recommended for older people with osteoporosis related to the menopause or older age; however, neither of these treatments is very effective in anorexia nervosa. Exercise aids bone health in children and adults of a healthy weight, but may pose a serious risk to people with anorexia nervosa. Intense or prolonged exercise at a low weight increases the widespread complications of starvation on all organs and should be avoided.

After recovery from anorexia nervosa, carefully prescribed exercise may help to build bone. However, advice should be taken from an eating disorder specialist before starting an exercise regime during recovery from anorexia. Factors such as heart health and BMD need to be considered. Calcium supplements are unlikely to aid bone health when weight is low and may even worsen metabolic complications in people with very low weight.   

Dr. Cathy L Zanker, Reader in Exercise Physiology, Leeds Metropolitan University.     

Useful Links

The National Osteoporosis Society
PO Box 10, Radstock, Bath, BA3 3YB
Helpline: 01761 472721
Office: 01761 471771