The Risk of Osteoporosis in Anorexia Nervosa

While many of the medical complications of anorexia nervosa are reversed by weight restoration, osteoporosis is a very serious one, which may persist even after successful treatment of the eating disorder. Osteoporosis refers to a loss of bone mineral density which is more than 2.5 standard deviations from normal when the patient's bone density is compared with that of a young, healthy reference population. This means that the bone densities of women with osteoporosis are roughly in the lowest 5% for women their age, or that about 95% of women of this age have a greater bone density.

Osteoporosis cannot be diagnosed from a blood test or a normal x-ray. The most commonly used technique for measuring bone density is dual-energy x-ray absorptiometry (DEXA). A DEXA scan takes about 30 minutes to perform, is painless and has a low radiation risk. Treatment providers usually recommend obtaining a DEXA scan in any adult anorectic patient who has more than a two-year history of the illness. Some suggest that a DEXA scan be obtained if the patient has not had menstrual periods for about 12 months.

Diagnosing osteoporosis by DEXA scan in a patient with anorexia nervosa has important treatment and clinical management implications which will be described below. Furthermore, the results provide graphic visual evidence that there is a serious medical problem. It may be effective to show the DEXA results to the patient and advise her that she is progressing toward having the same bone density as an elderly woman. This information may be used for leverage to promote restoration of body weight.

As opposed to the postmenopausal state where there are multiple proven treatments for osteoporosis, including hormones, bisphosphonates, and calcitonin, few therapeutic options are available for the anorectic patient. Hormonal replacement therapy (e.g. estrogen), has recently been proven to be much less effective in anorexia nervosa. Studies in anorexia have demonstrated that oral hormone pills given as either estrogen replacement therapy or oral contraceptives does not preserve or restore bone mass. However, since some data do support a possible benefit, estrogen replacement therapy should not be abandoned; rather it cannot be considered the panacea for osteoporosis.

Similarly, the value of taking calcium, the single most important nutrient for attaining bone mass, is also questionable. Yet, despite the lack of definitive evidence, supplemental daily calcium (1,500 mg/d) and vitamin D (400 IU/d), taken in divided doses with meals, are the standard of care for amenorrheic patients with anorexia nervosa. Other therapeutic options proven to effective in other forms of osteoporosis, including medications known as selective estrogen receptor modulators and bisphosphonates, while not yet the standard of care, may hold promise.

If caught during mid-adolescence, vigorous nutritional rehabilitation, which includes normal and healthy amounts of calories, protein, fats, carbohydrates, vitamins and minerals, has been shown to stem the development of osteoporosis and may in some cases at least partially reverse damage that has been done. Therefore, in light of the lack of proven effective treatments, emphasis must be placed on aggressive multidisciplinary treatments to facilitate early restoration of body weight and return of menses before significant bone loss occurs. This will not only reduce the rate of bone loss but also increase bone mass.

However, it is unwise to conclude that bone density, once lost, will return to pre-illness levels just with weight gain. More than 50% of women and men with anorexia nervosa develop osteoporosis because the maximum bone mass achieved as an adult is the main determinant of future osteoporotic risk. Since anorexia has its greatest incidence in late adolescence and the early twenties, a time in which peak bone mass is normally being attained, these patients will never reach that level of bone density. As a result, the risk of fractures is almost 300% greater in individuals with a history of anorexia nervosa compared with age-matched controls. Even a transient episode of anorexia in youth may permanently impair skeletal integrity.