Hyperactivity and anorexia nervosa: behavioural and biological perspective.
Kohl M, et al.
Encephale. 2004 Sep-Oct;30(5):492-9.
Anorexia nervosa is an eating disorder defined by a symptomatic triad, anorexia, emaciation and amenorrhoea. This disease mainly affects young women. Besides these three symptoms, hyperactivity is often associated with anorexia nervosa. Hyperactivity can be considered as a strategy to lose weight, but studies on animal models have shown that it could be explained by more complicated mechanisms. Hyperactivity is defined by an excess of physical activity, which can induce social, professional and family consequences. Hyperactivity can take different forms, most striking is the restless one. Patients with anorexia nervosa are not all hyperactive. Brewerton et al. have compared patients with anorexia nervosa and hyperactivity to patients without hyperactivity. Hyperactive patients are more dissatisfied by their body image, they use less means of purging (laxatives, vomiting), and they start starving earlier than patients without hyperactivity. Many factors can promote the emergence and maintenance of hyperactivity, especially social and cultural requirements, sports environment, family influences. Various models can explain the links between excessive exercise and anorexia nervosa. Epling and Pierce have exposed a behavioural model which shows how hyperactivity can lead to starvation, creating a self-maintained cycle. Eisler and Le Grande have described four models to explain the links between hyperactivity and anorexia nervosa. First, excessive exercise can be considered as a symptom of anorexia nervosa. It can also promote the development of eating disorders. Anorexia nervosa and hyperactivity can be a manifestation of an other psychiatric disorder. At least, hyperactivity can be a variant of anorexia nervosa, which has the same effects, as weight loss. Hyperactivity can also be considered as a kind of obsessive compulsive disorder. Hyperactivity and obsessive compulsive disorders actually share some clinical and neurochemical characteristics. An other model consists in comparing excessive exercise in anorexia nervosa to an addictive behaviour. Self-starvation exacerbated by hyperactivity can be considered as an addiction to endogenous opioid. Few studies are carried out in order to estimate the prevalence of high level exercise in the eating disorders. Davis et al. have achieved a prevalence study. The results indicate that a large majority of patients with anorexia nervosa (80,8%) were exercising excessively during an acute phase of the disorder. Research on animals, specially on rats, brings us an interesting model explaining interactions between anorexia nervosa and hyperactivity. With animal models, we have noticed that, when rats with access to a running wheel, are restricted in their food intake, they become excessively active, and paradoxically reduce food consumption. Many searchers have tried to explain this phenomenon. Morse et al. have pointed from animal models that the level of hyperactivity was linked to the severity of food restriction. This result can be explained by a failure of a part of the brain involved in rest and activity regulation. Animal research brings us explanations about the effects of starvation on the endocrine system and the neurotransmitters. Broocks et al. have shown that corticosterone concentration in plasma was synergistically increased by semi starvation and exercise, and the reduction of triiodothyronine by semi starvation was significantly greater in the running wheel group. An other study of Broocks et al. has revealed an increased hypothalamic serotonin metabolism with the combined effect of hyperactivity and food restriction. Tryptophan, an amid acid involved in serotonin synthesis, can also play a role in the maintenance of anorexia nervosa. In starvation conditions, opioid releasing caused by physical exercise would decrease food intake. Exner’s study and Adan’s one have shown that leptin would be involved in semi starvation induced hyperactivity mechanisms. In spite of animal models can not be entirely generalized to human, they are useful to try to explain biological supports of hyperactivity. Hyperactivity is not only a strategy to lose weight, but also a specific symptom which completes the clinical triad. Animal studies have led to promising results; we might use medicine, such as serotonin reuptake inhibitors or opioid antagonists in the treatment of hyperactivity in anorexia nervosa.
Source: Service du Professeur Reynaud, Hôpital Paul Brousse, 12, avenue P.-V. Couturier, 94804 Villejuif, France.
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