Sleep in eating disorders.
Sleep research on eating disorders has addressed two major questions: (1) the effects of chronic starvation in anorexia nervosa and of rapidly fluctuating eating patterns in bulimia nervosa on the sleep regulating processes and (2) the search for a significant neurobiological relationship between eating disorders and major depression. At present, the latter question appears to be resolved, since most of the available evidences clearly underline the notion that eating disorders (such as anorexia and bulimia nervosa) and affective disorders are two distinct entities. Regarding the effects of starvation on sleep regulation, recent research in healthy humans and in animals demonstrates that such a condition results in a fragmentation of sleep and a reduction of slow wave sleep. Although several peptides are supposed to be involved in these regulatory processes (i.e. CCK, orexin, leptin), their mode of action is still poorly understood. In opposite to these experimentally induced sleep disturbances are the findings that the sleep patterns in eating disorder patients per se do not markedly differ from those in healthy subjects. However, when focusing on the so-called restricting anorexics, who maintain their chronic underweight by strictly dieting, the expected effects of malnutrition on sleep can be ascertained. Furthermore, at least partial weight restoration results in a 'deepening' of nocturnal sleep in the anorexic patients. However, our knowledge about the neurobiological systems (as well as their circadian pattern of activity) that transmit the effects of starvation and of weight restoration on sleep is still limited and should be extended to metabolic signals mediating sleep.