Chronobiology, Sleep Disturbances and Food Intake Disorders



Rok publikování 2014
Druh Kapitola v knize
Fakulta / Pracoviště MU

Lékařská fakulta

Přiložené soubory
Popis Circadian rhythmicity is an intrinsic property of various body cells and tissues, and is driven by so-called clock control genes and their products. Variation in clock control genes have been linked to various components of metabolic syndrome. Experimental animals with knock-out of those genes show food intake disorders as well as variety of common diseases. At the systemic level, circadian rhythmicity is synchronized by master clock in hypothalamic suprachiasmatic nucleus (SCN). SCN responds to external stimuli (zeitgebers) by promoting the secretion of hormone melatonin from pineal gland , regulating hypothalamus-hypophysis-adrenal glands axis and influencing the body temperature. The principal zeitgeber is the light-dark cycle, however, SCN settings is also influenced by other stimuli such as nutrition intake during the day. The desynchronization of internal SCN settings and dai ly activity (circadian misalignment) can lead into potentially adverse consequences for metabolism. Circadian misalignment frequently occurs as a result of shift work or jet lag. Social jet lag refers to shifts in circadian activity, mostly between working days and weekends. People with preference for evening activity (evening chronotype) are at higher risk of circadian misalignment because of repeated phase shifts twice a week; moreover, reduced sleep time also lead into preference for unhealthy food composition and weight gain . Expression of many endogenous substances that influence appetite and food intake shows circadian rhythmicity and can be altered by circadian misalignment. Besides melatonin, these substances include glucocorticoids, insulin, leptin, ghrelin, or neuropeptides as orexins/hypocretins, pro-opiomelanocortin, CART or neuropeptide Y. Some of those substances have orexigenic and some have anorexigenic effects. Circadian misalignment may result in increased leptin resistance and predominance of orexigenic pathways . Obstructive sleep apnea (OSA) is in complex relationship with food intake and obesity. While overweight is a predisposing factor of sleep apnea, sleep fragmentation and restriction can adversely influence appetite. Together with sympathetic hyperactivation resulting from intermittent hypoxia, this can lead into vicious circle resulting in metabolic syndrome . Night eating can also be considered a dysfunction of circadian rhythmicity. Clinical entity called Night eating syndrome (NES) has been recently accepted for inclusion in the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders. Despite its validity and usefulness are discussed, NES can lead into adverse metabolic consequences. Seasonal affective disorder (SAD) is a disorder of bipolar/depressive pattern with significant chronobiological component. It typically manifests during the winter and is associated with changes in melatonin release. Weight gain and/or binge eating typically accompany the clinical picture of SAD. The knowledge of circadian regulation of appetite has considerable therapeutic implications in obesitology. Light hygiene and bright light exposition in the morning both have a potential to prevent circadian misalignment and weight gain. Regular intake of food without caloric restriction has been shown to reduce body weight in laboratory animals. Melatonin also showed weight-lowering effect in several animal studies, although the data in humans are insufficient. Melatonin and its analogues thus have an anti-obesitogenic potential that has to be confirmed in clinical studies

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