The autonomic nervous system (ANS) and the immune system are deeply interrelated. The ANS regulates both innate and adaptive immunity through the sympathetic and parasympathetic branches, and an imbalance in this system can determine an altered inflammatory response as typically observed in chronic conditions such as systemic autoimmune diseases. Rheumatoid arthritis, systemic lupus erythematosus, and systemic sclerosis all show a dysfunction of the ANS that is mutually related to the increase in inflammation and cardiovascular risk. Moreover, an interaction between ANS and the gut microbiota has direct effects on inflammation homeostasis. Recently vagal stimulation techniques have emerged as an unprecedented possibility to reduce ANS dysfunction, especially in chronic diseases characterized by pain and a decreased quality of life as well as in chronic inflammation.

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Obesity and sleep disturbances are common conditions in modern societies and accumulating evidence support a close bidirectional causal relationship between these two conditions. Indeed, from one side sleep loss seems to affect energy intake and expenditure through its direct effects on hormone-mediated sensations of satiety and hunger and through the influence on hedonic and psychological aspects of food consumption. Sleep deprived patients have been shown to experiment excessive daytime sleepiness, fatigue, and tiredness that, in a vicious circle, enhances physical inactivity and weight gain. On the other side, obesity is a well-known risk factor for several sleep disorders. This narrative review will discuss the main pathophysiological mechanisms that link sleep loss to obesity and metabolic syndrome with particular attention to the three most common sleep disorders (insomnia, obstructive sleep apnoea syndrome, restless leg syndrome).