The circadian rhythm of sleep occurs in a cyclical 24-h pattern that is adjusted by the influence of several main synchronizers or “zeitgebers”. The most powerful synchronizer is the light–dark alternation, but also, socio-economic factors play a role, such as social and work relationships. Circadian rhythm regulation plays a crucial role in human health. This disruption of circadian rhythm can lead to increased incidence of diseases: diabetes, obesity, cancer, neurodegenerative diseases, increased risk of cardiovascular disease and stroke. Polygenic variations and environmental factors influence the circadian rhythm of each person. This is known as chronotype, which manifests itself as the degree of morning of evening preferences of each individual. There are indications to establish an association between individual chronotype preferences and the behavior of respiratory diseases.
