The circadian system, sleep, and the health/disease balance: a conceptual review

The field of circadian medicine is a recent addition to chronobiology and sleep research efforts. It represents a logical step arising from the increasing insights into the circadian system and its interactions with life in urbanised societies; applying these insights to the health/disease balance at home and in the medical practice (outpatient) and clinic (inpatient). Despite its fast expansion and proliferating research efforts, circadian medicine lacks a formal framework to categorise the many observations describing interactions among the circadian system, sleep, and the health/disease balance. A good framework allows us to categorise observations and then assign them to one or more components with hypothesised interactions. Such assignments can lead to experiments that document causal (rather than correlational) relationships and move from describing observations to discovering mechanisms. This review details such a proposed formal framework for circadian medicine and will hopefully trigger discussion among our colleagues, so that the framework can be improved and expanded. As the basis of the framework for circadian medicine, we define circadian health and how it links to general health. We then define interactions among the circadian system, sleep, and the health/disease balance and put the framework into the context of the literature with examples from six domains of health/disease balance: fertility, cancer, immune system, mental health, cardiovascular, and metabolism.

Automated summary

Circadian medicine, a recent addition to chronobiology and sleep research, applies the insights into circadian system and its interactions to the health/disease balance in medical practices. However, there is currently a lack of a formal framework to categorize and describe the interactions among circadian system, sleep, and health/disease balance. This review proposes a formal framework for circadian medicine and provides examples from various health/disease domains.