Social jetlag, circadian disruption, and cardiometabolic disease risk

The sun rises and sets over the earth in a predictable pattern. This pattern has existed for billions of years and has influenced the behavior of all living things. Behavioral rhythms have aligned with these light-dark rhythms and conferred an evolutionary advantage. Humans have adapted to the light-dark cycle so that activity occurs during the day and rest occurs during the night. Increased visibility afforded by daylight optimizes foraging and safety while being active. Reduced visibility during the night optimizes sleeping and fasting. Daily rhythms, such as light-dark, are known as circadian rhythms from the Latin words “circa,” for about, and “dias,” for a day. Physiological processes rely on predictable circadian rhythms. These processes include sleeping and waking, cardiac function, such as heart rate and blood pressure, and metabolic processes, such as glucose, lipid, and energy metabolism. Disrupting circadian rhythms can profoundly impact cardiometabolic health and well-being. Poor cardiometabolic health can also disrupt the circadian system. This chapter will briefly introduce the cardiometabolic syndrome, the circadian system, circadian disruption, and social jetlag as a form of circadian disruption.