Daily or “circadian” rhythms including the sleep wake cycle, and rhythms in hormone release are controlled by a molecular clock that is present in every cell of the human body. This human clock has its own inbuilt, default rhythm of almost exactly 24 hours that allows it to stay finely tuned to the daily cycle generated by the rotation of Earth. This beautiful symmetry between the human clock and the daily cycle of Earth’s rotation is disrupted by exposure to artificial light cycles, and by irregular meal, work and sleep times. This mismatch between the natural circadian rhythms of our bodies and the environment is called “circadian desynchrony.”

“Electric light allowed humans to override an ancient synchronization between the rhythm of the human clock and the environment, and over the last century, daily rhythms in meal, sleep and working times have gradually disappeared from our lives … The human clock struggles to remain tuned to our highly irregular lifestyles, and I believe that this causes metabolic and other health problems, and makes us more likely to become obese." - Dr. Cathy Wyse (Chronobiology research group, University of Aberdeen)