Living against the clock.

• Position: Obesity Triggers - Circadian desynchrony

When Thomas Edison tested the first light bulb in 1879, he never could have imagined that this invention one day could contribute to a global obesity epidemic. Electric light allows us to work, rest, and play at all hours of the day, and a paper published in Bioessays suggests that this might have serious consequences for our health and for our waistlines.

Daily or circadian rhythms include 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 in-built, default rhythm of almost exactly 24 hours that allows it to stay finely tuned to the daily cycle generated by the rotation of the Earth. This symmetry between the human clock and the daily cycle of the 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," notes Cathy Wyse, working...