Why are most people in industrialized societies so tired? The reason lies in an increasing discrepancy between our body clocks' internal time and the social demands on work/school days (social jetlag). Because we predominately work inside, our body clocks have become later over the years while work times have stayed approximately the same.Body clocks use the light-dark cycle to synchronize to the 24-hr day, while society manipulates social time (e.g., time zones and daylight saving time) ignoring the internal time of an individual. The signal to fall asleep is predominantly controlled by the body clock, whereas wake-up on workdays is enforced by the social clock. As a consequence, close to 80% of the population uses alarm clocks on workdays. The more "social jetlag" people suffer from, the more likely they are to smoke, drink alcohol, and consume caffeine, and the odds are higher that they belong to the overweight/obese portion of the population.
Current Biology, 10 May 2012 10.1016/j.cub.2012.03.038