Even those with only slightly altered sleep schedules pay a price. According to Roenneberg, a third of the population in his database suffers from two or more hours of social jet lag, and 69 percent reported at least one hour of social jet lag. That might be enough, studies suggest, to increase the risk of becoming overweight or obese by 33 percent.
"It took me about 50 years of my life to understand what an alarm clock means," Roenneberg concludes. "It means that you haven’t slept your biological sleep to the end."