In the mid-1800s, the United States was not divided up into four time zones, as it is now. It was divided into 144 time zones, each city setting its clock by the position of the sun overhead. You can imagine why this became a problem when railroads began to criss-cross the country. Who the hell could keep straight what time a train would arrive in Chicago when there were dozens of time zones separating it from New York? As crazy as that system of time may have been, though, it was likely healthier for our bodies. According to an article in The New Yorker, many of us sleep poorly, and have trouble waking up, because we're not actually sleeping when we should be.
"The difference between one’s actual, socially mandated wake-up time and one’s natural, biologically optimal wake-up time is something that Till Roenneberg, a professor of chronobiology at Ludwig-Maximilians University in Munich, calls 'social jetlag,' " explains The New Yorker. "It’s a measurement not of sleep duration but of sleep timing: Are we sleeping in the windows of time that are best for our bodies? According to Roenneberg’s most recent estimates, based on a database of more than sixty-five thousand people, approximately a third of the population suffers from extreme social jetlag—an average difference of over two hours between their natural waking time and their socially obligated one. Sixty-nine per cent suffer from a milder form, of at least one hour."
So we're often not sleeping when we should be. That's bad, right? According to Roenneberg's research, it's very bad. He's correlated every hour of social jetlag with a 33 percent greater chance of obesity, and claims that night shift workers suffer unusually high rates of medical issues due to their sleep schedules. She says social jetlag "could be the most prevalent high-risk behaviour in modern society." And it affects cognition, too--another study showed that med student performance was affected more by when they slept than by how much they slept.
The New Yorker links the concept of social jetlag with another sleep concern called sleep inertia. Sleep inertia refers to that groggy period of waking up in the morning, which actually lasts longer than we think. It can take a couple hours after waking up for sleep inertia to wear off--the prefrontal cortex takes awhile to fully come on line--and memory, decision making, and other functions are impaired during that time. Even if we think we're awake after half an hour, our brain isn't necessarily firing on all cylinders just yet.
It can take a couple hours after waking up for sleep inertia to wear off and memory, decision making, and other functions are impaired during that time.
The good news, according to The New Yorker, is that dealing with social jetlag would likely deal with sleep inertia. Another experiment discovered that adjusting sleep schedules to more natural times saw a dramatic decrease in sleep inertia. Neuroscientist Kenneth Wright sent a group of subjects out on a camping trip, and concluded that displaced melatonin is to blame for our poor morning wakefulness.
"In the days leading up to the trip, he had noted that the subjects’ bodies would begin releasing the sleep hormone melatonin about two hours prior to sleep, around 10:30 P.M," writes The New Yorker. "A decrease in the hormone, on the other hand, took place after wake-up, around 8 A.M. After the camping trip, those patterns had changed significantly. Now the melatonin levels increased around sunset—and decreased just after sunrise, an average of fifty minutes before wake-up time. In other words, not only did the time outside, in the absence of artificial light and alarm clocks, make it easier for people to fall asleep, it made it easier for them to wake up: the subjects’ sleep rhythms would start preparing for wake-up just after sunrise, so that by the time they got up, they were far more awake than they would have otherwise been."
If we all adhered to our natural sleep schedules, we'd probably be far more productive over the course of a day. At the very least, we wouldn't go through the groggy snooze button ritual every morning as we convince ourselves a few more minutes of sleep is going to help us wake up.