After reviewing the scientific evidence in 2015, the American Academy of Sleep Medicine together with the Sleep Research Society now recommends that "adults should sleep 7 or more hours per night on a regular basis to promote optimal health". Astonishingly, according to nationally representative surveys 35 to 40 percent of Americans report sleeping less than 7 hours on weekday nights, and 15 percent report sleeping less than 6 hours.
There are several plausible explanations for this population "sleep debt", that is the discrepancy between the biological need for sleep and the amount of sleep people actually get. In two seminal studies published in 2003, subjects were chronically sleep deprived over a period of 14 consecutive days by restricting the opportunity for sleep to 4 to 7 hours per 24 hours.
While objectively measured cognitive performance decreased steadily with every study day -- reaching levels observed in people who did not sleep at all for up to two nights -- subjective reports of sleepiness leveled off quickly after an initial short increase. Thus, humans seem to get used to chronic sleep restriction fast. The sleepiness that felt overwhelming after a night or two of sleep restriction quickly feels normal.
We don't realize that our cognitive performance is still impaired and how much better we could feel and perform if we only got more sleep. It is no wonder that patients with obstructive sleep apnea, a sleep disorder that reduces sleep time through sleep fragmentation, often report feeling "reborn" after the first night of therapy. Caffeine will keep us going during the day, but is obviously no replacement for sleep.
While sleep was considered an "anemia of the brain" and thus a passive state a century ago, we now know that it is quite the opposite. Sleep is a very active process that serves vital biological functions. The brain is cleared of metabolic waste products during sleep, and we gain important new insights.
According to Tononi and Cirelli "sleep is the price we pay for the brain's plasticity - its ability to modify its wiring in response to experience". We thus consolidate new experiences believed to be important, but also make room for new ones. Epidemiologic studies show that chronic short sleep is associated with a host of negative health outcomes like cardiovascular disease and diabetes.
Finally, sleep restriction, like alcohol, increases the risk for errors and accidents; fatigue from sleep loss is considered the primary cause of 20 to 25 percent of traffic accidents, with ca. 1,000 fatalities attributable to falling asleep behind the wheel each year. That's why sleep is a biological imperative, and sleep restriction affects us and our health in many ways. Yet, large parts of the population perceive sleep as a nuisance, unproductive, and as a flexible commodity that can be traded for other activities considered more pressing or of greater value.
Based on the nationally representative American Time Use Survey, we found that the waking activity most likely traded for sleep was working, followed by traveling, the bulk of which is commuting to and from work. This was true across practically all sociodemographic strata. Confronted with these results, we were looking for possible behavioral interventions to increase sleep time. As work time is often out of an individual's control, we concentrated our analyses on activities performed in the 2 hours before going to bed and the 2 hours after waking up, as we thought activities in these periods could most likely be "traded" for more sleep.
One important finding of this analysis was that almost 50 percent of the time in the 2 hours pre bed is spent watching TV. Interestingly, those who worked long hours got up significantly earlier in the morning compared to those who worked short hours or not at all. One would expect that early risers also retire earlier at night to still log enough hours of sleep. Surprisingly though, the times when people went to bed did not depend on work duration or morning rise time at all.
Those who did not have to work at all watched on average 61.1 minutes TV in the two hours pre bed, while those who worked longer than 8 hours still watched 50.7 minutes. This suggests that long workers who have to rise early could increase their sleep time by turning off the TV and retiring earlier at night.
However, while everybody has access to alarm clocks that reliably end the sleep period in the morning, an evening equivalent -- that is an alarm clock that tell us when to go to bed -- has not been widely available until the recent introduction of Apple's Bedtime feature with iOS 10.
The feature allows you to set evening alarm times that will remind you when it is time to go to bed in order to meet your individual sleep need. Although it is unclear how many Apple users will adopt this feature, and of those who do, how many will actually adhere to the alarm, it will at least raise awareness of the importance of retiring early to achieve the recommended minimum 7 hours of sleep each night (acknowledging that some people with late circadian preference, so called owls, cannot fall asleep early).
Right now, it is quite the opposite. Meteorologists and talk show hosts tell us to stay up and suffer through yet another commercial break to finally learn what the weather will be like tomorrow or whether Matt Damon will make the interview with Jimmy Kimmel this time.
At last year's annual SLEEP meeting, I advocated for a national TV campaign (similar to those seen for smoking) that reminds people of the importance of sufficient sleep and asks them to turn off the TV and go to bed early to meet their individual sleep need. For obvious reasons, this is not very likely to happen. Apple's Bedtime feature seems a first step in the right direction, but only the future will show whether people will adopt and profit from it.