More than 30 percent of adult Americans, about 60 million people, complain of difficulty sleeping. For about a quarter of these individuals, treatment begins with medication. This tells us two things. Sleep is a big problem and a big business.
So how does one of the most basic biological functions become so disordered? After all, what could be more natural than sleep?
The first thing you notice when digging into what we know about sleep is how little we understand. The function of sleep, a state that occupies one-third of our lives, remains unclear. Why is sleep necessary for our survival? Why do we dream?
Sure, we have made some connections by observing what happens to people who are sleep-deprived or perform shift work. Clearly, physical and cognitive function take a hit. Medical interns working on the night shift are twice as likely as others to misinterpret hospital test records that could endanger their patients. The Exxon Valdez oil spill and the Three Mile Island and Chernobyl nuclear power plant accidents were attributed in part to the consequences of compromised night shift workers. We know memory and learning are impaired. Protein synthesis that produces the building blocks needed for cell growth and repair is markedly diminished. But theses are crude observations, not understanding.
The second thing you realize, and this boggles the mind, is that almost everything we do know about human sleep has been learned in the last 50 years. Unfortunately, like the first beliefs in any discipline, many of the early theories about our sleep were wrong.
Until recently, humans were thought to be different from all other animals in having sleep that is consolidated into one continuous nocturnal episode. This notion of uniquely human sleep held sway until the early 1990s when Thomas Wehr, a sleep researcher at NIMH inadvertently stumbled on something that changed everything, or should have.
Wehr selected healthy untroubled sleepers who were accustomed to 16-17 hour days and seven to eight hours of sleep, a routine that many of us live by or envy because we get less sleep. He exposed them to 10 hours of light and 14 hours of dark per day and watched what happened to their sleep. This ratio of light to dark (10:14) mimics the natural light of a typical winter day in a temperate climate. Initially, they slept for 11 hours per night, suggesting a chronic sleep deficit, and then settled into an average of 8.9 hours each night. By the fourth week Wehr saw something that wasn't supposed to happen in humans. They all developed a sleep pattern characterized by two sleep sessions. Subjects tended to lie awake for one to two hours and then fall quickly asleep. After about four hours of solid sleep, they would awaken and spend one to two hours in a state of quiet wakefulness before a second four-hour sleep period.
This bimodal sleep has been observed in many other animals. One such creature turns out to be pre-industrial man. Only recently have anthropologists and historians scrutinized the sleep of other cultures, earlier centuries and prehistoric humans. In the remarkably informative At Day's Close, Night in Times Past, Roger Ekirch unveils nocturnal life in the pre-industrial west.
Drawing from a broad range of sources he found a trove of evidence documenting our history of bimodal sleep. Until the late 1700s, and the widespread use of artificial light, people retired to bed soon after sun down and entered what was called "first sleep." They would awaken three or four hours later and enjoy a couple hours of quiet. During this time they often prayed, chatted about dreams and had sex. A French physician described this time between sleeps as a particularly good opportunity for sexual intimacy when couples "do it better" and have "more enjoyment." The middle night interactions seem to have been essential for social cohesion.
This was followed by "second sleep" that again lasted three to four hours and ended with sunrise. In fact, a study of contemporary cultures across the globe reveals a wide spectrum of sleep habits. Some anthropologists now speak of three sleep cultures: monophasic cultures (the West, where one consolidated sleep period dominates), siesta cultures (where one afternoon nap is added in the afternoon, the word siesta meaning the sixth hour) and polyphasic cultures (China, Japan, India where multiple naps throughout the day of varying lengths are the norm).
Researchers have replicated and expanded on Wehr's work. Several studies have taken subjects to deep underground bunkers free of any artificial light in order to observe our internal clock's rhythm. Again, they observe this biphasic pattern. Subjects sleep in two four-hour solid blocks separated by a couple hours of meditative quiet during which there is a remarkable surge of prolactin, unseen in modern humans. The participants report feeling so awake during the day that it is as if they experience true wakefulness for the first time.
So we find ourselves in a somewhat perverse situation. We have not evolved to naturally drift rapidly into one continuous nocturnal snooze. But according to the medical community and the pharmaceutical industry, if we don't do this, we suffer from a sleep disorder that merits medicating. However, if you ask any sleep expert how some people seem to fall asleep quickly and sleep continuously for seven or eight hours they'll say that such a sleep pattern is characteristic of chronic sleep deprivation.
We evolved in an environment of alternating light and darkness and developed internal clocks to manage in such conditions. Every known organism with two or more cells has an internal clock. In this regard, we are not unique. It is our use of artificial light to extend our day and defy our natural rhythms that distinguishes humans. We have just begun to understand the consequences of this Promethean sin.
Sleep deprivation has been linked to obesity, hypertension, insulin resistance, cardiac disease, and compromised immune function. In the same way that food products/supplements are replacing normal eating with dire health effects, sleep continues to be condensed by the 24/7 culture. The recent rapid growth of a new category of medications that promote wakefulness makes one wonder if sleep will soon be optional or ultimately obsolete.
So what can you do?
The constraints of work schedules and family responsibilities make radical changes in sleep-wake timing difficult. Here are some guidelines:
1. Abandon the idea of going to bed for six to eight hours of sleep at night (unless this works for you).
2. Get a feel for what your sleep cycle looks like. If you wake up before you need to, get up. This is probably a natural cycle end. You will make up for lost nighttime sleep with a nap(s).
3. Napping Guidelines:
4. If possible, when you feel like reaching for that afternoon caffeine fix, take a nap.
 Veasey S et al. Sleep Loss and Fatigue in Residency Training JAMA, Sept 4, 2002 Vol 288, No.9
 Sleep: A Comprehensive Handbook, edited by T. Lee-Chiong 2006 John Wiley & Sons p904
 Wehr T et al. In short photoperiods, human sleep is biphasic Journal of sleep research 1992 (2) 103-107
 Ekirch AR, At Day's Close, Nights In Times Past 2005 WW Norton & Co, Inc.
 C.M. Worthman and M. Melby. Toward a comparative developmental ecology of human sleep. 2002, In: Adolescent Sleep Patterns: Biological, Social, and Psychological Influences, M.A. Carskadon, ed. New York: Cambridge University Press, pp. 69-117.
 Ackermann K et al. Diurnal rhythms in blood cell populations and the effect of acute sleep deprivation in healthy young men. SLEEP 2012;35(7):933-940.
 Spiegel K et al. Sleep loss: a novel risk factor for insulin resistance and type 2 diabetes Journal of Applied Physiology Nov 2005 vol 99 2008-2019
 Knutson KL et al. The metabolic consequences of sleep deprivation. Sleep Medicine Reviews vol 11, Iss 3, 163-178 June 2007
 Gottlieb DJ et al. Association of usual sleep duration with hypertension. The Sleep Heart Study. Sleep vol 29, No 8, 2006
 Boutrel B et al. What keeps us awake: the neuropharmacology of stimulants and wakefulness-promoting medications. Sleep, vol. 27, No. 6, 2004
 Ko CH et al. Molecular components of mammalian circadian clock. Human Molecular Genetics 2006 15 (suppl 2) R271-R277
 Brooks A; Lack L. A brief afternoon nap following nocturnal sleep restriction: which nap duration is most recuperative? SLEEP 2006; 29(6):831-840.