Time is a great equalizer: Every one of us, from postal worker to president, is allotted the same twenty-four hours each day to do with as we see fit. Or so we think. For, even time—that one possession that no man can steal—is not fully under our control. Indeed, there is something more powerful than a man’s will: his need for sleep.
Still, we push the limits that nature has given us. In an endless race against the clock, we push the limits of our productivity. We trade pillows for problem sets and comforters for coffee. Inevitably there is a limit, but how far, and most importantly how long, can we push ourselves?
Evolutionarily, sleep does not necessarily seem to present an obvious advantage. At first glance, sleep is not particularly efficient. Humans and other animals spend hours a day lying still and defenseless while predators, prey, and the demands of life continue their progress. So why is sleep so necessary, and what happens when we do not get enough?
Researchers find it much easier to answer the latter of the two questions. Sleep-deprivation is a common occurrence in modern culture, and it is studied frequently as well. Anecdotal evidence leads us to believe that psychological factors such as alertness and mood are negatively affected.
Research shows this to be true to a startling degree: After only 17 to 19 hours without sleep, subjects have been shown to have response speeds up to half as slow as well-rested individuals, and on some tests perform equivalent or worse than those with a blood alcohol level of 0.05%, the legal limit in most western European countries.
Mood can be affected dramatically as well. In clinical studies with depressive patients, insomnia has been reported to be as frequent as 60%, and between 10% and 20% of individuals complaining of insomnia also suffer from depression. Frighteningly, results suggest a directional pattern of development from insomnia to depression independently of age.
Sleep deprivation can also wreak havoc on the body. Particularly low or high levels of sleep (less than 6 hours or more than 9 hours each night) has been associated with increased prevalence of diabetes and impaired glucose tolerance.
Moreover, lack of sleep has recently been implicated in the obesity pandemic. Individuals who sleep for 5 hours a night were found to have 15% more ghrelin, a hormone that increases feelings of hunger, than those who slept for 8 hours. They were also found to have 15% less leptin, a hormone which suppresses appetite. These hormonal changes are thought to cause increased feelings of hunger, eventually leading to weight gain.
This can precipitate a catch-22 situation, as obesity can lead to sleeping disorders such as sleep apnea. Sleep debt has also been shown to negatively impact on carbohydrate metabolism and endocrine function. These effects described in these studies are comparable to those seen in normal aging and, as such, sleep deprivation may amplify the severity of age-related chronic disorders.
While these studies may be unnerving, analysis of sleep deprivation is helping to shed light on the process and on the necessity of sleep itself. Sleep has long been assumed to be restorative, helping an organism recoup and prepare for the next bout of activity. Recent research has helped to shed light on the details of that process.
One analysis of mouse cerebral cortex and hypothalamus shows that gene expression varies significantly following different durations of sleep and periods of sleep deprivation. The amount of variation between states is astounding: 3,988 genes in the cerebral cortex and 823 genes in the hypothalamus were found to be altered depending on the amount, or lack, of sleep.
Tellingly, the leading classes of over-represented genes with increased expression with sleep are those genes involved in biosynthesis and transport. Many of the above-mentioned genes encode enzymes involved in cholesterol synthesis, and proteins needed for lipid transport and for energy-regulating pathways.
Another study on rats has shown that sleep deprivation for 72 hours leads to higher levels of the stress hormone corticosterone. This increase in hormone then affects the hippocampus, a region of the brain involved in the formation of memories. When the rats are sleep-deprived, this area of the brain slows its production of new cells, perhaps in response to the increased hormonal levels. If this is indeed the case, it could indicate profound long-term structural changes in the brain in response to sleep deprivation.
Another way in which sleep deprivation can help explain the biological processes of sleep is through analysis of sleeping disorders. Sleeping disorders are ubiquitous: 50 percent of adults are affected with 1 or more sleep problems. Even the more severe, well-known disorders are more common than they seem.
For example, narcolepsy affects as many individuals as multiple sclerosis or Parkinson disease. Research on Morvan’s syndrome, a diseases marked by a drastically reduced need for sleep, shows that this disease may be attributed to serum antibodies targeted against particular potassium channels in cell and nerve membranes.
Since these channels help shape action potentials in neurons, this may help explain the symptoms of this disease. Together, these experiments give insight into the restorative processes of sleep, whether by enhancing macromolecule biosynthesis, allowing neuronal proliferation, or enabling potassium channels.
Clearly, there is still much to be learned about the effects of sleep deprivation and the restorative processes of sleep. No matter how much knowledge is gained, however, it seems unlikely that man will be able to push back against his own mind to conquer the necessity to let body, and mind, take a rest.