In 1900 Americans slept an average of ten hours a night. Today, in 2001, the average American sleeps only six and half-hours nightly. All animals sleep, but no other animal willingly sleep deprives itself. It has been known for some time that severe sleep deprivation in rats is always fatal. This is because of the disruption in immune system function that comes with sleep restraint. We are not wired for sleep deprivation. Sleep is a necessary and incredibly complex and important restorative function. It profoundly affects our brain, immune system, body temperature regulation, and digestion. For instance, with chronic sleep deprivation cortisol, a stress hormone, is elevated. This is a stress hormone that has many functions. A chronic cortisol elevation subjects our body to sustained arousal and stress. With normal rest (approximately eight hours seems to be the minimum) our cortisol decreases dramatically, which results in resilience and restoration of our basic environmental interaction response system. Sleep deprivation prevents recovery from daily environmental stimulation. With sleep deprivation heart rate variability rises. In addition central nervous system activity is elevated and our environmental response system is activated.
There are many conditions and drugs that cause sleep disruption. Alcoholism, for example, promotes poor sleep. Addiction causes changes in dream sleep stages and loss of deep sleep. Alcoholics, like the elderly, have poor sleep efficiency. Elevated nightly cortisol and decreased time before the start of dream sleep are biological markers of depression and aging. Sleep loss usually impacts upon mood states, typically resulting in depressive mornings and improved mood recovery in the afternoon. Childhood stress tends to decrease time before the start of nightly dream sleep; a phenomenon mentioned earlier relating to depression, which seems to predispose some people to adult sleep disruption. Sleep loss is a risk factor for depression.
If you scan the brain of a sleep deprived person, it looks very different than when sleep has been restored. Our frontal lobes, part of our "higher" thought center, are particularly effected. Sleep loss certainly feels like a "foggy" brain to most of us. Interestingly, study after study indicate that people who are habitually sleep deprived are notoriously poor at evaluating the reality of their deficits. Even though sleep deprived individuals often protest that they are fine with decreased sleep, they inevitably test poorly on cognitive and motor reflex skills.
We now know that many neurotransmitters and hormones affect our sleep. It is an intricate system indeed. During our sleep natural killer cells, an important part of our immune system increases. These cells decrease with sleep loss. In normal people interlukin six is a circadian factor, which effects our body's normal rhythms and cycles. Interlukin six increases throughout the night and, levels off after around midnight. The exaggerated increase in interluken six in alcoholics serves to inhibit the natural homeostasis and recovery of the body. Arthritic people also show high levels of interluken six. There is some evidence that the lack of modulation of interluken six results in a physical inflammatory reaction.
Chronic partial sleep loss results in a reorganization of the sleep cycles with more dream stage sleep loss. When we rest again, there is a dream sleep stage rebound. Early life events modulate dream sleep. It is primarily in dream sleep that we consolidate in memory information that has been learned the previous day. Thus if dream sleep is disrupted, learning is disrupted. This has enormous implications for children. Adolescents lean towards a twenty-seven hour sleep cycle, predisposing them to later nights and later awakening. Our school system, of course, is set up on the opposite clock, early to rise and early to dismiss, a pattern much more suited to the biological clocks of older adults. It is thought that most children, including adolescents, require approximately a ten-hour night of sleep. The important information learned during the day needs to meld into old memories so as to update older information. As we age sleep tends to become less efficient and more fragmented. There is an increase in nighttime cortisol and a decrease in dream sleep time. This can result in enormous systemic physical stress, and of course loss of sleep at any stage disrupts learning.
These thoughts refer only to a smattering of the burgeoning knowledge in sleep research, which is highlighting the significance of adequate rest. At every stage of life sleep is renewing. Its role in learning, cognition, memory consolidation, emotional well being, digestion and immune resiliency speak to us loudly as a daily activity that is to be respected and guarded as a life habit akin to nutrition and exercise, which of course interface with our sleep.
- Dr. Linda Klaitz, Medical Psychologist