We now know that many neurotransmitters and hormones affect our sleep. It is an intricate system indeed. 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 sleep deprivation heart rate variability rises. In addition central nervous system activity is elevated and our environmental response system is activated. 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

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. As we age sleep tends to become less efficient and more fragmented.

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. 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.. The important information learned during the day needs to meld into old memories so as to update older information.