I can think of few things as satisfying as a good night sleep. As I age, it seems harder and harder to achieve. Sleep is extremely important to humans and there are some significant consequences to not getting enough.

Sleep is essential in a diverse range of organisms ranging from nematodes, insects, amphibians, birds, reptiles and mammals. In humans, sleep loss contributes to obesity, elevated blood pressure and metabolic disorders. It can also lead to changes in cognition, behavioral changes and neurological issues affecting judgment, reaction time and mood.
The sleep cycle has four stages followed by REM or rapid eye movement sleep. As we sleep, our heart rate is reduced, core body temperature drops and electrical activity in our brain changes. During Stage 1, we drift in and out of wakefulness and we can easily awaken. In Stage 2, eye movement stops and brain waves slow. We spend about one half of our sleep time in Stage 2 sleep. In contrast, Stage 3 is a deeper sleep that is harder to wake from and may cause disorientation after abrupt awakening. Brain waves are slower with some occasional faster waves. During Stage 4, these slow waves predominate and it becomes harder to arouse someone. After Stage 4, REM sleep occurs, 70 to 90 minutes after sleep cycle initiation. During REM, heart rate increases, breathing becomes more rapid and shallow, eyes move irregularly and we dream. About 30 percent of our total sleep is in the REM stage. A complete sleep cycle is about two hours long so we complete several cycles each night. Who knew sleep could be so complicated.

Sleep deprivation leads to changes in brain waves as measured by electroencephalogram that reflect changes in neural activity in different areas of the brain. In the stratum, receptors for the brain messenger chemical dopamine are affected. In the forebrain, buildup of nitrous oxide leads to accumulation of adenosine which has sedative activity and whose elevated levels correlate with sleepiness and decrease after sleeping. Caffeine blocks adenosine receptors and keeps us awake. So that’s why there should be no Joe at bedtime.

Even short duration sleep deprivation alters our metabolism which can resemble prediabetic states. This can lead to changes in insulin signaling and in activities of genes in fat cells called adipocytes contributing to obesity. Sleep debt also alters brain wave patterns, emotions, cognition and behavior and increases appetite. Those in sleep debt consume hundreds of additional calories every day.

We still do not fully understand the impact of chronic sleep debt on health. Sleep deprived rodents show some profound effects including reductions in bone formation and alterations in bone marrow composition. The length of the small intestine increases, hormone levels such as leptin and corticosteroids change, cholesterol levels are altered and skin changes lead to irritation and sores. In humans, chronic sleep deprivation can increase the possibility of heart attacks.
So sleep is much more than closing your eyes for some time each day. If you are having sleep problems, your physician could recommend a sleep specialist. Overall, good lifestyle habits, a defined sleep schedule and minimizing factors that are sleep disruptive are important.

Medical Discovery News is a weekly radio and print broadcast highlighting medical and scientific breakthroughs hosted by professor emeritus Norbert Herzog and professor David Niesel, biomedical scientists at the University of Texas Medical Branch at Galveston. Learn more at