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The Science and Mystery of Sleep











Sleep is essential throughout most of the animal kingdom. All warm-blooded animals—mammals and birds—sleep. Most cold-blooded animals—including reptiles, amphibians, fish, worms, and insects—sleep as well.

       Sleep is deeply rooted in evolution. When we consider that the very activity of sleep reduces vigilance and awareness in world full of hazards and dangers, the reason that Nature almost universally demands that animals sleep poses a mystery.

       The amount of time spent in sleep varies widely by species. Among mammals, giraffes spend as little as one-half hour sleeping (about 2% of the day). Horses sleep about 4 hours (about 17% of the day). Humans require about 8 hours (about 33% of the day) for optimal well-being. Dogs sleep about 10 hours (over 40%). Cats sleep about 12-15 hours (50% or more). A lion can sleep 21 hours (nearly 90% of the day).

       Most birds and mammals experience distinct stages of sleep, much as humans do. Of particular note, REM (Rapid Eye Movement) sleep is the stage when most dreaming occurs. Slow-wave sleep (SWS), characterized by the brain’s production of Delta waves, is the stage of high-quality, deep, restorative, dreamless sleep, when cellular regeneration and tissue repair is at its height. Among birds and mammals, both REM and SWS appear to play an essential role in learning and memory.

       Reptiles do not have a REM stage of sleep at all, suggesting that restorative SWS has deeper evolutionary roots. The absence of a REM sleeping stage among reptiles also leaves a virtually unanswerable question:  Do reptiles dream? Perhaps yes, but surely not as we do.

       In our society, most people simply don’t get enough sleep. An estimated 50 to 70 million Americans suffer with some type of sleep disorder. Common sense tells us that a good night’s sleep is beneficial and that without it we struggle through the day. A single sleepless night can make us irritable and sour our mood the next day. Multiple nights of insufficient sleep can hinder judgment, increase risk of accidents and injury, disrupt our ability to remember, and impair our ability to learn. We lose focus and attention.

       Chronic sleep deprivation can depress the immune system, lead to obesity, high blood pressure, heart disease, diabetes, and shorten life span. Complete insomnia is incompatible with life. In the rare genetic disease, Familial Fatal Insomnia, symptoms first appear around the age of 50 with loss of REM sleep and dreaming. The disease progresses to complete insomnia, at which point death follows in a month.

       Good quality sleep is essential to the regulation of hormone balance, which is key to our health and well-being. For example, growth hormone (GH) produced during sleep facilitates deep, restorative SWS (Delta wave sleep), when tissue and cellular regeneration are at their height. GH has many beneficial and anti-aging effects including increased energy, increased muscle mass, decreased body fat, and decreased sagging of tissue that comes with aging. However, levels of GH normally decline with aging, and this partly accounts for the shallower and less restful sleep, commonly seen among older individuals. Too little or low quality sleep itself blunts production of GH, causing us to miss out on the many anti-aging benefits that this hormone confers.

       While science puzzles over the reasons for sleep, the wisdom of Nature holds firmly that sound and sufficient sleep is essential—to good health, good mood, good judgment, mental focus and sharpness, resistance to infection, and resiliency in facing the stresses of life.

Dr. Cohen received his MD from Rutgers - New Jersey Medical School (1985), his ND from Bridgeport University School of Naturopathic Medicine (2004), and has practiced Integrative Medicine since 1994. His practice, Next Generation Medical & Wellness, is located at 75 Bloomfield Avenue, Suite 106, in Denville. For information, call 908-455-2639 or email


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