Medical Guidance on your Healing Path

The Science and Mystery of Sleep

Philip J. Cohen, MD, ND


Sleep is essential throughout the 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 wellbeing. 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 (warm bloods) 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, 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 are at their height. Reptiles (cold-blooded ancestors to both birds and mammals) do not have a REM stage of sleep at all, suggesting that restorative Slow-Wave Sleep has deeper evolutionary roots.

In our society, most people simply don’t get enough sleep. An estimated 50 to 70 million Americans suffer with some kind 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 (sleeping 4-5 hours per night) leaves us feeling depressed, anxious, stressed, physically and mentally exhausted, pessimistic, sad, angry, and less sociable — all of which improve with more normal sleep (8 hours/night). Chronic sleep deprivation leads to obesity, high blood pressure, heart disease, diabetes, depressed immune response, and shortened life span.

Good quality sleep is essential to the regulation of hormone balance, which is key to our health and wellbeing. Insufficient or low-quality sleep, on the other hand, creates hormone imbalances, which disrupt control of appetite, hamper our ability to maintain stable blood sugar, and decreases our level of energy.

For example, Growth Hormone (GH) produced during sleep facilitates deep, restorative slow-wave (delta wave) sleep, when tissue and cellular regeneration are at their height.

GH has many beneficial and anti-aging effects: GH increases energy, increases muscle mass, decreases body fat, and decreases 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.

Poor quality or insufficient hours of sleep creates other hormone imbalances, such as decreasing Leptin (a hormone that signals satiety) and increasing Ghrelin (a messenger that stimulates appetite), leading to food cravings and especially craving for sweets, even when we have eaten enough for our needs, which, in turn, blunts the production of GH. Inadequate sleep increases Cortisol, signaling a stress (distress) state and triggers increased Insulin, which promotes weight gain, thereby increasing the risk of high blood pressure, obesity, and diabetes.

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.