Why Do We Sleep?
We still do not know exactly why we sleep. Some scientists say we evolved to sleep because the inactivity surrounding sleep made us safer than animals wandering around when predators were on the hunt. Other scientists say that sleep is an excellent way to conserve precious energy needed for the challenging work of finding food when we are awake or of working to maintain our standing in our social community. Still other scientists suggest that sleep is the time the brain and body go through the energy intensive work of repairing the damage caused by the wear and tear of daily life. Finally, a more recent scientific theory is that it is primarily during sleep that we re-organize, filter and consolidate life's daily experiences so that they are handily available for us to draw upon in the future. You might say that sleep is nature's way of preparing us to live more wisely tomorrow. The bottom line is that all these theories have contributed to our growing understanding of sleep. But, there are still so many sleep mysteries to uncover.
Sleep: What's the Big Deal?
We know that the amount of sleep required by living creatures, including human beings, varies tremendously across species and across individuals. We know that sleep is a biologically hard-wired imperative, like eating, but it is so much easier to grasp the value of eating when compared to the less obvious ways in which sleep benefits us. Aside from feeling fatigued, "edgy" or less clear-headed, is there really something bad or unhealthy about short-changing our sleep?
The evidence is increasingly clear. Sufficient sleep is a pre-requisite for good health. Not only do most illnesses has a disruptive influence on sleep, the reverse is also true: When people are chronically deprived of restorative sleep, their risk of acquiring any number of health problems increases exponentially. (In Staying Sharp: 9 Keys to a Youthful Brain through Modern Science & Ageless Wisdom, my co-author and I detailed the risks of not obtaining enough sleep.)
What Unravels When We Don't Sleep Well
Here is a partial listing of some of the health risks connected to chronic sleep insufficiency.
· All energetic activity produces by-products. Driving cars produces emissions as a by-product of the internal combustion in our vehicle's engines. The by-product of our daily mental activities is the production of molecules, which are mainly proteins, that need to be cleared out. This occurs best while we sleep. The glymphatic system functions like a fluid flush, cleansing the brain tissue of waste molecules produced during the day. The ever-flowing river of lymph fluid that circulates through our brain and the length of the spinal cord allows the body and blood to remove these toxic metabolic byproducts from our central nervous system quietly and efficiently.When we skimp on sleep, these by-products build up over time, increasing our risk of premature cognitive decline and other health consequences.
· Like any complex system, our body's pieces and parts work best when they are in sync with one another. Our car's engine has a timing belt and other calibration and coordination mechanisms. There are many elements that have to fire at the precise moment in order for the car's overall performance to occur. Similarly, our body, which is infinitely more complex, relies on many timing mechanisms to keep all our pieces, parts, and processes working smoothly. Good health is a function of how well synchronized and regulated these activities are. When our sleep quality and quantity are chronically poor, dysregulation and lack of coordination among the various systems in our body develop. The many health problems that arise when sleep is poor reflects a breakdown or disruption to the body's chrono-biology (or its ability to work in a well-synchronized manner).
· Even in individuals without a history of depression or anxiety disorders, chronic sleep difficulties can contribute to the development of these potentially devastating mental/emotional difficulties. From a psychological health perspective, good sleep functions as a whole-brain/whole-body protector and emotional resilience strengthener.
· Chronic sleep deprivation leads our brains to develop "micro-sleep" patterns in which we will fall asleep for seconds at a time during the day, often without realizing it. When driving or engaged in other types of activities, the consequences of micro-sleep can be deadly. At a minimum, micro-sleep patterns mean that even when we may be present physically, we are often mentally "absent". The consequences to work and relationships can be significant.
· Chronic sleep deprivation erodes the efficiency of our immune system, which is critically important to fighting illness-causing agents. Because immune system activity is so energy intensive, it works best at night, when our energy is not otherwise directed into other physical activities.
· Cortisol, the molecule released when we encounter novel situations, especially threatening or high stress circumstance, remains higher when we are sleep deprived. At the same time, poor sleep lowers the production of leptin, a hormone telling you that you have had enough to eat, while simultaneously increasing the level of ghrelin, which acts to stimulate your appetite. Therefore, not only is sleep deprivation associated with weight gain, it is also linked to greater difficulty with shedding weight. It is as though the body perceives the sleep debt as a significant stressor and, in the face of that stressor, the body becomes possessive: it holds onto our extra pounds, refusing to burn fat calories in a valiant but self-defeating attempt to protect us against the stressor of not sleeping!
· A major pathway by which our brain and our bodies talk to each other is through the Hypothalamic-Pituitary-Adrenal Axis (HPA-Axis). This neuro-endocrine highway keeps our body's organ systems synced to what our brains perceive as the level of bodily arousal needed to cope with or contend with the demands of our external world. Unfortunately, chronic sleep deprivation acts as a chronic stressor to the brain. As a result, through the HPA-Axis, our body's organs are kept in a heightened state of chronic arousal. In essence, chronic sleep deprivation acts like an aging accelerant, prematurely aging every organ system in our body, including our brain. Life goes by fast enough. Getting enough sleep is the most direct and most efficient way of taking our foot off this damaging "life accelerator."
· Other documented consequences of insufficient sleep include a decline in our sex drive, an increase in motor vehicle and work-setting accidents, irritability and moodiness that chip away at relationship health, and mental cloudiness, including focusing/concentration problems and memory loss, especially for short-term memory functioning.
While the mystery of why we sleep remains, the centrality of good sleep to our daily lives and our long-term health is unquestioned. I will be devoting my next blog in this series to outlining accessible steps you can take to help you obtain the sleep your life requires. A simple preview: Many of the keys to disrupting or restoring our sleep are to be found in how we live our days. Stay tuned!