Remember the six phases of sleep which make up the 90 minute sleep cycle? It is during the last three (deepest) phases that we get our best rest. During deep sleep we inhibit the production of a hormone called ghrelin which increases appetite, while stimulating the release of a substance called leptin which turns off the desire to keep eating. Deep sleep is also the time when we replace dopamine and serotonin, two important brain chemicals which bring feelings of comfort and satisfaction. Lack of deep, restorative sleep leads to depressed mood and leaves us craving comfort foods typically high in starch, sugar, and fat. Eating to self-soothe can become an addiction and is one of the chief features of obesity. Obesity in turn can interfere with sleep by making it harder to breath while in the deepest (most fragile) phases of sleep, often knocking us out of REM to restart the cycle at phase one. Lack of REM causes us to wake feeling tired with our hormone levels unrestored and our brain circuits unrefreshed, reinforcing the cycle of depressed mood, comfort food cravings, and weight gain.
The 90 Minute Cycle
Let’s break it down. Sleep takes place in ninety minute cycles. Each ninety minute cycle is broken down into six phases. In the first phase known as latency or ‘pre-sleep,’ we are just beginning the process of going unconscious. During this phase, two neurotransmitters (adenosine and GABA) as well as a hormone called melatonin (more about this later) act to lower body temperature, slow down brain activity, and inhibit body processes associated with wakefulness. We are not yet asleep, but we are no longer fully awake. Latency is followed by Phase I sleep, the first level of unconsciousness. At this point we no longer have awareness of our surroundings–we are asleep. Each of the four successive phases represent progressively deeper levels of sleep.
As we go into the deepest levels the body undergoes profound physiological changes, releasing certain hormones and neurotransmitters, inhibiting the release of others, refreshing our brain circuitry, mobilizing the armed forces of the immune system to fight viruses and bacteria which infect us each day. During deep sleep our bodies go to work repairing stressed and damaged muscle, tendon, ligament, and skin tissue, and burning fat from our waists. Paradoxically, the deepest phases of sleep are also the most fragile; they can be easily disturbed by movement, noise, light, or other stimuli.
The sixth (deepest) phase of sleep, called ‘REM’, is the phase during which we dream. It is also the phase during which the most important physiological restoration takes place. We cycle down to REM sleep and then back up to phase one, light sleep, over a period of ninety minutes. As adults, in order to get full restoration of our health we must have a minimum of four of these ninety minute cycles each night, but ideally we should have five to six of them. Each successive cycle includes more time spent in REM.
How Much Sleep Do I Need?
Men need about eight hours of sleep each night. Women cycle through the phases of sleep slightly faster and on average need about seven to seven and a-half hours. But these numbers vary from individual to individual. I do best at seven hours and fifty minutes, which is pretty typical for men. My wife (whom I believe to be part cat) does best with just shy of nine hours.
Do We Need Less Sleep As We Age?
There is a myth that as people get older they need less sleep. In fact, while it is true that people tend to get less sleep as they age, is is not true that they need less sleep. There is a tiny structure, about the size of a small pea, which lies in the center of the brain, just behind the eyes. It is called the pineal gland and it produces a serotonin-based hormone called melatonin which helps to induce and maintain the sleep state. The pineal gland is the only endocrine gland that has communication with the outside world. It senses light through activation of receptors behind the eyes. In the absence of light, these receptors are quiet, and the pineal gland secretes melatonin which makes us sleepy and helps us to cycle down into deeper sleep. In the presence of light, the receptors become stimulated (even when the eyes are closed) causing them to signal the pineal gland to stop producing melatonin and initiating a reflex to induce wakefulness. The production of sleep-inducing melatonin in the dark and the shutting off of melatonin production in the presence of light, ties us to the cycles of day and night. The pineal gland is the control center of our circadian rhythm.
The pineal glands of babies produce a lot of melatonin. A little less gets produced during childhood, but it is still a lot compared to the precipitous decline which takes place during adulthood. By the time we reach the age of 50, our pineal glands are able to produce only about 25% the amount of melatonin that we produced in our teen years. By age 70 we produce only 5-10%. High levels of melatonin production in infancy and childhood help to explain why children are able to drop suddenly into such deep sleep and to maintain sleep for nine, ten, or more hours. Similarly, progressively lower levels of melatonin helps account for the difficulty many people experience getting adequate sleep as they get older. But this does not mean that our bodies need less sleep as we age. It is more accurate to say that the aging process–the breakdown of healthy body tissues due to increased inflammation and diminished circulation–is exacerbated by lack of sleep, a problem which tends to accelerate as we age due in part to diminishing levels of melatonin.
I Get Enough Sleep, So Why Do I Still Feel Tired?
The right quantity of sleep is important for necessary restoration and recuperation. But equally important is the quality of the sleep that we get. Many of my patients report sleeping 7-8 hours per night, but they still wake up feeling tired and unrefreshed a clinically significant amount of the time (more than twice per month). Do you need coffee to get you going most mornings? Is it the rare morning when you wake up full of energy, feeling as though you’d slept just the right amount in order to feel great? If you are waking up feeling tired despite getting plenty of sleep, then you are probably experiencing poor quality sleep.
REM, the deepest phase of sleep, is also the most fragile phase and is very susceptible to disruption. Noise, light, difficulty breathing due to excess fat in the throat area (sleep apnea), back pain, neck pain, shoulder pain, even the pressure of a full bladder can be enough to nudge us out of this most important phase, either waking us up, or almost waking us and causing the cycle to restart at pre-sleep or phase I without having spent any or enough time in REM restoring our bodies and brains. This is how we are able to get eight or more hours of sleep yet still wake up feeling tired and unrefreshed. We are simply not spending enough time during those eight hours in the deep restorative phases of sleep, especially REM.
If we want to retire with enough savings to live comfortably then we need to have a strategy. We must put our strategy into place many years ahead of time and then stick to it until retirement. If we want to get into a good college, grow our business, become a success at virtually anything, we need to create the habits and behaviors which will move us gradually toward our goal. Health is no different. The AIL strategy starts by understanding that optimal health (within the limits of each of our genetic capability) is dependent upon five behaviors which must become incorporated into our daily lives as habits. These five behaviors, which I call the Five PIllars of Health, are as follows:
1) Proper nutrition
2) Specific supplementation
3) Regular exercise
4) Restorative sleep
5) Stress management
All is not just a strategy for longevity, it reflects my deeply held conviction that the quality of one’s life is as important as longevity itself. In this essay I will discuss the most overlooked pillar of health: sleep.
Sleep: The Most Commonly Overlooked Pillar of Health
Until the middle of the last century relatively little was known about sleep. Generally considered to be the time when we ‘recharge our batteries,’ few doctors and even fewer lay-persons have sufficient understanding of what sleep is and the essential role that it plays in our health and well-being. Immune function, brain function, tissue healing, regulation of body fat, hunger, and mood are all dependent upon sleep–deep, restorative sleep. Yet up to 70% of adults do not get enough of this vital restoration to move them in the right direction along the Health Continuum (see previous blog posts for more on the concept of the Health Continuum).
Only recently have issues like sleep apnea and restless leg syndrome become part of the general health conversation between doctors and patients, and these conditions form just the tip of a giant iceberg which includes diminished sex drive, low levels of testosterone, obesity, compulsive eating, depression and anxiety, chronic infections, and generalized inflammation–the underlying cause of most chronic diseases–all of which can be linked directly to lack of restorative sleep.