Powerful delta brainwaves erupt in our heads. Our bodies release a deluge of hormones and proteins. From cardiovascular to digestive, our body’s systems automatically recalibrate.
This is deep sleep - otherwise known as “NREM” (or non-REM) stages three and four.
It’s the physically-reparative stage of sleep. It allows our bodies to heal worn-down muscles and replenish exhausted energy supplies.
But it does so much more than that. During deep sleep, we process memories, reinforce our immune systems, and wash away harmful toxins from our brains.
Deep sleep prevents an escalation of this physiological stress that is synonymous with increased blood pressure, heart attack, heart failure, and stroke.
Dr. Matthew Walker,
Why We Sleep
Deep sleep is a time of literal stillness. Our heartbeat slows and our breathing relaxes. Although our muscles are not paralyzed as they are in REM sleep, our bodies are quiet and calm. Even our metabolism slows, conserving energy for the upcoming day.
But this stillness belies a flurry of internal activity.
The pituitary gland pumps out growth hormones, which stimulate cell reproduction and regeneration. We replenish reservoirs of adenosine triphosphate (ATP) - the energy currency of the body - in preparation for another day.
Instead of waking weary and fatigued, deep sleep allows us to rise physically rejuvenated and energetic.
Deep sleep releases proteins, hormones, and therapies that repair our bodies and restore our energy. If it were a commercial service, it would be a billion dollar industry. But it is within us naturally and is available for free, every night.
Param Dedhia, MD
As our heart rate slows, our blood pressure drops. Deep sleep provides an opportunity for homeostatic recalibration. Simply put, it’s good for your heart.
Our digestion follows a similar process. With a break from the inflammatory process of eating, our digestive system can relax, recalibrate, and optimize its function for the next day.
Although we are unconscious, our minds are highly active.
Sharp wave-ripples fire in the hippocampus. Large-amplitude slow oscillations erupt in the cortex. Together, the two brain structures cooperate to convert short-term episodic memory into long-term memory.
Deep non-REM sleep almost hits the save button on those recently acquired informational pieces so that when you wake up the next morning, you have remembering rather than forgetting.
Without sufficient deep sleep, our bodies will not recover from the stresses of our waking lives. We will wake feeling fatigued. Our muscles will ache and our joints grind. With our energy supplies depleted, exhaustion will arrive early, wearing us down further.
Unbeknown to us, insufficient deep sleep also wreaks havoc on our cognition. Memories that were crystal clear yesterday will fade into the ether, half-remembered or wholly forgotten.
Without deep sleep cleansing our minds, toxic proteins like amyloids will accumulate, killing the surrounding cells and leading to degenerative illnesses like Alzheimer's.
Deep sleep deprivation need not be long-term to deliver harm, either. Just one night of four hours of sleep will drive a 70% reduction in immune cell activity.
To increase our deep sleep, we must first create the opportunity for it to exist. That means spending enough time in bed. While the old adage advises eight hours of sleep, the CDC prescribes between seven and nine.
But being unconscious for nine hours is rarely enough. The quality of our sleep is impacted by our environment, personal health, and life choices, and continues to change and evolve.
Modern sleep science uncovered a link between temperature and deep sleep. By reducing our core temperature by one or two degrees in the first half of the night, our bodies more readily slip into deep sleep.
The phenomenon’s cause lies in evolutionary biology. Our bodies adapted for natural caves and basic outside shelters - environments that grow cool and dark overnight. Modern bedrooms couldn’t be more different. While sleep scientists recommend temperatures between 60°F and 66°F, most Americans set their thermostats much higher.
We designed the Restorative Bed by Bryte to address the disparity between biological presets and modern life. It uses chilled air to emulate natural sleeping conditions, lowering the sleeper’s core body temperature and promoting the same deep sleep our ancestors would have enjoyed.
But our environment is only half the equation.
Many common substances have sinister sleep side effects.
Consider sleeping pills. The medicines target a set of receptors in the brain to induce a state of unconsciousness - a poor imitation of sleep. In fact, while sleeping pills induce “sleep,” they stymie progression into deep sleep.
The quality of sleep that you have when you’re on these drugs is not the same as normal, naturalistic sleep. They’re classified as “sedative hypnotics,” so the drugs actually just sedate you - and sedation is not sleep.
Alcohol performs a similar function. It lulls people to sleep, but prevents them from reaching the physically restorative deep sleep stage. With both sleeping pills and alcohol, those who take them often wake feeling groggy, weary, and fatigued - despite having “slept” for eight hours.
Caffeine, too, can hinder deep sleep, although the mechanics are different. The chemical blocks adenosine from entering the brain, staving off sleep. When we do slip into a caffeinated sleep, it is often fitful and disrupted. And if our sleep cycles are broken, we often return to the start, preventing us from reaching later stages like deep sleep.