We often think of sleep as a simple on/off switch. We either get enough hours, or we don't. But I believe that unlocking better health isn't just about the quantity of sleep, but the quality. For anyone with chronic conditions, or anyone who wants to prevent them, understanding the stages of sleep and focusing on quality, not just quantity, is a powerful first step.
Understanding Your Sleep: Stages, Efficiency, and Quality
To truly understand sleep, we need to go beyond the hours on the clock. Sleep is a complex, cyclical process with two main phases: Non-Rapid Eye Movement (NREM) and Rapid Eye Movement (REM).
- NREM Stage 1 (Light Sleep): This is the transition from wakefulness to sleep. It’s a very light stage, and you can be easily awakened.
- NREM Stage 2 (Light Sleep): Your heart rate and breathing regulate, and your body temperature drops. You spend the majority of your night in this stage.
- NREM Stage 3 (Deep Sleep): This is the most crucial, restorative phase. Your heart rate and breathing are at their slowest, and your body focuses on physical repair, tissue growth, and strengthening the immune system. This is where your brain performs its "housekeeping."
- REM Sleep: This is the "dream stage." Your eyes move rapidly, your brain becomes highly active, and your body's muscles become temporarily paralyzed. REM sleep is critical for memory consolidation, emotional processing, and learning.
The quality metrics that matter
Two ideas make sleep quality concrete.
- Sleep efficiency, which is the ratio of time you actually spend sleeping to the total time you spend in bed. A high efficiency means you are using your sleep time effectively.
- Continuity and fragmentation, which is how often and how long you are awake after falling asleep. WASO (Wake After Sleep Onset), and the number of awakenings are the simplest ways to track this.
Add two more signals and you have a useful picture.
- Percent deep sleep, a proxy for physical recovery and glymphatic cleanup.
- Percent REM sleep, a proxy for memory and emotion processing.
In my work on Trillies+, we weight deep and REM more than raw hours, so an eight hour, choppy night does not masquerade as a great night.
What good usually looks like, your mileage may vary
- Efficiency: 85 to 90 percent or higher
- WASO: less than 30 to 40 minutes
- Deep sleep: often around low to mid teens as a percent of the night in midlife, higher in youth, lower in older age
- REM sleep: commonly around one fifth to one quarter of the night
Medication, age, illness, and schedule shifts change these targets, so treat them as general landmarks, not strict rules.
Why Quality Sleep Fights Chronic Conditions
My research at Trillies+ focuses on how these sleep metrics are causally linked to our health. The connections are not a coincidence; they are direct biological mechanisms.
- Diabetes: Poor sleep can lead to insulin resistance, a key factor in type 2 diabetes. When you're sleep-deprived, your body's ability to use insulin effectively is compromised, leading to higher blood sugar levels. A lack of sleep also affects the hormones that regulate appetite, increasing cravings for high-carb, sugary foods, which can make blood sugar management even more difficult. Conversely, good sleep helps your body regulate blood sugar and maintain healthy insulin sensitivity.
- Hypertension (High Blood Pressure) and Cardiovascular Disease: During healthy sleep, your blood pressure naturally dips, giving your heart and blood vessels a crucial rest. This is called "nocturnal dipping." Poor sleep, especially fragmented sleep or sleep disorders like sleep apnea, can disrupt this pattern, leading to consistently elevated blood pressure. Over time, this constant strain on the cardiovascular system increases the risk of hypertension, heart attacks, and strokes. Quality sleep also helps to reduce stress hormones like cortisol, which can elevate blood pressure.
- Chronic Kidney Disease (CKD): A significant portion of people with CKD also have sleep disorders, particularly restless legs syndrome and sleep apnea. Poor sleep can further compromise the body's ability to repair itself and regulate fluid balance, which is already a challenge for people with CKD. It's also associated with increased inflammation and stress on the body, which can exacerbate kidney damage.
- Mental and Emotional Health (The Critical Role of REM Sleep): REM sleep is essential for emotional regulation and processing the day's events. During this stage, your brain works to consolidate memories and manage emotional experiences. When you're deprived of REM sleep, your ability to cope with stress is impaired, leading to increased anxiety, irritability, and a heightened stress response. This is directly linked to an increase in stress hormones, such as cortisol. High, sustained cortisol levels not only impact mood and mental health but also contribute to high blood pressure and other physical health issues. In this way, poor sleep creates a vicious cycle: stress impacts sleep, and poor sleep makes you less able to handle stress.
- Overall Chronic Disease Management: Beyond the specific physiological effects, poor sleep can have a ripple effect on a person's ability to manage their condition. Fatigue, irritability, and impaired cognitive function can make it harder to adhere to treatment plans, such as remembering to take medication, following a specific diet, or engaging in regular exercise. This can lead to a vicious cycle where poor sleep worsens the disease, and the disease's symptoms, in turn, disrupt sleep.
The Link Between Deep Sleep and Dementia
The brain's "housekeeping" system is most active during deep sleep, and this function is crucial for preventing the buildup of toxins associated with neurodegenerative diseases like Alzheimer's.
- The Glymphatic System: The brain has a waste-removal system called the glymphatic system. This system functions like a lymphatic system for the brain, using cerebrospinal fluid to flush out waste products that build up during the day. This process is most active and efficient during deep, slow-wave sleep.
- Clearing Amyloid-Beta and Tau Proteins: The glymphatic system is responsible for clearing toxic proteins like amyloid-beta and tau. The accumulation of these proteins is a hallmark of Alzheimer's disease. Studies have shown that poor sleep quality, specifically a lack of deep sleep, is associated with higher levels of both tau and amyloid-beta in the brain.
- Memory Consolidation: Deep sleep is essential for declarative memory consolidation (memory for facts and events), while REM sleep is important for procedural memory consolidation (memory for skills and tasks) and emotional processing. A lack of deep sleep can hinder the brain's ability to form and retain new factual memories.
In short, deep sleep is the brain's primary time for cleaning and repairing itself. For individuals at risk of dementia, this process is a vital line of defense against the accumulation of harmful proteins and the cognitive decline that defines the disease.
How Can Deep Sleep and REM Sleep Be Extended and Improved?
The good news is that you can take active steps to improve your sleep quality. Many of the same strategies apply to both increasing deep sleep and reducing disruptions like WASO.
- Set a Stable Anchor: Choose a consistent wake time, seven days a week. Bedtime will self-adjust once your body trusts the schedule.
- Protect a 60-Minute Wind Down: Dim lights, reduce screens, and lower the emotional temperature of your evening. This helps calm the mind, which is essential for emotional processing during REM sleep and for achieving the deep relaxation needed for slow-wave sleep.
- Caffeine Cutoff: Aim for none within six to eight hours of bedtime. If in doubt, move your coffee earlier for one week and watch your efficiency and WASO.
- Alcohol Caution: Alcohol shortens the time it takes to fall asleep but fragments the second half of the night and reduces REM. If you drink, finish early and test two alcohol-free nights midweek.
- Exercise Regularly: Consistent physical activity is one of the most effective ways to boost the amount of restorative deep sleep you get. However, avoid strenuous workouts right before bed, as the endorphins can keep you awake.
- Eat Fiber-Rich Foods: A diet high in fiber has been linked to spending more time in the restorative stages of deep sleep.
- Optimize Your Sleep Environment: Make your bedroom a sanctuary for sleep. Keep it dark, quiet, and cool (the ideal range is often cited as 60-67°F or 15-19°C). Use blackout curtains, earplugs, or a white noise machine if needed.
- Taper Fluids Before Bed: If frequent nighttime urination is a problem, try reducing your fluid intake two to three hours before bedtime.
- Get Out of Bed: If you're awake for 20 minutes and can't fall back asleep, get out of bed. Do a quiet, low-stimulation activity in another room until you feel sleepy again. This preserves the mental association between your bed and sleep.
When to Talk to a Clinician
Snoring with witnessed pauses, choking or gasping at night, morning headaches, or persistently unrefreshing sleep despite good habits are red flags for sleep apnea. Restless, creepy sensations in the legs at night can point to restless legs syndrome. If you see these patterns, get evaluated, as home treatment hacks won't fix a medical sleep disorder.
Sleep is not just a passive activity; it is a powerful preventative health measure. While being active and eating well are essential, they can't fully compensate for a lack of quality sleep. The body's ability to repair, regulate, and detoxify hinges on consistent, high-quality rest. By taking control of your sleep, you empower your body's natural ability to manage chronic conditions, improve your cognitive function, and secure your long-term health.
About the Author
Darren S. is the founder of Trillie Inc., bringing over 20 years of experience in technology and product management. He is passionate about advancing causal AI and building sustainable solutions that make practical, affordable technology accessible to people and communities everywhere. Connect on LinkedIn