Most healthy adults spend 10 to 20 percent of their total sleep in deep sleep (the slow-wave stage) and 20 to 25 percent in REM sleep. If you’re waking up groggy or mentally foggy despite logging enough hours, the issue is often not how long you sleep but how much time your body spends in these two restorative stages. The good news: several straightforward changes to your habits and environment can shift the balance in your favor.
Why Deep Sleep and REM Serve Different Roles
Deep sleep and REM sleep do fundamentally different things for your body, and understanding the distinction helps explain why you need both. Deep sleep (also called N3 or slow-wave sleep) is concentrated in the first third of the night. This is when your body repairs tissue, strengthens the immune system, and consolidates physical recovery. Growth hormone release peaks during these slow-wave cycles.
REM sleep, by contrast, spreads across four to five episodes throughout the night, with the longest stretches happening toward morning. REM is when your brain processes emotions, solidifies learning, and clears metabolic waste. Cutting your night short by even an hour disproportionately costs you REM, because you’re losing those late-morning episodes.
Keep Your Bedroom Cool
Your core body temperature needs to drop by about one to two degrees Fahrenheit for sleep to initiate and stay stable. A warm room fights that process. Cleveland Clinic sleep psychologist Michelle Drerup recommends keeping the bedroom between 60 and 67°F (15 to 19°C). That range supports both slow-wave sleep and REM stability. Thermoregulation is one of the most direct levers you have: if your body can’t cool down, it struggles to stay in the deeper stages.
If you run hot, consider breathable bedding materials like cotton or bamboo, and skip heavy comforters. Wearing socks to bed can paradoxically help by dilating blood vessels in your feet, which pulls heat away from your core faster.
Lock In a Consistent Sleep Schedule
Your brain’s internal clock dictates when it cycles through each sleep stage. An irregular schedule, where you go to bed at 10 p.m. on weekdays and 1 a.m. on weekends, disrupts those transitions. Your body essentially recalibrates each night, producing shallower and more fragmented sleep in the process.
The single most effective scheduling change is fixing your wake time. Waking at the same hour every day, including weekends, anchors your circadian rhythm more powerfully than a consistent bedtime does. Your body will start to anticipate sleep onset and arrange its deep sleep and REM windows more efficiently. If your schedule has been erratic, expect it to take one to two weeks of consistency before you notice a difference.
Time Your Exercise Right
Regular aerobic exercise is one of the most reliably studied ways to increase deep sleep. People who exercise consistently tend to spend more time in slow-wave stages and report feeling more restored in the morning. The effect builds over weeks, so a single workout won’t transform your sleep, but a sustained habit will.
Timing matters. Harvard Health notes that high-intensity exercise less than one hour before bedtime increases the time it takes to fall asleep and reduces overall sleep quality. A reasonable guideline is to finish vigorous activity at least two hours before bed. Moderate exercise, like a brisk walk or gentle yoga, is generally fine later in the evening.
Limit Alcohol, Especially Before Bed
Alcohol is one of the most potent REM suppressors in everyday life. Even a couple of drinks in the evening can dramatically reduce the amount of REM sleep you get in the first half of the night. Your brain then tries to compensate with a “REM rebound” later, which often fragments your sleep and causes vivid dreams or early waking.
The American Academy of Sleep Medicine has found that chronic alcohol use can produce lasting changes to REM regulation that persist even during long periods of sobriety. For occasional drinkers, the fix is simpler: stop drinking at least three to four hours before bed, or limit yourself to one drink earlier in the evening. If you’re tracking your sleep with a wearable and noticing low REM percentages, alcohol is the first variable to eliminate.
Manage Light Exposure Strategically
Bright light in the morning and dim light in the evening is the basic formula for a well-timed circadian rhythm. Morning sunlight within the first hour of waking suppresses melatonin and sets your internal clock, which pays dividends later when your brain needs to cycle through deep and REM stages at the right times.
The evening side is more nuanced than many sources suggest. A study from the European Sleep Research Society found that two hours of blue-enriched light exposure in young adults did not significantly delay REM onset compared to warmer light. However, research in older adults did show longer REM latency after multiple evenings of light exposure. The takeaway: evening screen use probably matters more as you age, and cumulative exposure over several nights is a bigger concern than a single evening. Dimming your lights and using warm-toned screens in the last hour or two before bed is a sensible precaution, even if the effect isn’t as dramatic as often claimed.
Nutrients That Support Sleep Stages
Glycine
Glycine, a simple amino acid found in bone broth and collagen-rich foods, enhances sleep by accelerating the natural drop in core body temperature before bed. It increases blood flow to the extremities, pulling heat away from your core faster than your body would manage on its own. Clinical research has consistently used 3 grams as the effective dose, taken shortly before bed. At that dose, studies show smoother transitions between sleep stages and more restorative deep sleep, with the effect being notably weaker at smaller amounts.
Magnesium
Magnesium plays a role in calming the nervous system and relaxing muscles, both of which support the transition into deeper sleep. A randomized, placebo-controlled trial found that adults with poor sleep quality showed improvements in both sleep and mood after supplementing with magnesium daily for two weeks. If you’re not getting enough through your diet (leafy greens, nuts, seeds, and legumes are the richest sources), a supplement in the glycinate or bisglycinate form is gentler on the stomach and better absorbed than cheaper oxide forms.
Reduce Overnight Disruptions
Every time you wake up during the night, even briefly, your brain has to restart its progression through the lighter stages before reaching deep or REM sleep again. This means frequent awakenings can disproportionately eat into your restorative stages even if your total time in bed looks normal.
Common culprits include a full bladder (stop drinking fluids about 90 minutes before bed), noise (a white noise machine or earplugs can mask intermittent sounds), and a sleeping partner’s movement (consider a mattress with better motion isolation). Pets on the bed are another frequent source of micro-awakenings that most people underestimate.
What Realistic Improvement Looks Like
If you’re currently getting, say, 5 percent deep sleep and 12 percent REM, you’re unlikely to double those numbers overnight. Most people see incremental gains of a few percentage points over several weeks as they stack these habits together. A wearable tracker can help you spot trends, but don’t obsess over nightly readings, which vary naturally based on stress, illness, and dozens of other factors. The better metric is how you feel: less morning grogginess, better emotional regulation, sharper memory, and more physical energy are all signs your deep and REM sleep are improving.
The changes with the biggest payoff are the simplest ones: a consistent wake time, a cool bedroom, regular exercise, and cutting alcohol close to bedtime. Layer in glycine or magnesium if those basics are already in place and you still feel there’s room to improve.