Deep sleep, the stage when your heart rate and breathing slow to their lowest levels, typically makes up 10% to 20% of your total sleep time. It’s the phase when your body repairs tissue and releases essential hormones. Several practical habits can protect and increase the amount of deep sleep you get each night, from how you time your light exposure to what you do in the hours before bed.
What Happens During Deep Sleep
During deep sleep (also called slow-wave sleep), your brain produces large, slow electrical waves. Your blood pressure drops, your muscles fully relax, and your body shifts into recovery mode. Growth hormone surges, tissues regenerate, and your immune system does some of its most important work. If someone tried to wake you during this stage, you’d feel groggy and disoriented.
Most of your deep sleep happens in the first half of the night, with lighter sleep and dreaming stages dominating the second half. This matters because anything that disrupts early-night sleep, like alcohol or a too-warm room, tends to cut into deep sleep disproportionately. It’s also worth knowing that deep sleep naturally declines with age. Children and teenagers get the most, while adults see a gradual decrease that levels off around the 70s.
Get Sunlight Early in the Day
Morning light is one of the simplest tools for better deep sleep at night. Sunlight in the first few hours after waking tells your internal clock what time it is, strengthening the circadian rhythm that governs when you feel alert and when you feel sleepy. Afternoon light reinforces that signal further. Even 30 minutes outside makes a measurable difference.
There’s a secondary benefit: the stronger your daytime light exposure, the less artificial light at night can throw off your system. Your body essentially becomes more resilient to the screens and indoor lighting that would otherwise delay sleep onset.
Exercise at the Right Time
Physical activity consistently improves deep sleep, but timing matters. Evening exercise has been shown to help people fall asleep faster and spend more time in slow-wave sleep. The key caveat is intensity: high-intensity workouts like interval training done less than an hour before bed can backfire, making it harder to fall asleep and reducing overall sleep quality.
A reasonable guideline is to finish any vigorous exercise at least two hours before you plan to get into bed. Moderate activity, like a walk or gentle yoga, is generally fine closer to bedtime.
Cool Your Bedroom Down
Your core body temperature needs to drop slightly for you to enter and stay in deep sleep. A bedroom kept between 60 and 67°F (15 to 19°C) supports this process. Thermoregulation plays a direct role in maintaining the slow-wave sleep stages, so a room that’s too warm doesn’t just make you uncomfortable. It can physically prevent your body from reaching the deepest phase of sleep.
If you can’t control your room temperature precisely, lighter bedding, breathable fabrics, and a fan can help bridge the gap.
Take a Warm Shower or Bath Before Bed
This one sounds counterintuitive, but warming your body before sleep actually helps it cool down faster afterward. A warm shower or bath taken one to two hours before bed increases blood flow to your hands and feet, which accelerates heat loss from your core. That drop in core temperature is exactly what your body needs to transition into deep sleep.
A systematic review of the research found that even 10 minutes of warm water exposure was enough to improve sleep, primarily by helping people fall asleep more quickly. The timing window of one to two hours before bed appears to be the sweet spot.
Limit Blue Light Before Bed
Screens emit blue-spectrum light that suppresses melatonin, the hormone that signals your brain it’s time to sleep. In a controlled study of healthy young men, one hour of blue light exposure before bed significantly reduced the proportion of deep sleep compared to both incandescent light and blue-light-blocking glasses. The effect was strong enough to reach statistical significance even in a small group.
Dimming screens, switching devices to night mode, or wearing blue-light-blocking glasses in the hour before bed can all help preserve your deep sleep. Better yet, stepping away from screens entirely for that last hour gives your brain the clearest signal that nighttime has arrived.
Watch What You Eat and Drink
Alcohol is one of the most common deep sleep disruptors. It acts on the same brain receptors as some insomnia medications, so it can initially promote slow-wave sleep in the first half of the night. But this comes at a cost. As your body metabolizes the alcohol, rebound effects kick in during the second half of the night, fragmenting sleep and suppressing REM stages. The net result is lighter, less restorative sleep overall, even if you felt like you fell asleep quickly.
On the food side, a few options may support sleep. Tart cherry juice is a natural source of melatonin. Complex carbohydrates like whole-wheat toast or oatmeal trigger the release of serotonin, a precursor to melatonin, and digest quickly enough that they won’t keep your stomach working through the night. Eating these one to two hours before bed gives your body time to process them.
The Role of Magnesium
Magnesium is widely marketed as a sleep supplement, and many people report that it helps them relax before bed. The recommended daily intake ranges from about 310 to 420 mg for adults depending on age and sex. However, it’s worth noting that human studies haven’t conclusively proven magnesium supplements improve sleep. Most people can meet their magnesium needs through foods like nuts, seeds, leafy greens, and whole grains. If you’re considering a supplement, magnesium glycinate is one of the more easily absorbed forms and tends to be gentler on the stomach.
Consistency Ties It All Together
Individual habits matter, but their effects compound when they work together. Morning sunlight sets your circadian clock. Exercise builds sleep pressure throughout the day. A cool room and a warm pre-bed shower help your core temperature drop on schedule. Avoiding blue light and alcohol in the evening removes the most common obstacles. None of these require special equipment or major lifestyle changes, and stacking even a few of them can noticeably increase the time you spend in deep, restorative sleep.