Not everyone can sleep through the roar of traffic or someone else’s . If you can, consider that a small victory.
Researchers Kelly Sansom and Peter Eastwood from Murdoch University (Australia) explain what determines how deeply we sleep and whether we can change it.
Sleep isn’t a single state — it’s a cycle
First, remember that sleep isn’t one static state. It’s a cycle split into two main phases:
Non-REM (slow-wave) sleep.
REM (rapid eye movement) sleep.
Phase 1 — Non-REM (slow-wave) sleep
Non-REM makes up about 75–80 percent of total sleep time and consists of three stages:
Stage 1: dozing. This is the 1–5 minute transition from wakefulness to sleep, when muscles relax and the heart rate slows.
Stage 2: light sleep. Awareness fades, body temperature drops, and the brain produces bursts of activity.
Stage 3: deep sleep. This is the phase for physical recovery, collagen production, and growth hormone release.
Phase 2 — REM sleep
REM typically begins about 80–100 minutes after you fall asleep and accounts for roughly 20–25 percent of total sleep time. This phase is marked by rapid eye movements under the lids. The brain is highly active while the body becomes effectively paralyzed. Vivid dreaming happens mainly during REM.
Across the night people cycle through these stages 4–6 times. Getting full rest and physical recovery requires passing through every stage of the cycle.
You can’t stay in deep sleep all night
you might look completely inactive, but the brain never shuts off entirely, Sansom and Eastwood explain.
The sleeping brain shifts into a “standby” mode where it keeps monitoring the environment while filtering out many inputs. That filtering lets you suddenly wake up when you hear your name, a familiar voice, or a baby crying, because those sounds have a stronger effect on the brain than other noises.
During the second stage of non-REM sleep the brain sustains this standby mode with two types of brain waves:
- sleep spindles
- K-complexes
Sleep spindles are short bursts of electrical activity that help reduce how much external information the brain processes. K-complexes are sharp, high-amplitude waves that, like sleep spindles, help people sleep more soundly, Medical Xpress reports.
Deep sleep occurs in stage 3 of non-REM sleep, when the brain is least receptive to the outside world. Still, arousability — the chance of waking up — shifts as each sleep cycle progresses.
From a scientific perspective, that means you can’t remain in deep sleep for the entire night.
What else affects how well you sleep?
Here are four other factors that influence sleep quality:
- genetics
- stress
- light exposure
- various medical conditions
Genetics
Some genes influence sleep quality. For example, a common variant of the adenosine deaminase gene affects how efficiently the brain clears adenosine. Adenosine builds up during the day and produces sleep pressure. People who carry that gene variant spend more time in deep sleep and therefore wake up less often at night.
Recent studies show that sleep spindles are largely inherited. People with more sleep spindles tend to sleep better.
Stress
A stressful day can trigger intrusive thoughts and make falling and staying asleep difficult. That pattern, called sleep reactivity, often goes along with nighttime spikes in the stress hormone cortisol. Recent research finds sleep reactivity is a major contributor to insomnia.
Light
Light has a big impact on sleep quality. In one study, researchers compared healthy young adults who slept with a bedside lamp to those who slept without one. Participants who had the lamp slept less deeply and woke up more often.
Other researchers suggest that exposure to light at night can delay the body’s internal clock, making it harder to fall asleep.
How medical conditions affect sleep
Difficulty achieving deep sleep is often linked to certain medical conditions. For example, people with sleep apnea wake up more frequently and spend more time in light sleep. Some modern treatments can stabilize breathing and improve sleep quality.
Pain from conditions like endometriosis and irritable bowel syndrome also disrupts sleep. People commonly experience pain flare-ups at night, which makes deep sleep less likely.
How to sleep more soundly and deeply
To fall asleep faster and sleep more soundly, follow these simple rules:
- Avoid heavy dinners.
- Avoid coffee and alcohol before bed.
- Exercise or take a walk 2–3 hours before bedtime.
- Drink chamomile or mint tea, or have warm milk before bed.
- Take a warm bath or shower before bed.
- Go to bed and get up at the same time every day.
- Keep your bedroom quiet and well-ventilated; use blackout curtains.
No one sleeps entirely in deep sleep, Sansom and Eastwood summarize. Many factors shape how deep your sleep becomes. If you want better rest, creating a dark, quiet, low-stress bedroom is the right first step.
Photo: pexels.com
