Side sleeping is the best position for most people, offering advantages for breathing, digestion, and brain health. More than 60% of adults already sleep this way naturally. But the “best” position also depends on what your body needs: whether you’re managing back pain, acid reflux, sleep apnea, or pregnancy changes the calculus. Here’s what each position does well and where it falls short.
Why Side Sleeping Works for Most People
Side sleeping checks the most boxes. It keeps your airway open (reducing snoring and sleep apnea episodes), supports digestion, and allows your brain’s waste-clearance system to work at peak efficiency. Research published in the Journal of Neuroscience found that the brain clears metabolic waste, including proteins linked to Alzheimer’s disease, most efficiently when the body is in a lateral (side) position compared to sleeping on the back or stomach.
To get the most out of side sleeping, place a pillow between your knees. This keeps your hips, pelvis, and spine aligned and prevents your top leg from pulling your lower back out of position. Drawing your legs up slightly toward your chest can take additional pressure off the spine. A full-length body pillow works well if you tend to shift around at night.
Which side matters depending on your situation. Sleeping on your left side eases acid reflux because gravity and the natural angle between your stomach and esophagus keep acid from creeping upward. Sleeping on your right side is gentler on the heart. Studies using heart monitoring found that right-side sleeping keeps the heart in a more stable position, cushioned by the tissue between the lungs, while left-side sleeping can subtly shift it. For people with heart failure, who often feel short of breath lying on their left side, the right side is typically more comfortable.
Side Sleeping and Shoulder Pain
The one clear downside of side sleeping is shoulder pressure. Gravity pulls the shoulder downward into the mattress, which can aggravate rotator cuff issues or create new soreness over time. If you have a painful shoulder, sleep with that shoulder facing up rather than pressed into the bed. Use a pillow to support the upper arm in a straight, neutral position so it doesn’t droop across your body.
Switching sides throughout the night helps distribute pressure. If you consistently wake with shoulder stiffness on the side you slept on, a softer or more conforming mattress may reduce the problem by letting your shoulder sink in rather than bearing all your weight on a hard surface.
Back Sleeping: Best for Spinal Alignment
Sleeping on your back distributes your body weight evenly and keeps your head, neck, and spine in a neutral line without any twisting or bending. It’s the position least likely to cause neck or shoulder pain, and it prevents the facial compression that side and stomach sleeping can cause over years.
The main drawback is your airway. When you lie flat on your back, gravity pulls the tongue and soft tissues toward the back of the throat, which narrows the airway. For people with obstructive sleep apnea, this is a serious concern. Polysomnography data shows that the severity of breathing interruptions can double in the supine position compared to sleeping on the side. The duration of each event, the drop in oxygen levels, and the resulting heart rate swings are all significantly worse when sleeping face-up. If you snore heavily or have been diagnosed with sleep apnea, back sleeping is generally the position to avoid.
If you do sleep on your back, place a pillow under your knees. This relaxes your lower back muscles and maintains the natural curve of your lumbar spine. A small rolled towel tucked under your waist can provide additional support if you still feel a gap between your lower back and the mattress.
Stomach Sleeping: The Position to Reconsider
Stomach sleeping is the hardest position on your body. Because you have to turn your head to one side to breathe, your cervical spine spends hours in a rotated position. This creates asymmetric tension in your neck muscles and can lead to stiffness, soreness, and nerve irritation over time. The Hospital for Special Surgery calls it the worst option for neck pain because it makes maintaining a neutral spine impossible.
Stomach sleeping also creates problems downstream. Tucking your arm under your pillow, a common habit for stomach sleepers, compresses the shoulder joint and sets the stage for rotator cuff issues. Your lower back tends to sag into the mattress, which hyperextends the lumbar spine.
If you can’t break the habit, a thin pillow (or no pillow) under your head reduces the angle of neck rotation. Placing a flat pillow under your pelvis can help prevent your lower back from arching too deeply. But if you regularly wake up with neck or back pain, switching to your side is worth the adjustment period.
Best Positions for Specific Conditions
Acid Reflux and GERD
Sleep on your left side. The stomach sits to the left of the esophagus, so this position uses gravity to keep stomach acid where it belongs. Right-side sleeping and back sleeping both allow acid to pool near the junction between the stomach and esophagus, making nighttime reflux worse. Elevating your head with a wedge pillow adds another layer of protection by tilting the entire upper body, not just the neck.
Lower Back Pain
Both side and back sleeping work well with the right support. Side sleepers should bend their knees slightly and use a pillow between them. Back sleepers should place a pillow under the knees to flatten the lumbar curve and relieve pressure on the spine. Stomach sleeping tends to make back pain worse because it forces the lower spine into extension for hours.
Sleep Apnea and Snoring
Side sleeping is the first-line positional recommendation. Avoiding the supine position alone can cut the frequency and severity of apnea events roughly in half for people whose breathing interruptions are position-dependent. Some people use positional therapy devices (like a wearable that vibrates when you roll onto your back) to maintain side sleeping throughout the night.
Pregnancy
The American College of Obstetricians and Gynecologists recommends side sleeping during the second and third trimesters, with one or both knees bent. A pillow between the knees and another under the belly helps support the weight of the uterus and reduces strain on the lower back. Left-side sleeping is often suggested because it keeps pressure off the large vein that returns blood from the lower body to the heart, improving circulation to the placenta.
Glaucoma and Eye Pressure
Lying flat increases pressure inside the eye, and sleeping consistently on one side can raise pressure in the eye closest to the pillow. A 2010 study found that people with glaucoma who slept on a 30-degree wedge pillow had significantly lower eye pressure overnight compared to lying flat. If you have glaucoma, alternating sides and elevating your head may help.
How to Change Your Sleep Position
Your body naturally gravitates toward familiar positions during sleep, so changing takes deliberate effort. Pillows are your best tool: a body pillow prevents you from rolling onto your stomach, a pillow between the knees locks in a side position, and a wedge pillow discourages rolling from back to side if you’re trying to stay supine. Most people adjust within two to four weeks if they’re consistent with pillow placement.
Your mattress matters too. Side sleepers generally need a softer surface that lets the shoulder and hip sink in without creating pressure points. Back sleepers do better on a medium-firm surface that supports the natural curve of the spine without letting the hips sag. If you’re waking up sore every morning regardless of position, the mattress may be the bigger issue than which way you’re facing.