by Quick answer: Left-side sleeping is generally recommended for most adults, it eases acid reflux, supports digestion by following the natural curve of the stomach, and improves circulation during pregnancy. That said, the best side depends on your specific condition. Side sleeping overall promotes spinal alignment better than stomach sleeping for most people.
By the MattressNut editorial team · Chiropractor-reviewed · Updated June 2026
Left Side vs. Right Side: What Each Does for Your Body
The difference between left and right isn't trivial, anatomy makes one side meaningfully better for certain conditions.
Left-Side Sleeping: Benefits
- Acid reflux and GERD: The stomach sits to the left of the esophagus. Lying on the left keeps stomach acid below the lower esophageal sphincter, reducing nighttime reflux symptoms. Right-side sleeping does the opposite, it relaxes the sphincter and allows acid to rise more easily.
- Pregnancy: After the first trimester, left-side sleeping is widely recommended by OB-GYNs. It reduces pressure on the inferior vena cava (the large vein running along the right side of the spine), improving blood flow to the heart, kidneys, and fetus. Always confirm position recommendations with your doctor during pregnancy.
- Digestion: The ileocecal valve, which separates the small and large intestine, sits in the lower right abdomen. Left-side sleeping may support the natural movement of waste from the small intestine into the large intestine, aided by gravity.
- Heart: For most people, left-side sleeping places no added strain on the heart. Some people with certain cardiac conditions report more comfort on the right side, ask your cardiologist if you have a diagnosed heart condition.
Right-Side Sleeping: When It Makes Sense
- Heart conditions: Some research suggests right-side sleeping may reduce mechanical pressure on the heart for people with heart failure, though this area is still studied. Speak with your doctor rather than self-prescribing position changes.
- Comfort: If you've slept on your right side for years without symptoms, it works for you. Pain, numbness, or waking up exhausted are the signals to reassess, not side preference alone.
- Shoulder pain: If your left shoulder is injured or painful, right-side sleeping removes pressure from it. The reverse applies too.
Best Side to Sleep On By Condition
Acid Reflux and GERD
Left-side sleeping is backed by gastroenterology research as the better position for nighttime reflux. The geometry of the stomach means acid pools away from the esophagus on the left. If you frequently wake with burning or an acid taste, try switching to your left side and elevating your head 4–6 inches. Wedge pillows work better than stacking standard pillows, which tend to shift during the night.
Pregnancy
The left side is the standard clinical recommendation from the second trimester onward. It keeps the uterus off the aorta and vena cava, supporting fetal blood flow. A full-length body pillow tucked between the knees and under the belly can make left-side sleeping sustainable through the third trimester. If you roll onto your back during sleep, don't stress, the recommendation is to start on the left, not to achieve perfect overnight compliance.
Snoring and Sleep Apnea
Back sleeping allows the tongue and soft palate to fall toward the throat, narrowing the airway. Side sleeping, left or right, keeps the airway more open. If you snore or have been diagnosed with sleep apnea, side sleeping is a consistent recommendation alongside any prescribed treatment like CPAP. Left-side sleeping is marginally preferred in some clinical settings, but either side is better than the back.
Back Pain
Side sleeping with a pillow between the knees is a common chiropractor recommendation for lower back pain. The pillow prevents the top hip from rotating forward, which pulls the lumbar spine out of neutral alignment. Without it, a 6–8 hour twist adds up. Our chiropractor reviewers consistently flag this as the most overlooked adjustment side sleepers can make, it costs nothing and changes how the lower back feels in the morning.
Heart Conditions
The evidence here is genuinely mixed. Left-side sleeping is fine for most people. For those with diagnosed heart failure or certain arrhythmias, some clinicians recommend the right side to reduce mechanical stretch on the heart. This is a case where a doctor's guidance matters more than general advice.
Side-Sleeping Posture and the Right Mattress and Pillow Setup
Position choice matters less if your setup works against you.
Pillow Height
Your head should be level with your spine when viewed from the front, not tilted up toward the ceiling or dropped toward the mattress. Side sleepers generally need a thicker, firmer pillow than back sleepers. A pillow too thin creates a lateral neck bend held for hours; one too thick pushes the neck the other way. Fill adjustability (shredded memory foam or latex) lets you dial in the right height.
Mattress Firmness for Side Sleepers
Side sleeping concentrates body weight on the shoulder and hip. A mattress that's too firm pushes back against those pressure points and forces the spine into a sideways curve. Medium-soft to medium firmness generally works best for side sleepers, enough give to let the shoulder and hip sink slightly, while still supporting the waist so it doesn't collapse.
Heavier side sleepers often do better toward the medium end to avoid sinking too deep, which also misaligns the spine. Lighter sleepers may prefer the softer end of medium.
We've tested dozens of mattresses for pressure relief at the shoulder and hip in our Sleep Lab. For side sleepers who want a well-documented pressure-relief option, our full Saatva review covers how its three firmness options perform for different body types and sleep positions.
Knee Pillow
A regular pillow folded in half or a dedicated knee pillow placed between the knees keeps hips stacked and prevents lumbar rotation. This is especially useful for side sleepers with hip bursitis or sciatica-type symptoms.
What to Know
| Factor | Detail |
|---|---|
| Left-side sleeping | Generally preferred for acid reflux, GERD, and pregnancy. May support digestion through natural gastric geometry. |
| Right-side sleeping | May suit people with certain cardiac conditions; also a practical choice when the left shoulder is injured. |
| Side sleeping overall | Better than stomach sleeping for spinal alignment. A pillow between the knees prevents hip rotation and lumbar strain. |
| Mattress firmness | Medium-soft to medium for most side sleepers, allows shoulder and hip to sink without spine collapse. |
| Pillow height | Should keep the head level with the spine. Too thin or too thick both create neck strain over a full night. |
Frequently Asked Questions
Is it better to sleep on your left or right side?
Left-side sleeping is generally favored for acid reflux, GERD, and pregnancy because of how the stomach and major blood vessels are positioned anatomically. For most healthy adults, either side is fine as long as the spine stays neutral and sleep is comfortable. If you have a specific condition, check with a doctor.
Does sleeping on your side cause shoulder pain?
It can, particularly if your mattress is too firm. A firm surface doesn't allow the shoulder to sink, which creates pressure at the shoulder joint and can cause pain or numbness down the arm. Medium-soft mattresses and confirming your pillow height is correct resolves most side-sleeping shoulder discomfort. If pain persists, see a doctor to rule out rotator cuff issues.
Is left-side sleeping good for the heart?
For most people, yes, left-side sleeping doesn't stress the heart and may even improve circulation by keeping pressure off the vena cava. For people with diagnosed heart failure or certain arrhythmias, some clinicians prefer right-side sleeping. If you have a heart condition, ask your cardiologist about the best sleep position for your specific diagnosis.
Can sleeping on your side reduce snoring?
Yes. Back sleeping is the main position that worsens snoring because gravity pulls the tongue and soft tissues toward the airway. Side sleeping, left or right, keeps the airway more open. It's one of the first adjustments recommended for mild snoring. For diagnosed sleep apnea, side sleeping complements CPAP treatment but doesn't replace it.
What pillow is best for side sleepers?
Side sleepers need a pillow thick enough to fill the space between the ear and shoulder, typically thicker than what back sleepers use. Adjustable fill pillows (shredded latex or memory foam) are practical because you can add or remove fill until your head sits level with your spine. Pillow loft that's too low causes a lateral neck tilt held for hours, which leads to morning stiffness.
Should pregnant women sleep on the left side the whole night?
Left-side sleeping is the standard recommendation from the second trimester, primarily because it avoids compressing the vena cava and supports fetal circulation. Perfect compliance through the night isn't realistic, rolling to the right or briefly onto the back doesn't cause harm. The goal is to start on the left and return to it when you wake. A body pillow helps maintain the position longer. Always follow your OB-GYN's specific guidance.
The Bottom Line
Left-side sleeping is the generally recommended starting point: it suits acid reflux, GERD, pregnancy, and digestion based on how the stomach and major vessels are positioned. Right-side sleeping works for most healthy adults and has a possible edge for certain heart conditions. Whichever side you choose, the mechanics matter, a pillow between the knees, correct pillow height, and a medium-soft mattress that lets the shoulder and hip decompress will determine how you actually feel in the morning.
Bottom line: Side sleeping suits most people, left is the default recommendation for reflux and pregnancy, and the right setup (pillow height, knee pillow, mattress firmness) makes as much difference as which side you pick.
Related: our full Saatva mattress review.