For most people, sleeping on the left side offers the widest range of health benefits. It reduces acid reflux, supports digestion, and keeps your spine in a natural position. That said, the “best” side depends on your specific situation, whether you’re pregnant, dealing with heartburn, managing sleep apnea, or trying to protect a sore shoulder.
Why the Left Side Gets Top Marks
The left side wins for one simple anatomical reason: your stomach sits slightly to the left of your torso, and its opening to the esophagus sits at the top. When you lie on your left side, gravity keeps stomach acid pooled at the bottom of your stomach, away from that opening. Roll to your right, and acid can slosh up toward your throat more easily.
A 2022 study in The American Journal of Gastroenterology measured both sleep position and acid levels in the esophagus simultaneously, confirming that left-side sleeping reduces nighttime reflux more effectively than sleeping on your back or right side. If you deal with heartburn or GERD, this alone is reason enough to favor your left.
Left-Side Sleeping During Pregnancy
Pregnant women are commonly advised to sleep on their left side, and the reasoning is straightforward. As the uterus grows, lying flat on your back puts pressure on the inferior vena cava, the large vein that carries blood from your lower body back to your heart. That pressure can reduce blood flow to both you and the baby.
The left side is preferred over the right because it maximizes blood flow to the placenta and improves kidney function, which helps reduce swelling in the feet and ankles. It also takes pressure off the back and intestines, which tend to get increasingly compressed as pregnancy progresses. If you wake up on your back during the night, there’s no need to panic. Just roll back to your left and settle in.
How Side Sleeping Helps With Snoring and Sleep Apnea
If you snore or have obstructive sleep apnea, sleeping on your back is the worst position. Gravity pulls the tongue and soft tissues backward, narrowing or blocking the airway. Switching to either side makes a significant difference. A meta-analysis found that simply moving from back sleeping to a lateral position reduced breathing disruptions by about 54%. For mild to moderate sleep apnea, side sleeping (on either side) can be one of the most effective and simplest interventions.
Some people use a chest-worn positioning device or even a tennis ball sewn into the back of a sleep shirt to discourage rolling onto their back during the night. In one pilot study, a chest-worn belt cut the median number of breathing disruptions per hour from about 15 to under 7.
Your Brain’s Waste Removal System Prefers It Too
Your brain has a self-cleaning system that flushes out metabolic waste, including proteins linked to Alzheimer’s disease, while you sleep. Research published in the Journal of Neuroscience found that this waste clearance system works most efficiently when the body is in a lateral (side-lying) position compared to sleeping face down. Both side and back sleeping outperformed the prone position, but lateral sleeping showed the strongest and most consistent results. This aligns with the fact that most humans and animals naturally gravitate toward sleeping on their sides.
Protecting Your Shoulders and Spine
The main downside of side sleeping is that it concentrates your body weight through one shoulder and one hip for hours at a time. If you already have shoulder pain, sleeping on the affected side can aggravate it. The fix is straightforward: sleep on the opposite side, and prop your top arm on a folded blanket or pillow to take strain off the shoulder muscles.
Your spine also needs support in a side-lying position. Without it, your top leg tends to fall forward during the night, twisting your lower back and pulling your pelvis out of alignment. Placing a pillow between your knees keeps your hips stacked and your spine neutral, reducing the strain that builds up overnight from poor posture. A firm, medium-thickness pillow works better than a thin one that compresses flat by morning.
Your head pillow matters too. It should be thick enough to fill the gap between your ear and the mattress so your neck stays in line with your spine. Too thin and your head tilts down; too thick and it’s cranked upward. Either extreme can leave you with neck stiffness by morning.
The Case for Sleeping on Your Back
Back sleeping has one clear advantage over side sleeping: your face never presses into the pillow. Research published in the Aesthetic Surgery Journal found that compression, tension, and shear forces from pressing your face against a sleep surface cause wrinkles that worsen over time. These “sleep wrinkles” differ from expression lines because they’re caused by mechanical pressure, not muscle movement, which means treatments like Botox don’t help with them.
If you’re concerned about skin aging but can’t comfortably sleep on your back, switching sides during the night or using a silk pillowcase can reduce friction. Specialty pillows designed to cradle the face without compressing it are another option, though comfort varies.
Back sleeping also distributes your weight more evenly, which can help if you have pain in both shoulders or hips. But for people with reflux, snoring, sleep apnea, or pregnancy, back sleeping introduces problems that outweigh these benefits.
Choosing the Right Side for You
Here’s how to decide based on your primary concern:
- Acid reflux or GERD: Left side. The anatomy of your stomach makes this the clear winner.
- Pregnancy: Left side. It maximizes blood flow and eases pressure on the vena cava.
- Snoring or sleep apnea: Either side. The key is staying off your back.
- Shoulder pain: Whichever side is pain-free. Support the top arm with a pillow.
- Lower back pain: Either side with a pillow between your knees to keep your hips aligned.
- Wrinkle prevention: Back sleeping is best, though it’s a trade-off if you have other concerns.
If none of these conditions apply to you, the left side is a solid default. It supports digestion, brain waste clearance, and breathing, with no real downside beyond the normal wear that any side sleeper can manage with proper pillow support. Most people shift positions several times per night anyway, so starting on your left side and letting your body do its thing is a perfectly reasonable approach.