For most people, sleeping on the left side is the better choice. It reduces acid reflux, supports digestion, and keeps your airway more open during sleep. But the answer changes depending on your specific health situation. People with heart failure, for example, often feel more comfortable on the right. Here’s what the evidence says for each scenario so you can pick the best position for your body.
Left Side for Acid Reflux and Digestion
Your stomach sits slightly to the left side of your body, and its connection to the esophagus (the tube from your throat) enters at the top right of the stomach. When you lie on your left side, gravity keeps the contents of your stomach pooled below that opening, making it harder for acid to flow back up. Flip to the right side, and that junction essentially sits below the pool of stomach acid, giving it an easy path upward. Research from Amsterdam UMC confirmed this anatomical advantage: sleeping on the left side significantly reduces acid reflux episodes.
Digestion speed, though, tells a different story. A study in The Journal of Physiology found that the stomach empties nearly twice as fast when you lie on the right side compared to the left. After 10 minutes, subjects lying on their right retained only about 215 milliliters of a test solution, while left-side sleepers still had 431 milliliters in their stomachs. If you’ve eaten a large meal and just want it to move through, lying briefly on your right side can help. But if you’re prone to heartburn or reflux, the left side wins overall, especially at bedtime.
Right Side for Heart Failure
If you have heart failure, the left side may not feel great. Many people with this condition notice increased shortness of breath when lying on their left, likely because the position shifts the heart slightly and increases pressure on it. The American Heart Association has noted that people with heart failure often naturally prefer their right side for this reason. If you have a healthy heart, this isn’t a concern, but for anyone managing heart failure, the right side is typically more comfortable and may help with breathing during sleep.
Either Side Beats Your Back for Snoring and Sleep Apnea
When you sleep on your back, gravity pulls the tongue and soft tissues in the throat backward, narrowing your airway. This is why back sleeping is the worst position for snoring and obstructive sleep apnea. Switching to either side opens the airway significantly. A Cochrane review of positional therapy found that side sleeping reduced breathing disruptions by an average of about 7 events per hour compared to back sleeping. For people whose apnea is position-dependent (meaning it’s mostly a problem on their back), simply staying on their side can cut the number of breathing pauses by 50% or more.
Brain Waste Clearance During Sleep
Your brain has its own waste-removal system that ramps up during sleep, flushing out metabolic byproducts through cerebrospinal fluid. Research published in Brain Sciences found that this system works most efficiently when sleeping on the right side, with greater fluid clearance compared to sleeping on the back or stomach. This is an area where the science is still developing, but the finding is notable: side sleeping in general supports brain cleanup, and the right side may have a slight edge.
Protecting Your Shoulders
The downside of side sleeping is shoulder pressure. When you lie on one side, your body weight compresses the shoulder underneath you for hours. Research published in PMC found that side sleeping produces the highest pressure in the shoulder joint compared to back or stomach sleeping. Over time, this sustained compression can reduce blood flow to the rotator cuff tendons and contribute to degenerative changes, especially as you age and move less during the night.
The practical fix is to alternate sides rather than always sleeping on the same one. If you already have shoulder pain on one side, sleep on the opposite side or on your back until it improves. A mattress with enough give to let your shoulder sink in slightly, rather than pressing against a firm surface, also helps reduce that compression.
Sleep Wrinkles Are Real
About 65% of people sleep on their side, making it the most common position. But a study in the Aesthetic Surgery Journal found that pressing your face against a pillow night after night creates compression and shear forces that gradually form wrinkles. The forehead, cheeks, and lips are the most affected areas. These “sleep wrinkles” are distinct from expression lines and develop asymmetrically, typically worse on whichever side you favor. Sleeping on your back eliminates this entirely, but if you’re committed to side sleeping, a silk pillowcase reduces friction and some of that distortion.
How to Make Side Sleeping More Comfortable
Whichever side you choose, alignment matters. Without support, your top leg tends to fall forward during the night, twisting your lower back and pulling your spine out of its natural position. Placing a pillow between your knees keeps your hips stacked and your pelvis level. The pillow should be thick enough to keep your knees roughly hip-width apart but not so thick that it forces your legs apart unnaturally.
If you shift around a lot during sleep, a full-length body pillow works better than a standard pillow because it supports both your knees and ankles throughout the night. Your head pillow matters too: it should fill the gap between your ear and the mattress so your neck stays in line with your spine rather than bending up or down.
Choosing Your Best Side
Left side sleeping is the strongest general recommendation. It handles acid reflux, supports digestion at a comfortable pace, and works well for snoring and sleep apnea. Choose the right side if you have heart failure or if your left shoulder is bothering you. For brain health, the right side may have a slight advantage, though both sides are far better than sleeping on your back or stomach for most purposes.
If none of these conditions apply to you, the most honest answer is: sleep on whichever side feels comfortable, and try to alternate. Your body already does this naturally during the night. The biggest gains come not from obsessing over left versus right, but from staying off your back if you snore, keeping your spine aligned with a knee pillow, and giving your shoulders a break by switching sides.