For most people, sleeping on the left side offers the widest range of health benefits, from better digestion to faster acid clearance in the esophagus. That said, the best side depends partly on your specific health situation. People with heart failure, for example, often do better on their right side. Here’s what the evidence says about each position and who benefits most from which.
Why Left-Side Sleeping Gets the Most Recommendations
The left side wins for digestion, and the reason is simple anatomy. Your stomach naturally curves to the left, so when you lie on that side, gravity keeps stomach acid pooled away from the opening to your esophagus. A study of 57 people with chronic heartburn found that while the number of acid reflux episodes was similar regardless of position, acid cleared from the esophagus significantly faster when participants slept on their left side compared to their back or right side. If you deal with heartburn or GERD, this one change can make a noticeable difference in how you feel overnight and in the morning.
Your digestive tract also benefits beyond the stomach. The valve connecting your small intestine to your large intestine sits in your lower right abdomen. When you sleep on your left side, gravity helps move waste through the natural path of the colon: up the right side (ascending colon), across the middle (transverse colon), and down the left side (descending colon) toward the exit. This is one reason many people find that left-side sleeping encourages a more regular morning bowel movement.
Brain Waste Clearance During Sleep
Your brain has its own waste-removal system that works primarily while you sleep, flushing out metabolic byproducts including proteins linked to Alzheimer’s disease. Research published in the Journal of Neuroscience found that this cleaning process was most efficient when sleeping on the side (lateral position) compared to sleeping on the back or stomach. In the study, sleeping face-down showed the slowest waste clearance, with more fluid retained in the brain rather than being flushed out. Side sleeping, and particularly right-side sleeping in the study’s measurements, showed the most pronounced “loss” of waste material, meaning the brain was doing a better job of taking out the trash.
This research was conducted in animal models, so the exact numbers don’t translate directly to humans. But it adds to a growing picture of why side sleeping, which adults already do about 54% of the night on average, may be the position our bodies naturally favor for good reason.
When Right-Side Sleeping Is Better
If you have heart failure, sleeping on your left side can worsen shortness of breath. The heart sits slightly left of center in the chest, and lying on that side shifts its weight and changes how blood flows back to it. Many people with heart failure instinctively prefer their right side because breathing feels easier there. This is one of the clearest cases where right beats left.
For people without heart conditions, right-side sleeping is still a perfectly healthy option. It simply doesn’t offer the same digestive advantages as the left side. If heartburn and digestion aren’t concerns for you, either side works well.
Side Sleeping and Sleep Apnea
If you snore or have obstructive sleep apnea, side sleeping on either side is dramatically better than sleeping on your back. When you lie face-up, gravity pulls the tongue and soft tissues toward the back of the throat, partially blocking the airway. A meta-analysis found that switching from back sleeping to side sleeping reduced the severity of sleep apnea events by about 54%. For people with mild to moderate sleep apnea, positional changes alone can sometimes bring symptoms under control.
Sleep Position During Pregnancy
Pregnant women often hear they must sleep exclusively on their left side, but that advice is outdated. The American College of Obstetricians and Gynecologists clarifies that either side is fine throughout pregnancy. The key thing to avoid is sleeping flat on your back during the later months, because the weight of the growing uterus compresses major blood vessels that supply the placenta.
If you wake up on your back during your second or third trimester, there’s no need to panic. Just roll to whichever side is comfortable. Left-side sleeping does slightly optimize blood flow to the uterus, but the practical difference between left and right is small enough that comfort should guide your choice.
How to Make Side Sleeping More Comfortable
Side sleeping only works well if your spine stays aligned. When your body sinks unevenly into the mattress or your head tilts at an angle, you can wake up with neck, shoulder, or hip pain. A few adjustments make a big difference.
Your pillow height matters more than you might think. It needs to fill the gap between your ear and the mattress so your neck stays straight, not tilted up or down. Most side sleepers need a thicker pillow than back sleepers do. If you frequently wake up with a stiff neck, your pillow is likely the wrong height.
Placing a pillow between your knees is the single most effective change for lower back comfort. According to the Mayo Clinic, drawing your legs slightly toward your chest and putting a pillow between them helps align your spine, pelvis, and hips while taking pressure off the lower back. A full-length body pillow works too, especially if you tend to roll forward onto your stomach during the night.
Shoulder pain is the most common complaint among side sleepers. Avoid tucking your bottom arm under your pillow or body. Instead, keep both arms in front of you or hug a pillow to keep your top shoulder from rolling forward. If one shoulder consistently bothers you, try switching to the other side.
Choosing Your Best Side
- Left side is the default best choice for most adults, especially if you experience heartburn, bloating, or irregular digestion.
- Right side is preferable if you have heart failure or find left-side sleeping uncomfortable due to shoulder or hip issues on that side.
- Either side works well for sleep apnea, pregnancy, and brain health. The biggest gains come from avoiding back and stomach sleeping, not from choosing one side over the other.
Most people naturally shift between sides several times per night, and that’s completely normal. If you want to train yourself toward one side, placing a body pillow behind your back can prevent you from rolling over. Starting the night on your preferred side also increases the total time you spend there, even if you move later.