Sleeping on your left side is one of the most commonly recommended positions for digestive comfort, and training yourself to stay there through the night is surprisingly straightforward once you set up your bed correctly. The key is using pillows strategically and creating a physical environment that discourages you from rolling onto your back or right side.
Why Left Side Sleeping Matters
The main reason left side sleeping gets so much attention comes down to anatomy. Your stomach naturally curves to the left, sitting below the junction where it meets the esophagus. When you sleep on your left side, gravity keeps stomach acid pooled at the bottom of the stomach, well away from that opening. Roll to the right, and the acid sloshes toward the esophagus, making reflux more likely.
A study published in The American Journal of Gastroenterology used real-time monitoring of sleep position alongside esophageal pH levels and found that left side sleeping reduced nighttime reflux more effectively than sleeping on the back or right side. Up to 80% of people with GERD experience symptoms at night, so position alone can meaningfully improve sleep quality. The frequency of reflux events may not change dramatically between positions, but the severity and duration of acid exposure drops on the left side.
Beyond digestion, sleeping on your side (either side) appears to help your brain’s waste clearance system work more efficiently. A neuroscience study using imaging tracers found that the brain’s fluid exchange, which flushes out metabolic waste including proteins linked to Alzheimer’s, was most efficient in the lateral (side) position compared to sleeping face up or face down. This waste clearance happens primarily during sleep, making your sleeping posture a surprisingly relevant factor.
Who Benefits Most
If you deal with heartburn, GERD, or frequent acid reflux, left side sleeping is one of the simplest changes you can make. Johns Hopkins Medicine specifically recommends flipping to the left side to reduce nighttime heartburn, noting that the right side can make symptoms worse.
People who snore or have mild sleep apnea also benefit from side sleeping in general, as it helps keep the airway open compared to lying on your back. Left or right doesn’t matter as much here; what matters is getting off your back.
For young, healthy people without specific conditions, sleep position matters less than you might think. Hopkins notes that comfort should be your guide if you don’t have reflux, apnea, or other issues driving you toward a particular position. The benefits of left side sleeping become more pronounced as you age or develop conditions where gravity and anatomy play a role in symptom management.
When Left Side Sleeping Isn’t Ideal
People with heart failure often find that sleeping on the left side worsens shortness of breath. The American Heart Association notes that many heart failure patients prefer sleeping on their right side for this reason. If you have a heart condition and notice breathing difficulty on the left, the right side is a better choice.
Shoulder problems are the other common obstacle. Sleeping on your left side puts sustained pressure on the left shoulder, and Cleveland Clinic notes that people with shoulder impingement or rotator cuff issues experience more pain when lying on the affected side. If your left shoulder is already sore or injured, forcing yourself to sleep on it will make things worse. The same applies to the left hip: if you have bursitis or joint pain on that side, the pressure from side sleeping can aggravate it overnight.
A Note on Pregnancy
You may have heard that pregnant women should always sleep on the left side to avoid compressing a major vein called the inferior vena cava. This advice is widespread but overstated. Research published in the Journal of Obstetrics and Gynaecology Canada found that while lying flat on the back can cause lightheadedness in some pregnant women, only 2% to 4% of those who become symptomatic have significant blood vessel compression. Even in that small group, there was no evidence of harm to the fetus. The researchers concluded that the blanket advice to sleep exclusively on the left side isn’t well supported. If lying on your back feels uncomfortable during pregnancy, shifting to either side is reasonable, but there’s no need to stress about maintaining one exact position all night.
How to Train Yourself to Stay on Your Left Side
Most people shift positions 10 to 30 times per night, so the goal isn’t to lock yourself in place. It’s to make the left side your default, the position you start in and return to naturally.
Use a body pillow or back barrier. Place a firm pillow or rolled-up blanket along your back after you settle onto your left side. This creates a physical block that makes rolling onto your back feel uncomfortable enough that your body adjusts without fully waking you. A full-length body pillow between your knees and arms also stabilizes your torso and reduces the urge to rotate.
Try the tennis ball method. Tape or sew a tennis ball (or a similar small, firm object) into the back of a snug sleep shirt, or into a pocket on the right side. When you roll onto your back or right side, the discomfort nudges you back to the left. This technique is commonly used in positional therapy for sleep apnea and works for retraining side preference too. Most people only need it for a few weeks before the habit sticks.
Position your bed intentionally. If your bed is against a wall, sleep with your right side facing the wall. The proximity of the wall discourages rolling that direction. If you have a nightstand with a lamp or phone charger, put it on the left side of the bed so you naturally orient toward it when settling in.
Elevate slightly if reflux is the goal. Combine left side sleeping with a wedge pillow or a few extra inches of elevation under your head and upper torso. This adds a second layer of gravity working against acid reflux and can make a noticeable difference for people whose symptoms aren’t fully controlled by position alone.
Pillow Setup for Comfort
The biggest reason people abandon side sleeping is shoulder and neck pain from poor alignment. Your spine should form a straight line from your head through your hips when viewed from behind. This requires a pillow thick enough to fill the gap between your ear and the mattress without tilting your head up or letting it drop down. For most side sleepers, this means a medium-firm pillow that’s noticeably thicker than what a back sleeper would use.
Place a second pillow or folded towel between your knees. Without it, the weight of your top leg pulls your pelvis forward, twisting your lower spine. A knee pillow keeps your hips stacked and reduces pressure on both the hip joint and lower back. If you tend to hug a pillow with your arms, that also helps keep your top shoulder from collapsing forward, which is what causes the shoulder ache many side sleepers complain about.
Your mattress matters too. A mattress that’s too firm creates pressure points at the shoulder and hip, the two widest parts of your body when lying on your side. A medium or medium-soft mattress lets those areas sink in slightly while still supporting your waist. If replacing your mattress isn’t an option, a 2- to 3-inch foam topper can soften the surface enough to reduce pressure.
How Long It Takes to Adjust
If you’re a lifelong back or right side sleeper, expect an adjustment period of one to three weeks. The first few nights often feel awkward, and you’ll wake up on your back or stomach more often than not. This is normal. The physical barriers (back pillow, tennis ball) do most of the work during this phase. By the second week, most people find they’re starting the night on the left and returning to it after waking briefly. By three to four weeks, the position typically feels natural enough that you no longer need the props.
Don’t fight it if you wake up in a different position occasionally. The goal is to spend the majority of your sleep time on the left side, not every single minute. Even partial compliance reduces reflux exposure and provides the other positional benefits throughout the night.