For most people, sleeping on the left side offers real advantages for digestion and circulation, though it’s not universally the best choice. The benefits are strongest for people dealing with acid reflux, pregnancy, or sleep apnea. For others, the differences between left and right side sleeping are modest, and comfort matters more than perfection.
Why Left-Side Sleeping Helps With Acid Reflux
The clearest benefit of left-side sleeping is for people who experience heartburn or gastroesophageal reflux. The reason is simple anatomy: your stomach sits slightly to the left of your esophagus. When you lie on your left side, your stomach falls below the junction where it connects to the esophagus, making it harder for acid to travel upward. Research from Amsterdam UMC also found that when acid does reach the esophagus during left-side sleeping, it drains back into the stomach more quickly.
Flip to your right side, and the geometry reverses. The stomach sits above or level with that junction, and acid pools closer to the opening of the esophagus. If you regularly wake up with heartburn or a sour taste in your mouth, switching to your left side is one of the simplest changes you can make.
Circulation Benefits During Pregnancy
Left-side sleeping is widely recommended during the second and third trimesters. As the uterus grows, it can compress the large vein (the inferior vena cava) that returns blood from your lower body to your heart. This compression is worst when you lie on your back, potentially causing dizziness, nausea, rapid heartbeat, and reduced blood flow to the placenta. Sleeping on the left side keeps the uterus off this vessel, improves blood return to the heart, and delivers more oxygen and nutrients to the baby. It also gives the liver, which sits on the right side, more space by keeping the uterus from pressing against it.
That said, right-side sleeping is a perfectly fine alternative when left-side sleeping gets uncomfortable. Major blood vessels remain relatively uncompressed on either side. The position to actively avoid in later pregnancy is flat on your back for prolonged stretches. If you wake up on your back, there’s no need to panic. Just roll to one side and settle back in.
Side Sleeping and Brain Waste Clearance
Your brain has its own waste-removal system that is most active during sleep, flushing out metabolic byproducts including proteins linked to Alzheimer’s disease. A study published in the Journal of Neuroscience tested how body position affects this process in animal models and found that side sleeping (lateral position) was the most efficient posture for clearing waste from the brain compared to sleeping face-down. Face-down sleeping, which most closely mimics an upright head posture, showed the slowest clearance and more “retention” of waste products.
This research didn’t find a meaningful difference between left and right side specifically. The takeaway is that side sleeping in general, which is already the most common human sleep position, appears to support the brain’s nightly cleanup process better than stomach sleeping.
Sleep Apnea Improves Off Your Back
If you snore heavily or have obstructive sleep apnea, sleeping position makes a measurable difference. Many people experience significantly more breathing interruptions while lying on their back because gravity pulls the tongue and soft tissues backward, narrowing the airway. A meta-analysis in the journal Thorax found that devices encouraging people to stay off their backs reduced breathing interruptions by an average of about 9 events per hour, roughly a 43% improvement. The percentage of time spent on the back dropped by 70%.
Again, this benefit applies to side sleeping in general, not specifically the left side. Rolling to either side opens the airway. If you’ve been told you snore mostly on your back, a body pillow or positional device that keeps you on your side can make a noticeable difference in sleep quality.
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 this leads many heart failure patients to prefer their right side. The left side places the heart closer to the chest wall and may shift how blood returns to an already struggling heart. If you have heart failure, your cardiologist can advise which position works best for your situation.
Left-side sleeping can also aggravate shoulder pain if you’re lying directly on that shoulder for hours. The same applies to hip pain. If you prefer side sleeping but wake up sore, placing a pillow between your knees helps align your hips and reduces strain on both joints. A supportive mattress that allows your shoulder and hip to sink in slightly, rather than pressing against a hard surface, also makes a difference.
Side Sleeping and Your Skin
One genuine downside of any side sleeping position is its effect on your skin over time. When your face presses against a pillow for hours each night, the repeated compression and friction can create wrinkles that look different from expression lines. These “sleep wrinkles” tend to appear as vertical or diagonal creases on the cheeks, around the eyes, and along the jawline, and they become more pronounced with age as the skin loses elasticity.
If this concerns you, a few strategies help. Silk or satin pillowcases reduce friction compared to cotton. You can also position your head so your temple rests on the pillow’s edge while the rest of your face, from cheekbone to chin, hovers above the surface rather than pressing into it. A silk sleep mask adds extra protection around the delicate eye area. Back sleeping eliminates the issue entirely, but for most people, the circulation and digestive benefits of side sleeping outweigh the cosmetic tradeoff.
Which Side Should You Actually Choose?
If you have acid reflux, left side. If you’re pregnant, left side when comfortable, right side when you need a change. If you have heart failure, right side. If you have sleep apnea or snore, either side is better than your back. If none of these apply, the honest answer is that the best sleep position is the one that lets you sleep deeply and wake up without pain. Most of the differences between left and right side sleeping are small for healthy adults, and consistently getting enough quality sleep matters far more than which side you choose.