Sleeping on your side is the best position for most people, and the left side offers the most overall benefits. That said, the “best” side depends on your specific health concerns. Left-side sleeping is better for digestion and acid reflux, while right-side sleeping may be slightly better for brain waste clearance and heart comfort. Here’s how to choose based on what matters most to you.
Why Side Sleeping Beats Back or Stomach
Before choosing a side, it helps to know that sleeping on either side is generally better than sleeping on your back or stomach. Dr. Virend Somers, a cardiologist and director of the sleep facility within Mayo Clinic’s Center for Clinical and Translational Science, notes there is a “host of evidence” suggesting side sleeping is the healthiest overall position.
The biggest advantage is breathing. Lying on your back lets gravity pull your tongue and soft palate backward, which narrows your airway and worsens snoring and sleep apnea. Switching to a lateral (side) position cuts the number of breathing disruptions roughly in half. In one study, people with central sleep apnea experienced about 43 breathing events per hour on their backs during stage 2 sleep, compared to just 14 per hour on their side. That pattern held across every sleep stage measured.
Sleeping on your back also appears to be worse for long-term brain health. Your brain has a waste-clearance system that operates mostly during sleep, flushing out metabolic byproducts through cerebrospinal fluid. Research has found that people with dementia spend a much larger percentage of their sleep time on their backs compared to healthy controls, suggesting a link between the supine position and reduced brain clearance over time.
Left Side: Best for Digestion and Reflux
If you deal with heartburn, acid reflux, or GERD, sleeping on your left side is the clear winner. The reason is simple anatomy: your stomach curves to the left. When you lie on your left side, your esophagus sits above your stomach, so gravity keeps acid where it belongs. Flip to the right, and that relationship reverses. Your stomach ends up higher than your esophagus, making it far easier for acid to flow upward.
A systematic review and meta-analysis published in the World Journal of Clinical Cases confirmed that right-side sleeping triggers more heartburn and reflux episodes than any other position. If your lower esophageal sphincter (the valve between your esophagus and stomach) is weakened or tends to relax during sleep, the right-side position essentially opens the door for stomach contents to travel the wrong direction. Left-side sleeping closes it.
Right Side: Slightly Better for Brain Clearance
Your brain’s waste-clearance system, sometimes called the glymphatic system, works by moving cerebrospinal fluid through brain tissue to flush out proteins and metabolic debris. Gravity and blood flow patterns change depending on your body position, and research published in Brain Sciences found that this system works most efficiently in the right lateral sleeping position. More fluid clearance occurred on the right side compared to both back and stomach sleeping.
This doesn’t mean you need to sleep exclusively on your right side for brain health. Side sleeping in general is significantly better than back sleeping for waste clearance. But if brain health is a priority and you don’t have reflux issues pulling you to the left, the right side has a slight edge.
Heart Health: Both Sides Are Safe
You may have heard that sleeping on your left side puts pressure on your heart. There’s a grain of truth here: imaging studies show that left-side sleeping causes the heart to shift position slightly within the chest, and some people with heart failure report more discomfort on the left. However, there is no evidence that sleeping on either side increases your risk of developing heart problems.
Sleeping on your right side keeps the heart in a more stable position, with almost no measurable change in electrical activity on ECG readings. For most healthy adults, this difference is negligible. If you have heart failure and notice discomfort on your left side, the right side may feel better, but this is about comfort, not safety.
Pregnancy: Left or Right, Just Not on Your Back
Pregnant women have long been told to sleep on their left side, and that advice isn’t wrong, but it’s more nuanced than many people realize. An individual patient data meta-analysis reviewed by the UK’s National Institute for Health and Care Excellence found that going to sleep on your back after 28 weeks approximately doubled the odds of stillbirth and tripled the odds of the baby being born small for gestational age, compared to sleeping on the left side.
The important finding, though, is that sleeping on the right side carried no increased risk compared to the left. The evidence does not support the idea that right-side sleeping is dangerous during pregnancy. The key takeaway: after 28 weeks, try to fall asleep on either side rather than flat on your back. If you wake up on your back, simply roll over. The going-to-sleep position is what matters most, since that’s where you spend the longest stretch.
Shoulder and Hip Pain to Watch For
The downside of side sleeping is pressure on your lower shoulder and hip. If you already have shoulder bursitis or impingement, sleeping on the affected side will almost certainly make the pain worse. The fix is straightforward: sleep on the opposite side, or place a pillow between your knees to keep your hips aligned and reduce strain on the lower hip joint.
People who alternate sides throughout the night tend to distribute the pressure more evenly. If you find yourself waking with a numb arm or aching shoulder, switching sides or adjusting your pillow setup is usually enough to solve it.
Pillow Height for Side Sleepers
Side sleepers need a taller pillow than back sleepers because the gap between your head and the mattress is wider. A pillow that’s too thin lets your head tilt downward, compressing your neck. One that’s too thick pushes your head upward, creating strain on the opposite side.
Most side sleepers do best with a pillow between five and seven inches in height, classified as mid to high loft. A quick test: when your head is on the pillow, your ear should line up level with your shoulder. If you can see or feel your head tilting in either direction, the pillow height is off. You may also want a firm or medium-density pillow, since a soft one will compress under your head’s weight and lose the height you need.
Facial Wrinkles From Side Sleeping
One lesser-known trade-off of side sleeping is its effect on your skin. When half your face is pressed into a pillow for hours, the sustained compression creates what dermatologists call sleep wrinkles. These are distinct from expression lines and show up as crow’s feet, lines around the mouth, flattening of the forehead, and deepened nasolabial folds on the side you sleep on.
If this concerns you, silk or satin pillowcases reduce friction, and specially contoured pillows can redistribute pressure away from wrinkle-prone areas. Alternating sides throughout the night also helps prevent asymmetric aging. For most people, the cardiovascular and digestive benefits of side sleeping far outweigh the cosmetic effects, but it’s worth knowing about if you’ve noticed one-sided facial changes.
Choosing Your Best Side
For the average healthy adult, left-side sleeping is the safest default. It helps with acid reflux, keeps your airway open, and supports digestion. If you don’t have reflux issues and want to optimize brain waste clearance, the right side has a slight advantage. During pregnancy after 28 weeks, either side is fine as long as you avoid falling asleep on your back. And if you have shoulder or hip pain, sleep on whichever side doesn’t aggravate it.
Most people shift positions multiple times per night without realizing it, and that’s perfectly normal. The position you fall asleep in is the one you spend the most time in, so start on the side that addresses your biggest health priority and let your body adjust from there.