What Side Should You Sleep On?

Most people have a preferred side for sleeping, but few think about whether that preference matters for their health. The evidence suggests that for most people, either side is fine, but left-side sleeping offers some specific benefits for digestion and heartburn relief. Right-side sleeping may be better for people with certain heart conditions. Back and stomach sleeping come with their own trade-offs that are worth understanding before you settle in tonight.

What Side Should You Sleep On?

The short answer is that left-side sleeping is the best choice for most people. Research has consistently shown that sleeping on your left side helps reduce acid reflux symptoms and improves digestion. This is because your stomach sits on the left side of your body, and when you lie on your left, gravity helps keep stomach acid where it belongs.

Left-side sleeping also takes pressure off your liver, which is the largest organ on your right side. Pregnant women are specifically advised to sleep on their left side to improve blood flow to the fetus. For people with heart failure, right-side sleeping is often recommended instead, because it may reduce pressure on the heart.

Does Sleeping on Your Left Side Really Help Digestion?

Yes, and the anatomy explains why. Your stomach is located on the left side of your abdomen, and the valve that connects your stomach to your esophagus sits slightly to the right. When you sleep on your left side, that valve stays above the level of stomach acid. When you sleep on your right side, the valve can be submerged in acid, which makes reflux more likely.

A study published in the Journal of Clinical Gastroenterology found that patients with acid reflux had significantly more nighttime reflux episodes when sleeping on their right side compared to their left. The difference was large enough that researchers recommended left-side sleeping as a simple, free addition to reflux treatment plans.

For people with frequent heartburn or GERD, this is one of the easiest lifestyle changes to make. It costs nothing, requires no equipment, and can reduce symptoms within the first night for some people.

Is Left-Side Sleeping Better for Your Heart?

This is where the evidence gets more specific. For healthy people, sleeping on either side does not meaningfully affect heart function. Your heart is well protected inside your chest, and its position shifts only slightly when you change sides.

For people with congestive heart failure, the story is different. Some studies have found that sleeping on the left side can cause uncomfortable sensations and changes in heart rhythm for these patients. The heart is positioned slightly to the left of center in the chest, and lying on that side may shift it against the chest wall in ways that some people find uncomfortable.

Research published in the Journal of the American College of Cardiology found that patients with heart failure often preferred sleeping on their right side. The study suggested this was because left-side sleeping increased chest discomfort and awareness of their heartbeat. If you have heart failure, talk to your cardiologist about which side is right for you.

What About Sleeping on Your Back?

Back sleeping is the best position for spine alignment. Your head, neck, and spine can rest in a neutral position, which reduces pressure on your joints and muscles. Many physical therapists recommend back sleeping for people with back or neck pain.

But back sleeping has a significant downside. It makes sleep apnea worse. When you lie on your back, gravity pulls your tongue and soft palate backward, which can narrow or block your airway. For people who snore or have obstructive sleep apnea, back sleeping is the worst position.

Some people also experience lower back pain when sleeping on their back because the natural curve of the lower spine is not always fully supported. Placing a pillow under your knees can help by maintaining the natural curve of your spine.

Is Stomach Sleeping Ever a Good Idea?

Stomach sleeping is the least recommended position by most experts. It forces your neck to stay rotated to one side for hours, which can strain the muscles and joints in your neck and upper back. Over time, this can lead to chronic neck pain and headaches.

The only real advantage of stomach sleeping is that it keeps your airway more open than back sleeping. People who snore often find they snore less on their stomachs. But the neck strain usually outweighs this benefit.

If you are a dedicated stomach sleeper and cannot switch positions, using a very thin pillow or no pillow at all can reduce the angle your neck has to turn. Placing a flat pillow under your pelvis can also help keep your spine in better alignment.

What Is the Best Sleeping Position for Pregnancy?

Left-side sleeping is the clear recommendation during pregnancy. The inferior vena cava, which is a large vein that returns blood from your lower body to your heart, runs along the right side of your spine. Lying on your left side keeps your growing uterus from pressing on this vein.

This pressure on the vena cava can reduce blood flow to your heart and to your baby. Clinical guidelines from the American College of Obstetricians and Gynecologists recommend left-side sleeping during the third trimester. Some research suggests that sleeping on your back in late pregnancy may also be associated with a higher risk of stillbirth, though the overall risk remains low.

If you find yourself waking up on your back during pregnancy, do not panic. Simply roll back to your left side and go back to sleep. Using a full-body pregnancy pillow can help you stay in position through the night.

How to Train Yourself to Sleep on a Different Side

Most people do not consciously choose their sleeping position. You likely fall asleep in one position and wake up in another. Changing your habitual side takes patience, but it is possible.

Start by placing pillows behind your back when you fall asleep on your desired side. This prevents you from rolling onto your back or your other side during the night. Some people find that sewing a tennis ball into the front of a pajama shirt discourages stomach sleeping, though this is a more aggressive approach.

Give yourself at least two weeks to adjust. Most sleep researchers agree that position changes take about 14 to 21 days to become automatic. You may sleep worse for the first few nights, but your body will adapt.

Remember that your sleeping position matters far less than getting enough quality sleep. If you sleep well on your right side and have no reflux, heart issues, or pregnancy, there is no strong reason to force a change.

Does Your Pillow and Mattress Change the Answer?

Your pillow matters more than you might think. Side sleepers need a thicker pillow to fill the space between their ear and the outside of their shoulder. A pillow that is too thin lets your neck bend sideways toward the mattress, which can cause morning stiffness.

Back sleepers need a thinner pillow that supports the natural curve of the neck without pushing the head too far forward. Stomach sleepers should use the thinnest pillow possible or none at all.

Mattress firmness also plays a role. Side sleepers generally need a medium to medium-soft mattress that allows the hips and shoulders to sink slightly. This keeps the spine aligned. A mattress that is too firm creates pressure points at the shoulder and hip for side sleepers.

No mattress or pillow can fully compensate for a position that causes you pain or disrupts your breathing. Choose your position first based on your health needs, then choose your bedding to support that position.