Sleeping on Your Left Side: Heartburn, Pregnancy and the Evidence

This Is Why You Should Be Sleeping On Your Left Side

Is sleeping on your left side really better? For one common problem, the answer is a cautious yes: lying on your left side seems to reduce night-time heartburn and acid reflux, and a 2022 study measured exactly that. For pregnancy, the advice that matters is to fall asleep on your side rather than your back, and either side is fine. Claims that the left side helps your body "flush toxins" through the lymphatic system have no good evidence behind them.

Here is what is known about each claim, why the stomach's shape matters, and some simple ways to change a sleeping habit you have had for years.

Why the left side can ease heartburn

The diagram above shows the basic idea. Your stomach sits mostly on the left of your abdomen, and the oesophagus (food pipe) joins it from the right-hand side of the stomach. When you lie on your left, the stomach and its acidic contents sit below that junction, so gravity helps keep acid where it belongs. Lie on your right and the junction can end up lower than the pool of stomach juice, which makes it easier for acid to creep upward.

That is the theory, and it now has measurement behind it. In a study published in the American Journal of Gastroenterology in February 2022, researchers in Amsterdam led by Jeroen Schuitenmaker tracked 57 people with reflux overnight, using a probe in the oesophagus and a device recording their sleeping position. Acid exposure was lowest on the left side and highest on the right, and acid was cleared fastest on the left: a median of 35 seconds, compared with 76 seconds on the back and 90 seconds on the right.

It is a small study, and one author disclosed links to a company making sleep-position devices, but it fits with earlier research and with what many people with heartburn notice for themselves. Pregnant women often feel it most strongly, because the growing womb pushes up on the stomach.

(The video originally embedded here is no longer available on YouTube.)

Other ways to calm night-time reflux

Sleeping position is only one part of the picture. The NHS lists several self-help measures for heartburn and acid reflux, including:

Eating smaller meals more often, and not eating in the 3 to 4 hours before bed.
Raising the head of your bed by about 10 to 20cm, with blocks under the bed legs or a wedge under the mattress, so your chest and head are above your waist. Extra pillows are not recommended, because bending at the middle can increase pressure on the stomach.
Avoiding foods and drinks that trigger your symptoms, which for many people include coffee, alcohol, chocolate, tomatoes and fatty or spicy food.
Avoiding tight clothing around the waist, stopping smoking and finding ways to relax.

The NHS recommends seeing a GP if heartburn happens most days, if pharmacy remedies and lifestyle changes are not helping, or if you also have symptoms such as food getting stuck, frequent vomiting or unexplained weight loss. Any chest pain that might be your heart needs urgent medical help, not a change of sleeping position.

Pregnancy: your side matters more than which side

For years, pregnant women were told to sleep on their left side specifically. Current NHS guidance is simpler. Going to sleep on your back after 28 weeks of pregnancy is linked to a higher risk of stillbirth, possibly because of reduced blood and oxygen flow to the baby, so the safest way to fall asleep is on your side, left or right.

If you wake up on your back, there is no need to panic; just turn onto your side before you drift off again. Many women still prefer the left in later pregnancy because it helps with heartburn, but that is about comfort, not safety. Your midwife or doctor is the right person to ask about anything specific to your pregnancy.

The lymphatic "toxin" claim

Many articles say the left is the "dominant lymphatic side", so sleeping on it helps the body remove toxins and waste. There is a grain of anatomy behind this. The lymphatic system carries fluid called lymph back into the blood, and its largest vessel, the thoracic duct, collects lymph from most of the body and empties it into the veins at the base of the neck on the left. A smaller duct handles the right side of the chest, the right arm and the right side of the head.

What does not follow is the health claim. The thoracic duct carries up to about 4 litres of lymph a day in adults, and it keeps doing so whichever way you lie. No study has shown that sleeping on your left speeds up "detox" or improves health through the lymphatic system, so it is best not to choose a position for that reason. Your liver and kidneys, not your pillow, do the work of clearing waste.

Side sleeping and snoring

There is another solid reason to sleep on your side, whichever one you pick. The NHS lists sleeping on your back as something that makes snoring more likely, and recommends side sleeping as one of the first things to try. When you lie on your back, the tongue and soft tissues of the throat can fall back and narrow the airway.

Loud snoring with gasping, choking or pauses in breathing can be a sign of sleep apnoea, which needs a doctor's assessment. If a partner notices this, it is worth booking an appointment.

How to train yourself to sleep on your side

Sleeping positions are stubborn habits, and you will move around during the night whatever you decide. A few tricks can help nudge you toward your side:

Use a body pillow. Place a long pillow along your back. It gives you support and makes rolling back into your old position less tempting.
Try the tennis ball trick. The NHS suggests stitching or taping a tennis ball to the back of your sleepwear, or using a special pillow or wedge, so lying on your back becomes uncomfortable.
Hug a pillow in front. A pillow between your arms and another between your knees can make side sleeping more comfortable for your shoulders and hips.
Be patient. Expect a couple of weeks before a new position feels natural.

Your mattress matters too, but you do not need an expensive one to change position. Comfort and support that suit your body are what count.

The bottom line

If you get heartburn at night, sleeping on your left side is a free, low-risk thing to try, and the evidence suggests it may help. If you are more than 28 weeks pregnant, fall asleep on either side rather than your back. If you snore, any side is better than your back. Beyond that, the best sleeping position is the one that lets you sleep well. If tiredness, reflux or snoring persist, talk to a doctor.

Want to go further? Read a chiropractor's reasons for preferring the left side with the evidence above in mind.

Sources: HealthDay, February 2022, on the American Journal of Gastroenterology study; NHS: Heartburn and acid reflux; NHS: Reducing the risk of stillbirth; NHS: Snoring; Wikipedia: Thoracic duct. The topic was also covered by Healthylifetricks and The Open Mind; featured image.

Related: