Is it better to sleep on your left side? For heartburn and acid reflux, there is reasonable evidence that it is: studies find less acid in the gullet and faster clearance when people with reflux lie on their left. For pregnancy, experts also favour the left side in the later months. For most other people, though, left or right makes little measurable difference, and two of the popular claims, about the heart and the lymphatic system, are not backed by good evidence. Some people with heart failure actually find the left side uncomfortable.
The four reasons below were popularised by Dr John Douillard, an American chiropractor and Ayurvedic practitioner who runs the LifeSpa website, and spread widely through viral health pages. Here is what each one claims and how well it holds up.
Why sleep position matters at all
Most adults need seven or more hours of sleep, and quality counts as much as quantity. Poor sleep is linked with higher blood pressure, weight gain, low mood and stress. Position can influence comfort, breathing, reflux and joint pain, so it is a fair thing to think about, as long as we stay clear about which effects are proven.
Douillard frames the left side as old wisdom with modern benefits. In his words, emphasising the left side for rest offers “time-tested wisdom for very real health and longevity benefits.” Longevity is a big promise, and no study has tested whether sleeping side affects lifespan. The specific claims are easier to check.
1. Heartburn and reflux: the best-supported claim
The stomach sits mostly to the left of the body’s midline, and the junction with the gullet sits above it when you lie on your left. Gravity then helps keep acid where it belongs. Lying on the right side places the stomach above the junction, which makes reflux easier.
A 2023 systematic review and meta-analysis in the World Journal of Clinical Cases pooled three studies of people with gastro-oesophageal reflux disease (GERD). Compared with the right side, left-side sleeping cut the share of time the gullet was exposed to acid by about two percentage points and shortened acid clearance by roughly 80 seconds per episode. Lying on the back was no better than the right side. In a two-week randomised trial of 100 patients, a wearable device that nudged sleepers onto their left side led to more reflux-free nights and better night-time symptom scores than a sham device.
The authors were careful: only three studies and about 170 patients were included, most participants were overweight women, and staying on one side all night is hard. Still, for people with night-time heartburn, trying the left side is low-risk and reasonable. Raising the head of the bed, avoiding late meals and losing excess weight are other well-established measures.
2. Heart health: not supported, and sometimes the opposite
The claim is that lying on the side where the heart sits makes it pump more efficiently. There is no good evidence for this in healthy people, whose hearts cope well with any position.
For people with heart failure the picture can even reverse. The Sleep Foundation notes that some people with heart failure become short of breath lying on their left side but not their right, and that right-side sleeping may be preferred by people with heart conditions. Lying on the left also brings the heart closer to the chest wall, which can make the heartbeat more noticeable. If you have a heart condition and find a position uncomfortable, mention it to your doctor rather than forcing a particular side.
3. The lymphatic system: a real fact stretched too far
There is a grain of anatomy here. The thoracic duct, the body’s largest lymph vessel, collects lymph from most of the body and empties into the veins at the base of the neck on the left side. Only the right arm, right chest, and the right side of the head and neck drain through a smaller right lymphatic duct.
That does not make the left side of the body the “lymphatic side”, and there is no evidence that lying on it speeds the removal of “toxins”. Lymph moves mainly with breathing and muscle activity, helped by valves that stop backflow, and the duct carries up to about four litres a day whichever way you lie.
A related idea concerns the brain’s glymphatic system, which clears waste during sleep. Animal studies suggest side lying may help it more than lying on the back or front, but they do not single out the left side, and human studies are still needed.
4. Snoring and sleep apnoea: either side helps
Snoring and obstructive sleep apnoea are often worse on the back, because the tongue and soft tissues fall backward and narrow the airway. Many people snore less, and some have fewer apnoea events, when they sleep on their side. This is called positional therapy, and doctors sometimes recommend it for people whose apnoea happens mainly on their back.
The research supports side sleeping in general, not the left side in particular. Sleep apnoea is also more than a snoring nuisance: it is linked to high blood pressure and heart disease, so loud snoring with pauses in breathing, gasping or heavy daytime sleepiness deserves a sleep assessment. Changing position is not a substitute for treatment such as CPAP when that is needed.
Pregnancy, back pain and other special cases
In the second half of pregnancy, lying flat on the back can press on major blood vessels. Experts advise side sleeping, and many recommend the left side because it may improve blood flow to the placenta and kidneys, though occasional right-side sleep is fine. Pregnant readers should follow their midwife or doctor’s advice.
For back or hip pain, a pillow between the knees keeps the pelvis level on either side. For shoulder pain, sleeping on the opposite side is usually more comfortable.
Watch Dr Douillard explain his reasoning, with a focus on digestion, in the video below.
How to try left-side sleeping
- Start the night on your left with a supportive pillow that keeps your neck level.
- Put a pillow behind your back or hug a body pillow so you are less likely to roll over.
- For reflux, combine it with a raised bedhead and a two- to three-hour gap between dinner and bed.
- Don’t worry if you wake on your other side. Comfort and enough sleep matter more than perfect positioning.
If reflux, snoring or poor sleep persists, talk to a doctor: these can be signs of conditions that have effective treatments.
Sources: Simadibrata et al., World Journal of Clinical Cases (2023); Sleep Foundation: Side Sleeping; Thoracic duct (Wikipedia); originally reported by Ideapod.
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