Quick Answer: The best side to sleep on depends on your specific health situation. Left side is better for GERD, pregnancy after 28 weeks, and heartburn. Right side may be more comfortable for some heart failure patients. For shoulder or hip pain, sleep on the unaffected side. Most healthy adults can sleep on whichever side they find comfortable -- the mattress support matters more than the direction.
Table of Contents
Reading Time: 8 minutes
- Why the Answer Depends on Your Condition
- GERD and Acid Reflux: Left Side
- Pregnancy: Left Side After 28 Weeks
- Heart Failure: Often Right Side
- Shoulder Pain: Opposite to Affected Side
- Hip Pain and Bursitis: Opposite to Affected Side
- Heartburn in Pregnancy: Left Side for Both
- Conditions Decision Table
- The Role Your Mattress Plays
- Frequently Asked Questions
- Sources
- Visit Our Brantford Showroom
Why the Answer Depends on Your Condition
The question of left versus right side sleeping sounds simple but the answer changes meaningfully depending on what a person is dealing with. For acid reflux, left side is clearly better. For some people with heart failure, right side is more comfortable. For shoulder pain, the answer is "neither -- sleep on the other one."
This article maps the research on each major condition so you can find the recommendation that actually applies to your situation, rather than a one-size answer that may not suit you.
Dorothy at Mattress Miracle notes that this is frequently one of the more complicated sleep questions she works through with customers. "People come in having read something about left-side sleeping being 'better,' but that is not always true for their specific situation," she says. "The answer is always, for whom?"
GERD and Acid Reflux: Left Side Is Clearly Better
Gastroesophageal reflux disease (GERD) and frequent acid reflux are among the most common sleep disruptors. For people with GERD, left-side sleeping is the most evidence-supported position recommendation available.
The reason is anatomical. The stomach sits primarily on the left side of the abdomen. The junction between the stomach and oesophagus (the lower oesophageal sphincter) is positioned such that when lying on the left, stomach acid pools in the fundus away from the junction. When lying on the right, acid pools near the junction and refluxes more easily.
Multiple studies using objective oesophageal pH monitoring have confirmed that right-side sleeping produces significantly more acid exposure time in the oesophagus than left-side sleeping. The difference is meaningful: some studies show a 50% or greater reduction in oesophageal acid exposure with position change from right to left.
For GERD: sleep on the left side. Elevate the head 15 to 20 centimetres with a wedge pillow or adjustable base for compounded benefit.
Pregnancy: Left Side After 28 Weeks
Pregnant women are specifically advised to sleep on the left side from approximately 28 weeks gestation. The inferior vena cava, a large vein returning blood from the lower body to the heart, runs to the right of the spine. A growing uterus can compress it when a pregnant person lies on their back or right side, reducing blood return to the heart and circulation to the placenta.
Left-side sleeping shifts uterine weight away from the inferior vena cava, maintaining better blood flow. Multiple studies, including the 2011 Stacey BMJ study, found associations between back sleeping and increased risk of late stillbirth. Guidelines in Canada, the UK, Australia, and New Zealand now incorporate this recommendation.
For pregnancy after 28 weeks: sleep on the left side. A full-length body pillow positioned behind the back helps maintain this position.
Heart Failure: Often Right Side, With Caveats
Heart failure is one situation where right-side sleeping may be preferable, and it is also the main exception to the general preference for left-side sleeping in many contexts.
When lying on the left side, the heart sits closer to the chest wall. People with heart failure often report that this position increases the sensation of their heart beating, which can be uncomfortable or anxiety-provoking. Left-side sleeping may also alter haemodynamic loading in heart failure in ways that are less favourable for some patients.
Right-side sleeping may reduce this sensation and, in some research contexts, has been associated with reduced cardiac workload for heart failure patients. However, this is a nuanced area and guidance varies by individual case, stage of heart failure, and specific haemodynamic profile. Anyone with a diagnosed heart condition should discuss sleep position specifically with their cardiologist.
For heart failure: discuss with your cardiologist. Many patients find right-side sleeping more comfortable; some cardiologists recommend it for specific presentations.
When Left and Right Recommendations Conflict
Some people have both GERD and a heart condition. In these cases, the risks and benefits of each position should be weighed with medical guidance. For mild GERD and significant heart failure, the heart condition considerations may take priority. Head elevation (which helps GERD regardless of side) can be used alongside right-side positioning. This is a conversation for your physician, not a decision to make alone.
8 min read
Shoulder Pain: Avoid the Affected Side
Shoulder pain from rotator cuff injury, bursitis, impingement syndrome, or arthritis is significantly worsened by sleeping on the affected shoulder. The problem is sustained pressure: lying on a painful shoulder for 7-8 hours continuously compresses the joint and surrounding soft tissue, increasing inflammation and pain, and often producing the experience of waking with worse shoulder pain than existed at bedtime.
The recommendation is to sleep on the opposite shoulder. A small pillow or soft padding tucked between the arm and torso on the unaffected side can help maintain a comfortable side-lying position that keeps the painful shoulder free from pressure.
Back sleeping is also an option for shoulder pain, though many people with rotator cuff issues find that the arm position during back sleeping (arms flat by the sides, or on the stomach) can itself strain the shoulder. Experimenting with arm position is worthwhile.
For shoulder pain: sleep on the unaffected side. Avoid sleeping on the painful shoulder until inflammation and pain are resolved.
Hip Pain and Bursitis: Avoid the Affected Side
Hip bursitis (inflammation of the bursa, the small fluid-filled sac near the hip joint) is a common complaint that often worsens overnight. Trochanteric bursitis, inflammation at the outer hip, is particularly aggravated by direct pressure -- exactly what side sleeping on that hip provides.
Like shoulder pain, the management is to sleep on the other side. For hip pain generally, a pillow between the knees is valuable regardless of which side is preferred: it prevents the top hip from dropping forward and rotating the pelvis, which strains the hip joint even on the unaffected side.
A mattress that is too firm compounds hip pain by creating excessive pressure at the hip. Side sleepers with hip problems generally do better on a medium to medium-soft mattress that allows the hip to sink slightly without creating poor spinal alignment.
For hip bursitis or hip pain: sleep on the unaffected side. Use a pillow between the knees. Consider mattress softness.
The Pillow Between the Knees: Simple, Effective
Regardless of which side is preferred, a pillow between the knees is one of the simplest and most consistently effective sleep position modifications for side sleepers. It prevents the top leg from pulling the hip and lower spine into a rotated, strained position. People with lower back pain, hip pain, or sciatica often notice a difference within a few nights. Any pillow works, but a body pillow or a specifically shaped knee pillow maintains position more reliably than a standard pillow.
Heartburn in Pregnancy: Left Side Addresses Both
Heartburn is extremely common in the second and third trimesters of pregnancy, caused by the growing uterus pushing up against the stomach and by hormonal changes that relax the lower oesophageal sphincter. Many pregnant women deal with both pregnancy positioning concerns and nighttime heartburn simultaneously.
Left-side sleeping addresses both. It improves inferior vena cava circulation (the pregnancy positioning concern) and positions the stomach more favourably for preventing acid reflux (the heartburn concern). This is a situation where both evidence-based recommendations point in the same direction, making the decision straightforward.
A wedge pillow or elevated head adds further heartburn relief without conflicting with the left-side positioning recommendation.
Conditions Decision Table
| Your Condition | Best Side | Key Reason |
|---|---|---|
| Acid reflux / GERD | Left | Keeps stomach acid away from oesophageal sphincter |
| Pregnancy (after 28 weeks) | Left | Reduces inferior vena cava compression |
| Heart failure (discuss with cardiologist) | Right (often) | Reduces sensation of heart against chest wall |
| Shoulder pain (right shoulder) | Left | Avoids compressing inflamed right shoulder |
| Shoulder pain (left shoulder) | Right | Avoids compressing inflamed left shoulder |
| Hip bursitis / hip pain (right hip) | Left | Avoids pressure on inflamed right hip bursa |
| Hip bursitis / hip pain (left hip) | Right | Avoids pressure on inflamed left hip bursa |
| Heartburn in pregnancy | Left | Addresses both GERD mechanics and vascular circulation |
| Snoring / sleep apnea | Either side (avoid back) | Side sleeping keeps airway from collapsing |
| Healthy adult, no specific condition | Whichever is comfortable | No strong evidence for one side over the other |
The Role Your Mattress Plays
Whatever side is recommended for your condition, its benefits depend on a mattress that supports that position properly.
For left-side sleeping (GERD, pregnancy), a mattress needs adequate pressure relief at the left shoulder and hip to prevent those points from becoming painful during extended left-side sleep. Too firm a surface makes left-side sleeping uncomfortable enough that people naturally roll off it -- defeating the purpose of the recommendation.
For right-side sleeping (heart failure management), the same logic applies to the right shoulder and hip. A mattress topper can add targeted pressure relief without replacing an entire mattress.
For people avoiding a painful shoulder or hip, the mattress needs to provide enough support that the good side does not also become uncomfortable from bearing all the weight.
Brad at Mattress Miracle, who has helped Brantford customers navigate sleep and health questions since 1997, recommends bringing specific health context to the mattress conversation. "If someone has a GERD recommendation to sleep on the left side but their current mattress is too firm for side sleeping to be comfortable, they end up ignoring the medical advice," he says. "The mattress has to enable the recommended position, not fight against it."
Finding the Right Side-Sleeping Mattress at Mattress Miracle
Our team will ask about your sleep position, any health conditions that affect it, and body type before recommending a mattress. The goal is a surface that makes it easy and comfortable to sleep in the position that is best for your health. Come in and talk through your specific situation -- there is no commission pressure, just honest guidance.
Shop: Adjustable Beds at Mattress Miracle
Shop This Topic at Mattress Miracle
Popular picks at Mattress Miracle:
Or explore the full mattress range in our Brantford showroom.
Find Your Perfect Mattress at Mattress Miracle
We are a family-owned mattress store in Brantford, helping our community sleep better since 1997. Come try mattresses in person and get honest, no-pressure advice.
441 1/2 West Street, Brantford, Ontario
Call 519-770-0001Frequently Asked Questions
I have GERD but sleep better on my right side. What should I do?
Left-side sleeping takes time to adjust to if you are a habitual right-side sleeper. Try transitioning gradually with a body pillow behind your back to maintain the left-side position. Some people find the discomfort of the adjustment period resolves within a week or two once the body adapts. In the meantime, head elevation (wedge pillow or adjustable base) helps reduce reflux regardless of which side you are on.
Can my mattress make shoulder pain worse even when I am sleeping on the good side?
Yes. If the mattress is too firm, the shoulder of the "good" side bears all the body's weight without adequate cushioning, and can become sore itself. A medium mattress or a mattress topper with pressure-relieving properties helps distribute the load more evenly.
I have both hip bursitis and GERD. Which recommendation wins?
These recommendations are typically compatible. If bursitis is on the right hip, sleeping on the left side avoids the painful right hip and also addresses GERD. If bursitis is on the left hip, you face a conflict -- discuss with your doctor. In most cases, a wedge pillow for GERD combined with right-side sleeping for the hip may be the compromise, as head elevation reduces GERD somewhat regardless of which side you are on.
Does it matter which side I start on if I roll during the night?
For GERD and pregnancy, the evidence focuses on the position you go to sleep in, since that is the period of most sustained, intentional positioning. Natural rolling during sleep is normal and expected. The goal is to start in the recommended position and use positioning aids (body pillow, wedge) to extend time in that position as much as comfortably possible.
Sources
- Katz LC, Just R, Castell DO. "Body position affects recumbent postprandial reflux." Journal of Clinical Gastroenterology. 1994;18(4):280-3.
- Stacey T, Thompson JMD, et al. "Association between maternal sleep practices and risk of late stillbirth." BMJ. 2011;342:d3403.
- Reddy R, Guntupalli K, et al. "Sleep in heart failure." Sleep Medicine Reviews. 2009;13(4):243-255.
- Bunker CB, Dowd PM. "Shoulder pain and sleep position." British Journal of Rheumatology. 1994.
- Oksenberg A, Silverberg DS. "The effect of body posture on sleep-related breathing disorders." Sleep Medicine Reviews. 1998;2(3):139-162.
Visit Our Brantford Showroom
We are located at 441½ West Street in downtown Brantford. Free parking available. Our team does not work on commission, so you get honest advice based on your needs.
Mattress Miracle -- 441½ West Street, Brantford, ON -- (519) 770-0001
Hours: Monday--Wednesday 10am--6pm, Thursday--Friday 10am--7pm, Saturday 10am--5pm, Sunday 12pm--4pm.
If a health condition is affecting which side you can comfortably sleep on, come in and let us help you find a mattress that makes the recommended position achievable and comfortable. Dorothy and Talia are both on hand to help.