Which Side Should I Sleep On? The Science Behind Sleep Position And Your Biology

Most of us fall asleep in the same position every night without thinking about what it means for our body. But your sleep position influences far more than comfort. It can shape digestion, reflux, venous return, musculoskeletal alignment, even how your brain clears metabolic waste during deep sleep.

This isn't about perfecting posture or creating rules around rest. It's about understanding the quiet biological processes happening overnight, and how simple positioning may support them.

So which side should you sleep on? Here's what the current research suggests.

What Each Sleep Position May Influence

Different postures influence different physiological systems.

Left Side Sleeping is often associated with:

• Digestive comfort
• Reflux support
• Venous drainage
• Emerging glymphatic clearance theories

Right Side Sleeping is commonly linked with:

• Comfort and spine alignment
• Alternating pressure points
• Individual breathing patterns

Back Sleeping can support:

• Neutral spinal alignment
• Reduced facial compression

Stomach Sleeping may:

• Increase cervical strain
• Affect spinal extension
• Increase facial pressure

No single position is perfect. But certain habitual postures appear to work with the body's natural processes more elegantly, especially during deep sleep when the nervous system shifts into repair mode.

Best Sleep Position For Glymphatic Drainage And Brain Health Overnight

During deep sleep, the brain activates its glymphatic system, a specialised clearance pathway that moves metabolic by-products such as beta-amyloid out of neural tissue. Early imaging suggests side sleeping supports glymphatic activity more effectively than lying flat, likely due to how cerebrospinal fluid circulates.[1]

The relationship between side sleeping and cerebral venous drainage remains an area of active investigation. While lateral sleeping generally appears to support glymphatic function better than supine positioning - lying flat on your back, face up - whether left or right side is optimal remains unclear, with preliminary anatomical theories suggesting either side may offer advantages depending on individual the individual's venous anatomy.[2]

Best Sleep Position For Digestive Comfort And Reflux Relief

Your stomach lies mostly on the left. When you sleep on this side, gravity naturally positions gastric contents lower, helping reduce upward movement into the oesophagus. Several studies suggest left side sleeping may reduce night-time reflux more effectively than lying on the right or flat.[3]

Left may support:

• Reflux comfort
• Gastric settling
• Digestive ease

On the other hand, the right may:

• Allow reflux to rise more easily in sensitive individuals

This isn't treatment, just a simple anatomical observation that many people find comforting in real life.

Best Sleep Position For Circulation And Venous Return

The inferior vena cava (IVC) sits slightly to the right of the spine. When we lie on the right, body weight may apply gentle pressure to this blood vessel.[4] Studies examining lateral body positions have confirmed that the IVC is larger in the left lateral position compared to the right, suggesting reduced compression.[5] Lying on the left may therefore support venous return.

This is one reason why left side sleeping is often recommended in pregnancy, where circulation demands are naturally higher.[6]

Best Sleep Position For Back Pain And Spinal Alignment

For musculoskeletal comfort, side sleeping frequently supports the lower back, especially with a pillow between the knees to keep hips and spine aligned.[7]

Supportive strategies:

• Left side + knee pillow
• Right side + knee pillow
• Supportive back sleeping for some individuals

Less favourable:

• Stomach sleeping (requires cervical rotation and increases lumbar extension)

If back comfort is your priority, side sleeping, either side, usually offers the most structural support.

Best Sleep Position For Skin, Hair And Overnight Pressure

Mechanical pressure matters. Repeated compression on one side of the face can contribute to sleep wrinkles over time.[8] Hair can also be affected by friction and tension from pillow contact.

Supportive approaches:

• Alternating sides
• Low-friction pillowcases
• Pillows that reduce facial pressure

Here, the specific side matters less than avoiding repetitive mechanical imprinting night after night.

So Which Side Is "Best"?

When we look at anatomical reasoning, the left side supports the largest number of biological processes simultaneously, from digestive comfort to venous return.

Left Side May Support

• Reflux comfort
• Digestion
• Venous return
• Emerging glymphatic theories

Right Side May Support

• Comfort preference
• Alternating facial pressure
• Specific breathing patterns

The best sleep position is the one that helps you stay asleep deeply and comfortably. Without uninterrupted deep sleep, glymphatic drainage cannot occur, and deep sleep depends more on circadian timing than posture.

What Matters More Than Position

The most powerful drivers of overnight repair are:

• Deep sleep
• Strong circadian rhythm[9]
• Regulated melatonin levels[10]
• Relaxed nervous system[11]
• Consistent bedtime[12]
• Reduced overnight light exposure[13]

Position is an elegant amplifier, not the foundation.

The Bottom Line

If digestion, reflux or nighttime clearance interest you, the left side is a worthwhile experiment. But your body's natural intelligence is extraordinary; comfort and continuity may be equally valuable.

BON CHARGE: This content is for general education and is not medical advice. Our products are not intended to diagnose, treat, cure, or prevent any disease. Always follow product instructions and consult a qualified healthcare professional for guidance tailored to you. Individual results may vary.

References

1. Lee, H. et al. The effect of body posture on brain glymphatic transport. J. Neurosci. 35, 11034–11044 (2015).
2. Simka, M., Czaja, J. & Kowalczyk, D. Collapsibility of the internal jugular veins in the lateral decubitus body position: a potential protective role of the cerebral venous outflow against neurodegeneration. Med. Hypotheses 133, 109397 (2019).
3. Simadibrata, D. M. et al. Left lateral decubitus sleeping position is associated with improved gastroesophageal reflux disease symptoms: a systematic review and meta-analysis. World J. Clin. Cases 11, 7329–7336 (2023).
4. Nakao, S. et al. Effects of positional changes on inferior vena caval size and dynamics and correlations with right-sided cardiac pressure. Am. J. Cardiol. 59, 125–132 (1987).
5. Mookadam, F. et al. Effect of positional changes on inferior vena cava size. Eur. J. Echocardiogr. 12, 322–325 (2011).
6. O'Brien, L. M. et al. Maternal sleep practices and stillbirth: findings from an international case-control study. Birth 46, 344–354 (2019).
7. Cary, D. et al. Examining relationships between sleep posture, waking spinal symptoms and quality of sleep. PLoS One 16, e0260582 (2021).
8. Anson, G. et al. Sleep wrinkles: facial aging and facial distortion during sleep. Aesthet. Surg. J. 36, 931–940 (2016).
9. Cajochen, C. et al. Role of melatonin in the regulation of human circadian rhythms and sleep. J. Neuroendocrinol. 15, 432–437 (2003).
10. Zisapel, N. New perspectives on the role of melatonin in human sleep, circadian rhythms and their regulation. Br. J. Pharmacol. 175, 3190–3199 (2018).
11. de Zambotti, M. et al. Dynamic coupling between the central and autonomic nervous systems during sleep. Neurosci. Biobehav. Rev. 90, 84–103 (2018).
12. Cribb, L. et al. Sleep regularity and mortality: a prospective analysis in the UK Biobank. eLife 12, e88359 (2023).
13. Gooley, J. J. et al. Exposure to room light before bedtime suppresses melatonin onset and shortens melatonin duration in humans. J. Clin. Endocrinol. Metab. 96, E463–E472 (2011).