Sleeping on the left side

Dear Alice,

Hi there.

Is sleeping on our left side in any way harmful for the heart (or anything else)? Some people tell me we shouldn't do it and others tell me it's actually better than sleeping on our right side. What's the truth?


Dear Reader,

Getting up on the “wrong side” of the bed may lead to a grumpy day, but sleeping on the “wrong side” of your body would probably have no negative consequences for a healthy adult. “The truth,” to answer your question, is that the safest position to sleep in really depends on your health status and needs. As What position is best… for sleeping in the Go Ask Alice! archives explains, there’s not much reason to worry about your sleeping position as long as you’re comfortable, are able to get a good night’s rest, and aren’t waking up in pain. That said, there is some research out there that suggests that sleeping on the left side — or sleeping on your side in general — may not be ideal for some particular groups of people. Specifically, if you’ve got a history of heart disease or sleep apnea, have glaucoma, or have risk factors for carpal tunnel syndrome, it might be worth thinking about alternatives to sleeping on your side. Why, you ask?:

  • Heart disease: Studies have shown that people who’ve had heart troubles in the past (the physical kind, that is, not the emotional kind!) often report more chest pain and difficulty breathing when sleeping on their left. Naturally, many of them end up favoring their right side. This has led researchers to believe that patients’ bodies may be, on some level, trying to protect their weakened cardiovascular system by switching to right-side sleeping. As such, some health care providers to recommend that heart disease patients who are experiencing chest discomfort at night give right-side sleeping a go. Stay tuned as scientists investigate exactly why right-side sleeping seems to be better.
  • Sleep apnea: The key characteristics of this condition are when the muscles of the mouth and throat “collapse” during sleep and block off someone’s ability to breathe regularly. Sleep apnea is actually at its worst when a person sleeps on their back. While left-side sleeping is better than back-sleeping, studies have shown that right-side sleeping actually leads to the lowest number of symptomatic episodes overall — which means getting the max number of those precious Zzzs.
  • Glaucoma: This condition occurs when the pressure in a person’s eyeball builds up, which can lead to blindness. When a person sleeps on their side, the pressure eye that’s closest to the pillow increases a bit. While this isn’t a big deal for people with healthy eyes, the increased pressure can actually worsen cases of glaucoma, which can then mean further vision loss. So, people with glaucoma in the left eye might want to avoid sleeping on the left, and vice versa.
  • Carpal tunnel syndrome: While researchers are still working to figure out all of the risk factors for carpal tunnel syndrome (a nerve condition with pain and numbness in the wrist), one possibility that has been looked into is side-sleeping. This is because the nerves of the arm and wrist are often crushed into unnatural positions when someone falls into a deep slumber on their side (hello, tingly arm in the mornings). Over time, may lead to damage that is responsible for carpal tunnel.

While side-sleeping might exacerbate these specific conditions (and possibly others, depending on a health care provider’s assessment of your needs), there’s probably no need for a healthy adult to boycott left-side sleeping or side-sleeping in general. In some cases, side sleeping is even recommended. It can take pressure off the spine for people with back pain. Left-side sleeping is also the best position for pregnant women, because it prevents the baby from squashing the veins near the mother’s heart (which can happen if a pregnant woman sleeps on her back) and from squashing her liver (which can happen if she sleeps on her right side). And of course, no matter who you are, sleeping in a position that allows you to get sufficient and peaceful rest is a key factor in your overall health. So, it’s probably not worth it to lose sleep (literally!) over the position you nod off in.

However, if you’re still concerned about sleeping on your left or are waking up in discomfort, a trip to visit a health care provider might help you figure out exactly what your body needs. Hopefully this helps you get back to counting those sheep rather than fretting over left-sided sleep!

Last updated Jul 10, 2015
Originally published Jan 21, 2011

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