What is the healthiest position to sleep in?

05 July 2016



What is the best healthy pose to sleep in? It is said that left side is not desirable because of the heart beating there. Is it be true? Are we are expected to lie on the back or belly? I believe there were a lot of research in this area. I realize that everybody sleeps as they like it or at least depending from their psychological state of mind but the whole aspect seems intriguing to me. Waiting for the answer, love your wonderful program.


Kat Arney put this to fellow Naked Scientist Chris Smith...

Chris - Depends who you are talking about because if you are talking about little babies then there's one rule for them which is - and there's been a very successful campaign in recent years called Back to Sleep, because very many studies have now shown beyond doubt that the risk of things like sudden infant death syndrome, which is otherwise known as cot death - terrible situation - that risk is lower in babies that are put to sleep on their backs. Once they get older and can turn over and do all that kind of thing, it's different. But for very young babies, putting them on their back is definitely the best position to sleep in. It's associated with fewer bad outcomes. 

What about if you're pregnant and expecting a baby? Well, because you end up with this very large mass - especially towards the end of pregnancy - I fortunately haven't had to put up with this but my poor wife has - you end up feeling a bit like an HGV driver in what she dubbed the, "I just want it out" phase. It's a very big abdominal pressure and big blood vessels have to run through your abdomen to carry blood from your legs and the lower part of your body, back up towards your heart. The main blood vessel, the vena cava runs on the right hand side. Therefore, if you lie on your back, a lot of that mass in your abdomen is going to push backwards and squeeze down on your vena cava and that's going to reduce the flow of blood back to your heart, which means that your legs are more likely to swell. It means your cardiac output is lower. So you advice, if you're pregnant, sleep on your left hand side because that transfers some of the load away from where the big blood vessels are, meaning the blood can get back to your heart more easily.

Kat - But what if I'm not pregnant and not a tiny baby?

Chris - So, for your average punter, there've been a number of studies looking at this, actually. It depends whether or not you want to have vivid weird dreams.

Kat - I get those anyway. I think it's the Scotch!

Chris - it could be! Or the cheese! There's a study that was done about 10 years ago where they actually - and it was a small group of people, 63 odd people - and they asked them, "What were your dreams all about?" And they looked at how they slept. What they found is that the people who slept on their backs had the most soothing nights sleep. But people who slept on their right hand side tended to have the nicest dreams. The people who slept on their left hand side tended to have the most nightmares. It was 40 per cent versus 14 per cent, but - again - it was a very small study. That said, a big study from China - with thousands of people in it - seemed to corroborate the effect. But then there's the question of, what is best for your health long term? There was a very good study in the journal of neuroscience last year. It was by Helene Benveniste and she's a researcher at Stony Brook University in America. They were asking, "Well, what happens if we actually look at how the brain responds when you're asleep, and what's the role of sleep?" When you go to sleep, your brain cleans itself out. You have an entity called the blood brain barrier that cocoons your brain away from your blood and it keeps the brain isolated chemically from the rest of your body during your waking hours. But what that means is that, over the course of the day, lots of metabolites and rubbish build up in the brain, which contributes to you feeling sleepy. So when you go to sleep actually, a system called the glymphatic system kicks in and it flushes this stuff out of your brain and that's why you feel refreshed after a good night's sleep.

Kat - You've a had a good brain washing!

Chris - Exactly! But the question is, in what position is that most effective? Now we don't know in humans. They [the Stony Brook team] did their study in rats. Now, a rat that was on its front pooled some of their tracer molecules and showed the least good wash out of these metabolites. Rats on their backs, they had sort of intermediate levels of washout. The best position was on the side. This is done in rats so you've got to be cautious. It's a rodent study, but it does appear to hold water because rats have very similar brain anatomy to us, really. So, it looks like, to reduce your risk of build-up of muck in your brain, and that muck includes the muck that can cause Alzheimer's disease. Sleep on your side. That's the argument. Marian.

Marian - But weren't you saying, if you sleep on your left, you have nightmares?

Chris - Yes, a nice brain wash. You're having nightmares, that's right, but remember this is a small study and only 40 per cent of the people had some disturbing dreams. The people who slept on their fronts in the Chinese study, they dreamt about UFOs and other bizarre stuff. So, it could get even worse.

Kat - That's amazing. And of course, if you sleep on your back and you snore, you would just be poked all night, shut up. So a lesson for us all!


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