As a nation, our sleep habits are far from perfect. More than half of adults in the UK sleep for six hours or fewer each night, according to an Aviva survey, while just 17% of adults get a desirable eight hours. And we’re becoming obsessed with it: by next year, the global sleep aids market is projected to be worth $80.8bn.

Like many of us, Ruth Walker uses her fitness tracker to track her sleep. But recently, the 32-year-old has been reconsidering that choice – considering whether her anxiety about getting enough sleep is becoming more of a problem than a lack of sleep itself. “When I’m struggling to sleep and trying to relax, it stresses me out knowing the time is being logged – and that way of thinking hinders my sleep even more,” she says.

Walker first started tracking her sleep two years ago, and routinely checks not just how long she’s sleeping for, but also the sleep stages she’s entered each night, and the overall quality of her rest. The results don’t always correspond with her feelings on waking, however. “Sometimes I wake up feeling refreshed and that I had a good night’s rest, only to be told by the app I didn’t get as much sleep as I thought,” notes the marketing manager from Newcastle. “It makes you question – do I feel refreshed?”

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When the US website Cnet asked more than 1,000 readers about their tech habits in autumn 2018, 30% of respondents said they used some form of sleep tracker or sensor every night. A report by Future Market Insights suggests Western Europe is the second most dominant market for wearable sleep trackers and that the market is expected to continue to grow between now and 2028.

But as the use of sleep trackers has become more widespread, so too has the idea that actually, they might not be the best thing you can wear to bed. In 2017, a report published in the journal of Clinical Sleep Medicine suggested that sleep trackers may reinforce sleep-related anxiety or perfectionism for some patients – a condition dubbed ‘orthosomnia’ by the authors.

Kathryn Pinkham, founder of The Insomnia Clinic, has witnessed that need for perfection in practice. “What we see is that the anxiety around not sleeping well has been exacerbated by using a sleep tracker,” she explains.

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The need to record and monitor sleep is curious, argues Pinkham. “Why bother tracking it unless that in some way is going to fix it? People will know if they’ve slept badly, why do they need a tracker to tell them?”

Yet the reality is that many of us do want to see the numbers. That’s a concern for Maryanne Taylor, founder of The Sleep Works. “I worry that the flip side of that [sleep tracking] is the overwhelming obsession of having to achieve X hours of sleep a night,” she says.

Thirty years ago, the opposite was true: in the eighties there was huge bravado about who could sleep least – famously, Margaret Thatcher is said to have slept for just four hours a night. But more recently there has been growing awareness that having too little sleep just isn’t good for you – and has been linked to all kinds of negative health implications. “The tide is turning,” says Taylor. “I think fitness trackers are part of that. But also there’s been this surge where finally people are recognising mental health and general health, and how sleep fits into that.”

Negotiating all that information is not straightforward – sleep is the the subject of many thousands of articles, bestselling books and endless studies – but throughout it all, we’re routinely told we should be getting eight hours a night. And the fixation on one number might not be helpful. 

The idea we have to be asleep for eight hours in order to have a good night’s sleep, is a myth, argues Taylor. Sleep is very individual: ”We’re split into long sleepers and short sleepers, and some people do feel they need to have eight hours but some people are short sleepers and achieve exactly the same in terms of their sleep needs on less than that,” she says.

“We see it everywhere: our optimum health and optimum sleep, it has to be this and it has to be that – it’s a dangerous game. And that’s where this obsession starts to grow.”

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As we’ve become more interested in sleep, so our ability to track how “well” we’re doing it has also grown. Initially, people obsessed over the number of steps they did. Now the hours and minutes that your fitness tracker says you’ve slept for has become equally important. 

Francesca De Franco, 40, from Banstead, Surrey, first started tracking her steps when her husband bought her a fitness tracker two years ago – when she noticed it also tracked sleep, she decided to give it a go. The tracker vindicates her belief that she’s always had bad quality or not enough sleep, she explains. “I check it as soon as I wake up and then I’m really disappointed when my sleep time is under six hours, which it frequently is.”

Pinkham estimates that roughly half of her clients have used a sleep tracker at some point. Often, before visiting her clinic, they will have tried to fix their sleep problem by introducing a few sleep hygiene measures (like giving up caffeine), before progressing to tracking their sleep through a device or app on their phone – which then becomes the first thing they check in the morning, every single day. “It’ll tell them that they’ve had a terrible night’s sleep,” she says. “[This] causes anxiety about the day ahead – so rather than listening to how they actually feel, they decide they feel tired and will maybe cancel a meeting or a social event that night.”

In short, people are listening to the results of a sleep tracker rather than what their bodies are telling them. And here lies the problem. “It increases anxiety about sleep quality, and it definitely contributes towards the mental health aspect of sleep problems because it’s playing on someone’s mind,” Pinkham explains. “If they read that they didn’t get any deep sleep last night, that will affect how they behave. It’s very much a self-fulfilling prophecy – if you believe you slept badly, you will act like someone who slept badly.”

And that can be particularly the case when people are exhausted and at their most vulnerable. For new parents, it could definitely become a source of anxiety, says Vicki Psarias, 38, author and blogger at Honest Mum. “I feel if I was a new mum, tracking sleep could contribute to me feeling worse at a time where sleep deprivation is at an all-time high and how much sleep you’re getting can become all-consuming.”

The extent to which sleep or fitness trackers accurately monitor sleep is disputed. Some claim to monitor different stages – awake, light, deep and REM – while others promise to measure heart rate, levels of movement, breathing rate and blood pressure. But the National Sleep Foundation suggests they are limited in their usefulness – and Taylor agrees. 

“The technology within them isn’t smart enough to give an accurate reading,” she argues. When a person is asleep they will transition through sleep cycles, moving between light sleep and deep sleep, and then back into light sleep. “But the stage of light sleep and the stage of wakefulness on a sleep tracker reads almost identically,” Taylor explains. “So the technology isn’t smart enough to read properly between light sleep, which is a key part of our sleep cycle, and an awake state.”

People who look at their sleep trackers in the morning might see large periods of time where they were ‘awake’ and then believe they didn’t sleep well. “If they were to do a proper monitor in a sleep lab, they would have a very different result,” Taylor adds.

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Dr Rebecca Robbins, co-author of Sleep For Success and a researcher at NYU Langone Health, argues that we can’t yet say for sure whether sleep trackers are causing more harm than good – although she does note that scientific literature has shown a heightened level of stress around sleep among insomnia patients . “Patients walk into their room, they’re nervous about being not able to fall asleep and then that nervousness translates to poor sleep,” says Dr Robbins. And sleep trackers could make that pressure worse. 

They also can’t help you fix any problems you think you may have. Seven years ago, Jo Norton, 28, made lots of changes to try and improve the quality of her sleep: she tried using a phone app to track her sleep, wearing an eye mask to block out light, watching calming videos before bed, following guided meditation and was a dedicated user of lavender oil. She was still exhausted.

Three years later she went to an orthodontist who she says spotted her sleep disorder within minutes. “I couldn’t pinpoint what was happening in my sleep or why I was so tired,” she says. “When I was eventually diagnosed with UARS (upper airways resistance syndrome) and saw my blood oxygen graphs, I could see why my sleep was so disrupted. An app was never going to show that.”

She adds: “It sounds a bit dramatic but my orthodontist saved my life.”

If you are a poor sleeper and you’re finding that sleep apps aren’t giving you much insight, consider seeing a professional who can help determine whether there’s an underlying cause such as sleep apnoea, stress or anxiety. And if you actively believe your sleep tracker is causing you anxiety about sleep, it might be time to pull the plug. 

Mary Baird-Wilcock, 41, a podcast host and business coach based in Nottingham, had to ditch her sleep tracker after she realised it was stopping her from nodding off. She was using a sleep app on her phone, which involved putting the phone under her pillow each night. “I have zero willpower,” she says, “so as soon as I laid my head down, knowing full well my phone was under there, if I didn’t get to sleep within 10 minutes I would instantly reach for my phone and watch another episode of Schitt’s Creek or RuPaul’s Drag Race.”

The result? Less sleep. “I knew I needed to remove my phone from my bedroom, ignore the app and simplify down to get back to basics to increase my sleep health,” she adds.

Listening to your own body rather than to an app is a good first step to better sleep, says Taylor. ’Before you reach for the sleep tracker first thing in the morning you [need to] consider yourself – how do you feel? If you give yourself the opportunity to assess yourself without the tracker results, you give yourself a bigger picture,” she adds.

Even bigger picture, we need to stop obsessing over sleep full stop. The eight hour rule isn’t something to live by and people should instead be working out what their optimum amount of sleep is – in other words, how much sleep they need to not feel tired and groggy, to feel alert and awake. Avoid comparison, too. “Your sleep and your friend’s sleep isn’t going to be exactly the same,” adds Taylor.

For Ruth Walker, struggling to reconcile her tracked sleep with her own experience of that sleep, there’s a middle ground. Convinced that her tracker isn’t entirely accurate, she’s continued using it but treats the results as a baseline. “I think not knowing [the sleep data] may actually help some people,” she muses. “Then there are others for whom knowing the precise figure – especially when it’s over seven or eight hours – will feel better.

Now she mainly uses her tracker for exercise: “The sleep info is just something I take with a pinch of salt,” she says. “I would consider taking it off if I was having a bad patch of poor sleep to help me chill out more before bed.”