Light sleep. Deep sleep. REM. Circadian rhythms. The science of sleep is vastly complex, and something I've only started paying attention to.
I can tell you right now that I'm not a great sleeper. I don't suffer from insomnia or any other sleep-related illnesses (that I'm aware of), but when it comes to sleeping at the right time, consistently having a good night's sleep, and waking up feeling refreshed and energised - I definitely fall down. This is partly down to being a bit of a night owl, part down to ignoring the better advice of others ("Eight hours a night is optimal, don't you know"), and I expect some other factors I haven't yet realised. I often feel lethargic during the days, and restless during nights, and I know I can improve.
Which is why I've started this sleep diary, following in the footsteps of my colleague James Stables and his journey of training for a marathon by heart rate. For me, the quest is to discover what makes for a good night's sleep, how I can improve the quality and consistency of my sleep, and what technology can help get me to my destination.
And already I've hit my first hurdle: everything I thought I knew is wrong.
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I didn't want to go into this blindly, so I called on some expert advice. Stanford University's Center for Sleep Sciences and Medicine is renowned for the quality of its research, so I phoned Jamie M. Zeitzer, assistant professor at the center's Department of Psychiatry and Behavioral Sciences, to ask for some help.
To start, I wanted to understand what I should be looking for; what actually makes a good night's sleep. Turns out, it's a lot more difficult to answer.
"It's the issue of sleep quality and what exactly that means," said Zeitzer. "For all of these different functions sleep provides - memory consolidation, housecleaning the brain, changes in energy distribution - we have no ability at this point to measure how well sleep is doing in any of these objective functions. All we can do is measure outcomes, like if you don't sleep enough you don't perform as well. And we can measure subjectively about sleep." - by which he means you can ask someone how they slept last night, and they'll have an answer.
The problem comes with qualifying those answers. Zeitzer tells me that the department recently measured the sleep of 1,500 participants in a large study using machine learning and data analytics. When it came down to it, only around 15% of variability could be explained. "We basically found there is nothing we can pull out of the data that tells us anything about how you're going to answer the question 'How did you sleep?'."
How much people sleep doesn't seem to make a big difference in their subjective response, said Zeitzer, unless you get chronic withdrawal of sleep - that can be seen to lead to cognitive deficiencies.
Sleep efficiency, he said, is a better indicator for accounting how people feel the next day, but even that doesn't account for an awful lot. "I have a feeling, although this is not based on any specific science, that it's going to differ between people."
So what does this mean for all the devices that promise to monitor and help improve our sleep? And for my testing? Zeitzer dismissed much of the feedback as "nonsense" based on very little substance.
"The main problem with devices is that they don't ask you how you slept, they tell you how you slept. If you only sleep six hours, but you're one of the people on the bell curve who only needs six hours, that's not going to be bad."
Zeitzer said that his team even tested waking up at different times of the sleep cycle - a feature implemented in some devices and apps - but it didn't make a difference on the general population level. In any individual might it matter? "Sure," he said, but he believes it won't cut across large swathes of the population.
Having a regular wake-up time means the body will start to naturally anticipate when it's time to start waking - and that's something I can apply to my own research - but that doesn't guarantee I'll feel revitalized the following day. "Some people might respond better to waking up at a certain state of sleep, some people might respond to having a more efficient sleep."
Zeitzer said that, by his last count, there were more than 100 devices commercially available for tracking sleep, with most featuring the same triaxial accelerometer tech.
"We've been using this in the field for 25 years to monitor sleep-wake patterns, and there are publicly available validated algorithms you can use to impute sleep vs wake from triaxial accelerometer data. The fundamental technology is a well validated concept, and so it's very cheap and easy to throw one of these things in a watch and say it's validated."
But Zeitzer said these accuracy measurements can often be "deceptive", as most of the time you're in bed you're asleep anyway, and so it's easy to say a device has a high accuracy of detecting when you're awake or not. It will be interesting to test devices alongside each other and see how their accuracy compares to each other, and to my own recollection of how well I slept.
With all this in mind, it's obvious that tracking and improving my sleep is going to be a very individual journey that won't be as simple as strapping on a device and sticking with it. There's also a lot of nonsense out there, and to improve my sleep I'm going to need to pay very close attention to what my body is telling me, and see if and how tech can guide me at all.
Even if it's a challenge to get an authentic analysis of how well I was sleeping, some of these devices could help me establish better habits.
I asked Zeitzer what I need to consider to make this a useful test. "You want variability. If you just have good nights of sleep, that's not going to tell you much."
I suppose that makes sense. Zeitzer also told me I should put myself in situations where I have poor quality sleep. "And the question is, does the device pick up that was wrong in your behaviour? Or can it pick up something that perhaps can compensate? For example, every time I go to sleep, I miss my window of opportunity, am I up for three hours and have a bad night's sleep"
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Beyond that I should see if these devices pick up alterable things. And if I follow their advice, does it change anything? Zeitzer is very interested in some new startups on the scene that are looking to monitor both sleep and environmental variables. He believes monitoring environmental variables could be more important for improving sleep than tracking depth and length of the sleep itself. So it will probably be worth looking at things like air temperature and quality too, and seeing if that has an effect on my sleep.
But my first task is to test out a range of sleep-tracking devices together and see how the data compares, and whether they throw up anything useful. From there I can hone in on the ones I believe are providing the most helpful information, and see whether any of it can start sleeping better.
Right, time to get some Zzzs. Join me again next Monday to see how successful my first steps are.