The Sleep Cycle: Still Mostly in the Dark

Left image: How much of your night is spent in each phase of the sleep cycle; Stage 3 (N3/SWS) sleep is considered the most restorative and makes up about 20% of young people’s sleep, but as little as 10% of seniors’.
Right image: A typical young person’s five nightly sleep cycles; note that almost all N3/SWS sleep occurs in the first two cycles (the first three hours) of sleep.

As with most pseudosciences, the ‘medical’ research on the connection between ‘good’ sleep and good health is mostly anecdotal, reinforces ‘conventional wisdom’, tends to confirm the researchers’ hypotheses (research that doesn’t confirm their hypotheses generally doesn’t get published), is subject to multiple cognitive biases, and fails to meet rigorous scientific standards. In other words, it’s mostly just opinions.

The other problem with sleep ‘research’ is that there’s not much money to be made from it, so it’s underfunded relative to its importance to our health. And in any case it’s hard to test hypotheses about sleep since testing generally requires disrupting people’s normal sleep habits. And of course it’s almost impossible to compensate for all of the factors that might provide a better explanation for the test results, many of which the test subjects probably aren’t even aware of. For example, older people tend to overrate their sleep quality (compared to what researchers found) because they just expect poorer quality sleep in old age to be ‘normal’.

With those caveats, I’ve been looking at what we know about something called N3 (third-stage non-REM) sleep, also known as slow-wave sleep (SWS). My interest stems from some modestly-convincing evidence that this, the deepest stage of sleep, is the stage mostly associated with the body’s restorative systems — secretion of human growth hormone (to repair and replace worn cells and tissues) and a shift in the autonomic nervous system from a sympathetic (“fight/flight”-ready) state, towards a parasympathetic (“rest and digest”) state. It’s also allegedly the state most associated with the immune system’s self-healing processes. And some new research suggests a shortage of N3/SWS sleep correlates with a higher risk for memory loss and dementia.

I’m not sure I buy this — there’s a lot of room for confusing correlation with causation here — but I’ve noticed in my retirement years that I feel less ‘rested’ in the mornings than I used to, and specifically I hardly ever wake up in the mornings feeling like I’ve had a really great night’s sleep, which used to happen quite often. So I thought it was worth looking into. Apparently this feeling of having had a good night’s sleep correlates with the amount of N3/SMS sleep achieved.

I started with nutritionfacts.org, since I trust Michael Greger’s skepticism about the quality of much medical research, and his insistence on relying only on the most credible reports and meta-analysis. Not surprisingly, that review didn’t turn up any great surprises (with the exception of the effect of pistachios, noted below).

So I read some other meta-analyses from relatively credible sources not linked to the “sleep industry” or obvious medical quacks. Here’s the unexciting consensus of how to maximize your SWS “deep” sleep:

1. sleep in a dark and quiet room (sleep masks and earplugs work better than white noise machines)
2. keep your bedroom between 18-21ºC, and well ventilated
3. maintain the same bedtime every night, and aim to wake at the same time every morning
4. get 90 minutes of moderate or 40 minutes of vigorous exercise a day; and exercising late in the day is fine
5. no screens in bed, or less than an hour before sleep (and there is limited evidence that blue-filtering glasses work)
6. eat foods rich in antioxidants, avoid foods that are inflammatory (saturated and trans fats and cholesterol), and avoid heavy meals just before bedtime
7. get out of bed if you can’t fall asleep or if you awaken, rather than just lying there; in fact leave the bedroom and do something else (not involving screens) until you feel sleepy again
8. occasional daytime naps are OK but avoid a regular habit of them
9. don’t use your bed just for lounging
10. eat just two pistachios if you’re suffering from insomnia or jet lag, one to two hours before sleep; just two pistachios has as much natural melatonin as a full dose of melatonin pills
11. drink 6 eight-oz cups (1.5 litres) of water (men 8 cups — 2 litres) during the day, but minimize liquids in the evening; that will keep you healthily hydrated but minimize overnight awakenings to pee
12. do about 5 minutes of Progressive Muscle Relaxation in bed just before sleeping, starting with your foot muscles and working up: inhale, contract muscles for 5 seconds, exhale and release, relax for 10 seconds, then move on to the next muscle group

Makes sense, I suppose. The problem with most of these findings is that they relate to a shortage of overall sleep (insomnia), rather than a shortage of N3/SWS sleep. As we age, our average hours of N3/SWS sleep drops by more than half, even when taking into account the sleep-affecting chronic illnesses and geriatric conditions that are more prevalent in older people.

What’s going on here? If N3/SWS sleep is when our body regenerates its cells and tissues, and restores its nervous and immune system, shouldn’t older people be getting more of this rather than less? And does it have something to do with the fact most N3/SWS sleep tends to occur in the first three hours of sleep, and the fact that older people tend to get up earlier in the morning, and wake more often and for longer periods at night, but often don’t go to bed that much earlier at night to compensate?

Another obvious question is whether frequency of sex in the evening improves your ability to fall asleep (hopefully afterwards) and the quality of that sleep. One study suggested that partnered sex with orgasm did modestly (but only by about 15%) improve both these things, while neither masturbation (with or without orgasm) nor sex without orgasm did (and the results were the same for men and women). Pretty subjective data, though. It basically relates to the type and volume of hormones that either promote or inhibit sleep, that are produced during different ‘kinds’ of sex.

My speculation is that part of the answer to these questions is the gap between perceived sleep quality and actual sleep quality, specifically the duration of N3/SWS sleep. Several studies suggest, for example, that exercisers often will report no improvement in sleep quality, while monitoring devices suggest they have achieved significant improvements. If the exercise makes your muscles stiff, you might feel unrested in the morning even though that exercise significantly increased your N3/SWS sleep.

I’d also speculate that getting up (eg to pee, or to deal with aches and pains) within a couple of hours of going to bed might prevent you from getting that essential N3/SWS sleep that mostly occurs early in your sleep. Rather than just ‘number of awakenings’ during the night, it might be worth tracking the timing of those awakenings, and studying how to shift those periods of awakening to later in the night, after the benefits of N3/SWS sleep have already been achieved. Or alternatively, perhaps, finding a process for ‘resetting’ your sleep cycle after awakening, so that you go more quickly into N3/SWS sleep.

Related to that, one might surmise from the research that ‘sleeping in’ (eg on weekends) to make up for a late night (or a week of late nights or bad sleep) might not help much, since later cycles feature less N3/SWS. I’ve found myself that when I just ‘sleep in’, the extra hour or so doesn’t seem to help my overall sleep quality, but if I get up, do something uncomplicated, and then go back to bad, the extra sleep seems much more beneficial.

My final speculation would be that it’s the quality of sex (including solo sex) that determines its benefit for your subsequent sleep. Not rushed, not done “just so I can get some sleep”, not feeling awkward or guilty, not an attempt at catharsis to address some stress or unhappiness in your life. I can’t imagine any sex that is really fun not having a positive effect on your mood, your body chemistry, and your sense of relaxation when you turn out the lights, which I think inevitably is going to improve the quality of your subsequent sleep.

The researchers may never be able to figure it out, but our bodies know what they like, want, and need. Listening to them might be the best advice for improving both the joy and the benefits of our sleep. And if that reduces the risk of cell and tissue breakdown, the diseases of chronic stress, immune system dysfunction, memory loss, Parkinson’s, and dementia, so much the better.