There is a lot of info here and much I agree with but without reading the whole thing a few things I noticed that I disagree with:
1) the fatal result of rats being tortured to deprive them of sleep seems to have been traced to oxidative stress in the gut (there was an article on this here not that long ago)
2) while I don't have an easy reference, a number of studies have found that even strenuous exercise before bed does not seem to impair sleep. As with everything sleep related there could easily be lots of individual variation but in general I don't think it usually causes trouble.
3) the author seems to consider free running sleep entirely posistive, however I think it is likely to cause circadian issues in a number of people who try it and may be quite dangerous. I think in my case going from a sleep deprived state to free running sleep (in an attempt to deal with insomnia) induced non-24 (it may be that non-24 has both a genetic susceptibility and a trigger event and that once triggered is essentially irreversible). In my case it also seems that there is an issue with internal coherence of the circadian rhythm with different parts of my body proceeding on different scheduled and rarely synchronized, leaving me disabled with memory issues and fatigue. So I encourage everyone to be careful when making changes to sleep schedules. For someone who already has a circadian issue it seems often better to sleep on the delayed or shifting schedule, but few people can do that without significant disruption caused by interacting with the rest of the world and there may still be some issues, at least for some people, due to being awake at night.
4) I think alarm clocks can in some cases keep a healthy circadian rhythm synchonized with the sun. Maybe consider them more like a prescription medication than smoking, try to avoid if possible but if using one can help you keep a healthy circadian rhythm then it seems likely to be healthier than a disrupted circadian rhythm. In my experience, when you wake up seems to be more important for setting the circadian rhythm than when you get to sleep.
I don't think there is anything natural about such a rigid "circadian rhythm".
Its a leftover from feudal / agricultural society where you had to get up to do different things on the farm _all day_ until you where so tired you crashed and slept for 8 hours. Nothing natural in that.
I totally agree that "getting up early" can have its benefits, and so can an uninterrupted 7 hours - but the body is built to get up in the middle of the night, do stuff, then go back to bed, get up again, scavenge, build, talk to someone, then take a nap with your family/tribe etc.
As long as you follow the inner rhythm, and can zone-out and relax, you are probably most healthy going through various states multiple times a day, from intense focus, to alert, to way more relaxed than anyone are today.
This is in stark contrast to the toxically over-caffeinated over exerted extremely long days where you never really go through any different "mindstates" but just "plough through" until you crash - and then think that you need 8 hours and to get up early - no you only need that because you are abusing your body. Also you are missing out on so many states that make life worth living, ie the liminal hypnagogic state, the absolutely magical hypnopompic state, wonderful actual alpha-brain relaxation etc.
This is also why people become sad, superficial, loose connection to the magic of existence and ultimately become sociopaths constantly seeking superficial hits because they have no space or time for the liminal states.
While I haven't done extensive historical research on sleep habits, the limited history that I have read makes me doubt your assertion. I think being up for a bit during the night and siesta are both things that can potentially happen while keeping a healthy circadian rhythm, but I don't think they are necessary for a healthy circadian rhythm. My impression is that siesta is a very common human practice with a boiological basis, but I'm not convinced that the same is the case with being awake for a while at night.
I suspect the human body can adapt to many different schedules and some will work better than others for each individual. My sense is that the most important thing is keeping a very regular schedule to make sure that when we are sleeping we are fully asleep. For me being awake at night seems to independently cause trouble and I suspsect this is likely true of most people, but it might not be the case with everyone. Even so, I suspect an irregular sleep schedule is much worse than being awake at night.
How did you arrive at this opinion? Are there studies that compare a polyphasic sleep schedule to a fixed sleep shield that you've come across? I am mostly polyphasic because of insomnia and have been for many years so I'm interested in reading more about it
2) while I don't have an easy reference, a number of studies have found that even strenuous exercise before bed does not seem to impair sleep. As with everything sleep related there could easily be lots of individual variation but in general I don't think it usually causes trouble.
I think this might come down to heart rate. I've found that when I bike home at like 10 pm from somewhere say 30 minutes away, I'm fine now with sleep but when I first started biking back from somewhat far places I couldn't sleep well all night.
https://supermemo.guru/wiki/Circadian_phase
I follow this graph from him and I've found that if I exercise at the time marked as "sports" even 1 hour isn't enough for my heartrate to lower which leads to a worse siesta nap. I'm hoping that long-term as I get more aerobically fit it becomes less of a problem.
More generally, I don't think the argument is that strenuous exercise impairs sleep. More that it effects your circadian rythm. iirc from talking to Woz, for him, sports make him more tired and bring sleep phase earlier and I think my experiences are somewhat similar, though both of us exercise in late morning.
Regarding 1: Sleep loss lethality is caused by gut ROS in mice and flies [1]
> ...researchers demonstrate in flies and mice that sleep loss leads to an increase of reactive oxygen species (ROS) in the gut, and that neutralization of ROS can prevent oxidative stress and prolong the lifespan of sleep-deprived flies.
Various biological systems seem to have recovery mechanisms associated with the sleep cycles. These cycles are measured using EEG devices but all the major SmartWatch vendors are adding predictive machine learning algorithms to generate the equivalent sleep cycles using optical heart rate data.
Continuous sleep cycle tracking might provide crucial insights related to optimal health.
Lots of companies have products with claimed effects or measurment of sleep but personally I suspect they are almost always complete BS. I've used a recording pulse oximeter when sleeping a number of times and the pulse seems to reliably predict when I get to sleep but nothing else, not even when I am awake vs. sleeping. IMO, there is no possible way a pulse measurement could replace an EEG. I am also not convinced that sleep tracking would be helpful at all for most people, at least beyond keeping a log with a basic estimate of how much sleep you think you got and how long you were in bed. And even that seems only rarely useful, mostly because I've found it isn't obvious when I've had a month where I slept quite a bit less than usual. So maybe the helpful part is putting it in a spreadsheet and doing some statistics. But for most people I would guess that doing any sleep tracking would cause some disruption and be more harmful than helpful.
I forgot to comment on the following important point:
> the pulse seems to reliably predict when I get to sleep but nothing else, not even when I am awake vs. sleeping
My experience with the Zeo made me realize that predicting sleep vs wake is hard to do. The modern multi-sensor devices tend to use the accelerometer derived movement together with historical sleep times to predict this. The early Fitbit devices tracked sleep with the motion sensor alone. In the middle of my normal sleep cycles, if I listen to a podcast or read from a smartphone/eReader while remaining mostly motionless, both the Zeo EEG and the Garmin PPG derived EEG will interpret that time as REM sleep.
I wonder if the professional sleep labs can accurately detect the difference? The true test will be when sensors/algorithms in casual activity trackers can detect when we nod off or nap during normal waking hours.
See Garmin Health Announces Sleep Study Results [1].
I used a Zeo [2] mobile for a few years and I thought I had a good feel for what my sleep cycles tended to look like.
I bought a Garmin VivoSmart last Black Friday mostly to try the SpO2 and sleep tracking. I shared your skepticism but, anecdotally, the sleep cycles are as good as what I would get from Zeo.
Hmm... 70% agreement in an unpublished study funded by the company vs a device that is itself maybe 90% agreement with lab PSG. Better than I expected, but I wonder if it is just due to many sleepers having quite predictable stages. "Figure 4 shows the worst result of the cohort (55 of 55), with an accuracy of 49.9%. Note that this user self-reported having a sleep disorder."
> I wonder if it is just due to many sleepers having quite predictable stages
That is what I wondered. The Garmin reports my deep sleep in ways that don't match predictable patterns and do approximate times of random events like being woken by animal noises or sirens. Its much better than I expected and I can see it getting much better with the incorporation of additional sensor/external data.
> 2) while I don't have an easy reference, a number of studies have found that even strenuous exercise before bed does not seem to impair sleep. As with everything sleep related there could easily be lots of individual variation but in general I don't think it usually causes trouble.
Hopefully.
These days, with all this working and staying at home, I'm sure for a lot of people their most strenuous exercise is just before going to sleep.
> In my experience, when you wake up seems to be more important for setting the circadian rhythm than when you get to sleep.
That's my experience too, however I think it is misleading, for some people, to describe circadian rhythm as a single daily clock.
In my experience it's more like:
1) There are a small number of distinct rhythms. When these are aligned, sleep is more refreshing, and they feel like one larger coherent process. When they are unaligned, sleep is less refreshing, and the awake time has a number of "different kinds of tired" intervals, as varies cycles that would ideally be during sleep occur during awake time instead. When severe, it's difficult or impossible to work during these intervals, even when getting plenty of sleep as well.
"Different kinds of tired" means things like tired muscles, or tired mind, or difficulty focusing, or poorer temperature regulation, or... Basically different processes in the body, which could all be conflated as "tired" yet are distinct from each other.
One of the most annoying is feeling very sleepy and needing to lie down, yet not falling asleep because it's the wrong kind of tired for actual sleep. After hours of that, maybe the right kind of tired will happen, at which point actual sleep happens. When these cycles are misaligned the overall process can take most or even all of the available 24 hours a day; it is very difficult to hold down a job when this is a regular occurrence.
2) The overall circadian cycle sometimes breaks up into pieces, like those 24 hour mechanical timers with a separate bit of plastic for each 15 minutes, which can be set to one long interval or more than one shorter interval.
As many other people point out, regularity is good for maintaining a strong circadian rhythm. I find that includes these multiple intervals: They seem to appreciate consistency too. I also find waking earlier/later (e.g. due to the sun, work, clocks etc) doesn't always drag the whole 24 hour cycle forward or backward; sometimes it seems to create a new interval and allow an old one to shrink or fade.
> trigger event and that once triggered is essentially irreversible
I had a trigger event which I can trace back specifically to age 15: Working on school coursework in bed in the early hours of the night. It's not really a single event so much as a time period of a few months.
Up until that point I had reasonably regular sleep.
Ever since then I suffered from essentially chaotic and unpredictable sleep times for about 20 years.
No amount of "discipline", from school, jobs etc., fixed this. It just meant I was tired, and late getting to work a lot, because the alternative is to be on time but too exhausted to be useful, a real dilemma.
Eventually after about age 35 it started getting a bit more regular. But it's not great, and I have to be very conscious about managing sleep.
A challenging aspect of this is I'm far more productive if I decide to pull an all-nighter than if I remain disciplined about sleep. I have found with great consistency that in a well-chosen all-nighter, I've often got more things sorted out than a month of regular work. It's frustrating; I would like to do that in the daytime! If I'm disciplined and avoid doing that, months can go by with only "mundane" levels of productivity, and it's disappointing knowing I'm capable of more. As a decent programmer, I'm lucky that "mundane" is still good, but it's not what I can do at my best. I'd still like to crack this problem but I haven't found a solution yet.
What you say about the intervals makes sense to me, and related to rajlego's comment as well it seems like major changes in activity level or timing take some adjustment.
I know what you mean about "different types of tired". It is rediculous how many different varations of being tired there are if you have serious sleep issues. I have the same thing about feeling completely exhausted and what I could only call tired but not being able to actually sleep. I have learned a bit over the years (I'm about 40) to tell when it is actually possible to sleep but I am never sure. This is the kind of thing I want to warn people about as well as the non-24 when people talk about trying unusual sleep schedules; it really can mess you up quite a lot if things go badly.
I have also noticed that every few years there seems to be a significant shift in how I sleep and I've heard similar from others with various sleep issues. I suspect it might also be the case for most people and seems like it would fit well with your interval descripiton.
I had at least two periods of severely disrupted sleep lasting years in my first couple of decades of life but didn't end up with non-24 until I tried free running sleep. Although thinking about it a bit more it wasn't fully free running for a longer period but more trying to advance what had become a very delated sleep schedule (mostly by means of not using an alarm clock until I was back on a schedule of sleeping during the day). It is possible it would have happened anyway in my case. And the "generally disrupted sleep" aspected that I still have due to insomnia and circadian desynchronization seems worse than the non-24 part, but still not having non-24 even with the other sleep issues would be preferrable to me. It sounds like you have a milder version of what I have.
I also sometimes have noticed that I am most alert and productive not long before bed, although for me most often a similar thing happens early afternoon when I am waking up before 9 (and I personally seem to do best waking up at about 7am). My guess is that it happens before bed due to the process that keeps us alert right before bed that somehow is extended, my guess is that is related to having not previously reached a similar level of alerness earlier in the day. I have been meaning to look into that process in more detail but haven't done it yet.
I've also been thinking that for me at least one of the major issues is that the process of waking up is not working correctly. When I get less sleep than usual I can these days sometimes avoid advancing my sleep schedule but not always and even not sleeping at all does not usually make it easier to get to sleep early the next day. But it does make it easier to sleep longer once I do get to sleep. Maybe once every few years or so something briefly happens in the morning right as I am waking up that feels like rapidly altering between being asleep and awake for a few seconds causing a distinct feeling and I am always much more alert than usual that day.
Have you used melatonin at all? I find that oral or sublingual melatonin cause me to wake up a couple of hours after I get to sleep and not be able to get back to sleep (melatonin patches do not cause this but do not help at all getting to sleep, only staying asleep longer). This happens even if I take a small amount of melatonin a few hours before bed, meaning it should all be out of my system before I even get to sleep. I wonder if there is a "spring" aspect to the wake up mechanism such that it can be improved even before getting to sleep.
1) the fatal result of rats being tortured to deprive them of sleep seems to have been traced to oxidative stress in the gut (there was an article on this here not that long ago)
2) while I don't have an easy reference, a number of studies have found that even strenuous exercise before bed does not seem to impair sleep. As with everything sleep related there could easily be lots of individual variation but in general I don't think it usually causes trouble.
3) the author seems to consider free running sleep entirely posistive, however I think it is likely to cause circadian issues in a number of people who try it and may be quite dangerous. I think in my case going from a sleep deprived state to free running sleep (in an attempt to deal with insomnia) induced non-24 (it may be that non-24 has both a genetic susceptibility and a trigger event and that once triggered is essentially irreversible). In my case it also seems that there is an issue with internal coherence of the circadian rhythm with different parts of my body proceeding on different scheduled and rarely synchronized, leaving me disabled with memory issues and fatigue. So I encourage everyone to be careful when making changes to sleep schedules. For someone who already has a circadian issue it seems often better to sleep on the delayed or shifting schedule, but few people can do that without significant disruption caused by interacting with the rest of the world and there may still be some issues, at least for some people, due to being awake at night.
4) I think alarm clocks can in some cases keep a healthy circadian rhythm synchonized with the sun. Maybe consider them more like a prescription medication than smoking, try to avoid if possible but if using one can help you keep a healthy circadian rhythm then it seems likely to be healthier than a disrupted circadian rhythm. In my experience, when you wake up seems to be more important for setting the circadian rhythm than when you get to sleep.