For those who like words: Animals that are most active at dawn and dusk are crepuscular, which can be further divided into matutinal (dawn) and vespertine (dusk).
I had a feeling you already knew it! But, if you hadn't left it out, I wouldn't have learnt matutinal when I made double checked I had the right word, so thanks for that :)
I don't understand how the darkness part of entrainment works. I'm in mediterranean, daytime duration ranges from roughly 16 hours in the summer to just under 9 hours in the winter. If that had major influence, it seems like it would just be messing the rhythm up.
But then, if it's only (or mostly) about morning sun exposure, daylight saving time would not be such a big deal (if you don't wake up at sunrise, which I guess most people don't?). The clock shifts, you wake up with an alarm clock an hour earlier, and then you immediately get sunlight exposure at waking time, just as you would if you traveled.
Maybe I'm out of touch and most people don't actually get up more than an hour after sunrise? But when the clock shifts forward in March, the sunrise is around 5:40 (shifting to 6:40 next day). If you get up at 7, you should be good.
I don't know if it's the combination of sunrise/sunset, but I naturally wake up significantly after sunrise (often 2-3h!) and DST still hits me quite hard. In fact, it seems to hit night owls much harder than morning larks.
One explanation could be that it's technically not "the first sunlight that hits you" in the chronological sense, but in relation to your own circadian rhythm. I.e. if I'm a nightowl and I wake up at 10am, using an alarm to wake up at 5am and getting into the sun wouldn't necessarily help. I would need the sunlight at 9-11am. Similar with sunset. Similar to wakeup, I get tired around 3-4h after sunset. But yea we don't exactly have a ton of data/understanding on how exactly it impacts people at that granular level.
The darkness part is apparently that as soon as your "time receptors" don't receive any (mostly blue) light any more, your body begins to secrete melatonin. The levels rise, and when they've risen enough, you get tired.
It can actually mess things up, although probably less in the Mediterranean than more extreme places further from the equator (where the differences are more pronounced). I think people in the arctic have to sort of induce artificial day/night for themselves when it's always bright/always dark.
> One explanation could be that it's technically not "the first sunlight that hits you" in the chronological sense, but in relation to your own circadian rhythm
That would also be the case for regular jetlag, right? But if the sunset does have a strong influence on you, that could be one of the reason why you have more trouble with DST than with jetlag.
I don't feel sunset influences me at all, I've always been most energetic and focused at night (similar to many night owls). I barely even notice DST (not that my sleep is very good anyway, I had a lot of problems with drifting sleep/waking time. I got it somewhat under control with time-release melatonin, and perhaps simply getting older).
Being energetic/focused at night doesn't mean sunset doesn't influence you. I'm the same way. It could just mean your rhythm means you get tired at sunset+4h instead of sunset+1h like an average person.
Could also be that it's something like the middle between sunrise (or really, first sun exposure) and sunset (or really, first darkness) averaged over a few days?
I'm not sure we know the exact mechanism or have enough granular data to say.
Great article! My husband is one of those extreme larks. He thrives on his "bakers schedule", starting work at 4 am, falling asleep around 7 pm. I have geeked on this circadian stuff for a long time, despite being extremely average/ordinary in sleep patterns. I thought I knew it all after reading Internal Time and other books- also "Good sleep, good learning, good life" https://super-memory.com/articles/sleep.htm but your description of Daylight Savings effects, and the changes in rhythm from youth to old age, are really helpful. (I now understand why I was so miserable for a while after returning home to US east coast from Asia, in college)
Ha, wow, 7pm sleep time is even crazier than the girl I knew :)
Internal Time is the best book I've found for the CRDs and CR in general. I've also stumbled upon the Supermemo articles on sleep and they've been very helpful.
What's interesting is that he seems to have DSPS/Non-24 but didn't know it; he just assumes everyone free-runs all the time without an alarm - but most people don't, unless they live in a cave. He also seems to believe all Non-24 is DSPS, at least last time I read anything of his on the topic (which is 5+ years ago). Whereas I am the other type.. but still, his understanding is much better than most :)
Great post! I live in NZ so nearly every international destination involves big time shifts. One question: I have a friend who doesn’t get jetlag. This is a useful trait for her as she travels a lot. As far as I know she sleeps fine at home too. How might this be explained?
This is relevant for smokers, those with covid or long covid, people with sleep apnea, people with other breathing conditions and people with circulatory problems.
I'd also note that oxygen levels are lower on planes and so this could be a factor in jetlag? But who knows if the effect might somtimes kick you *closer* to the timezone of your destination?!
Anyway, understanding the hypoxia link doesn't suggest a cure in most cases (except get a sleep apnaea pump) but it might help people with the conditions understand why their sleep sucks!
Interesting. Sleep apnea is luckily the one sleep thing I never had, even being morbidly obese. I think it only happens to back sleepers, and I'm mostly a side sleeper.
If there's enough of an effect from a plane ride, it would probably depend on the length and direction of your flight if that's helpful or harmful to adapting to your new timezone.
I've found that using light glasses, like the Luminette 3 they recommend, seem to help maintain entrainment when I'm already entrained to a daylight schedule. It's certainly cheaper and less bothersome than trying to replicate 20-100k lux sunlight for an entire room, with corn bulbs and stuff, like those Seasonal Affective Disorder treatment posts talk about. And certainly less boring/much less eye strain than those pathetic sun lamps that sit on your desk.
Though right now I'm just grateful that I can sleep free-running, and wake up and go to sleep in a relatively stable window, rather than waking up later every day, even if that window means going to sleep at 6 or 7 am. I guess I'll have to stay up later to get myself to daylight time again, and then use the sun/light glasses to keep pushing back my natural tendency to stay up late.
Haha I haven't finished reading it, cause it's hundreds of pages ;) People in the subreddit for Non24 seem to like it generally. I only found it years after fixing my Non24 with keto, so currently not in need heh. Lucky me!
I tried the 10k lux (?) lamp but got headaches way before I could get any sort of usable time in, usually within 5-10 minutes. And I usually rarely get headaches. Sunlight seems much better if possible.
Have you tried melatonin? Some people have success with that.
Some things I had found and made me think that limiting water/fluid consumption in the afternoon/evening could help circadian rhythms:
- vasopressin (the antidiuretic hormone) stimulates melatonin in some studies (on rats), and should be thus maximized before and during your sleep. Vasopressin could also be interesting wrt the functionning of the glymphatic system*);
- it seems like Intrinsically Disordered Proteins might play an important role in the mecanism of circadian rythms. The structure of these proteins might be influenced (their arrangement might be more structured) by osmotic stress/osmolytes and thus not drinking fluid might influence circadian rythms synchronization (though a big hypothesis).
Hm, I've personally experimented quite a bit with late fluid consumption and never noticed a difference. Basically, as long as I don't have to wake up at night to pee, there doesn't seem a difference at all.
Yea, could be for sure. Since I've been keto for nearly a decade, all my recent experiments (when I got serious enough to write stuff down etc) were on keto. Plus, off keto I would experience the Non-24 again, which is ALSO a huge confounder :)
I've definitely noticed pretty extreme differences in water retention even on "keto." My Standard American Keto (very high protein, high fiber) I was drinking a ton and peeing out a ton, and had lots of bloaty water weight.
On ex150, which is very low fiber and very low protein and therefore insulin, I drink way less, don't pee nearly as often, and I don't wake up in the middle of the night to pee.
1. Early life may have occurred deep in the oceans fuelled by the warmth of the Earth so the creatures were not really interested in the sun, probably only developed circadian rhythms later when they colonised the upper water layers (er, sorry, this was not really necessary, just had to say it out).
2. I've lately been a bit confused by this topic: the anthropologists have been claiming that hunter-gatherers are opportunistic sleepers, who sleep whenever they can and want and overall much less than us; infants have no circadian rhythms whatsoever and are only trained by parents to have these; many peoples have siestas at noon and therefore totally different sleep-wake patterns than once-per-day sleepers. Yet the sleep patterns of contemporary men in 'advanced' societies are highly heritable and hard to change. This is a contradiction, I can't solve it.
3. "SUN SUN SUN SUN SUN"
Sun? You mean the small shiny thing we see once a week through a frosty mist?
> Sun? You mean the small shiny thing we see once a week through a frosty mist?
You must be British? :D
I've seen various claims about sleep in hunter-gatherers, but the few studies I actually saw where they tested this, most of them slept pretty much exactly like us. They did not sleep all the time, they did not sleep way less, most did not regularly nap (although more in the summer!), they did not have "2 sleeps" with a long waking period in between. They pretty much slept like we do.
That said; a siesta can make sense, as can a "second sleep"/night activity time. I could imagine for example if it's too hot to comfortably sleep soon after sunset, you would go to bed later, and if it's too hot/bright out to keep sleeping enough too early, maybe you just get tired enough around noon?
And if it's dark for 16h a day in the winter, you can't possibly sleep that entire time. So unless you're a night owl or lark, it could spontaneously develop in a way where you sleep from say 9-12, stay up for a few hours, then sleep some more.
About the baby thing; I think their circadian rhythm is biologically set, it's not training by the parents. Just like our rhythm changes as we age, it's completely bonkers the first few months or years until it becomes what we'd consider "normal."
Seems true enough, though the emphasis placed on genetics is what we'd predict from first principles: "imagine an article on sleep written by someone very well informed but also suffering from one of the rarest and most debilitating genetic sleep variations". Most people are in the middle of the genetic bell curve, and their sleep problems are behavioral - hearing this information will provide them rationales for their unwillingness to change. For those on the tails, though, this could be life-saving.
Oh but three plugs (heh, pun intended) for technologies:
1) the point of having the room dark isn't for when your eyes are closed -- it's for when you open your eyes at night while still cognitively unconscious. That's why even small amounts of light are deleterious. Sleep masks come in a huge variety of fits and shapes, and you can just return them to amazon if they're not 100% comfortable.
2) Ear plugs have gotten way better, and again there are a ton of options. Can't return those, but they're cheap. My personal sense of the research on this one is that it's like they're trying to do a crossover trial on seatbelt efficacy: belts are usually worthless, but sometimes aren't. Similarly, earplugs can't protect your sleep against silence or against really loud noises, but can against some in the middle. Small sample sizes capture this poorly, but the effect is positive.
3) Artificial ights can be much brighter than the garbage they sell for circadian helps. And there are much bigger bulbs than most are. If you look up at the ceiling of a cathedral or other nicely-lit indoor space (not a fluorescent warehouse), the bulbs in the ceiling aren't the little ones you have at home. They're called "mogul" bases and they're big. Bulbs for these come in various colors (yellower if you want to simulate morning sun, bluer if you want to make the room feel more like midday). You can DIY a sun lamp for less than $50.
Tell her to try different ear plugs, there are very different shapes/foams types. I've had the hard/rough ones too that hurt after a few hours, but there are also very comfortable ones. I think Howard Leigh Lite is what I liked.
3) I didn't mention the sun lamps because I've personally only had bad experiences. I can barely do 5-10 minutes without getting headaches, and I'm not usually a headache person. I never get this when in the sun, so I recommend the sun instead.
2) Yea, ear plugs can help with (certain) noises. Hopefully your bedroom is quiet enough that you don't need earplugs regularly. I do travel with earplugs because hotels are often noisy (ice machine, elevators, ..)
1) Yea, fair point. I still think that a little bit of ambient light isn't that bad; sure, if the neighbor is pointing floodlights at you, get the curtains.
I also think I did address the behavior points; yea, normies can shift their 2h window from "slightly problematic" to "good" without much effort. I told you how :) Their general window is still genetically determined though.
For those who like words: Animals that are most active at dawn and dusk are crepuscular, which can be further divided into matutinal (dawn) and vespertine (dusk).
I looked that word up, but decided I was being made fun of, clearly crepuscular can't be a real word.
I had a feeling you already knew it! But, if you hadn't left it out, I wouldn't have learnt matutinal when I made double checked I had the right word, so thanks for that :)
Lol I didn't "know" it ;) I had to look up diurnal, too ;)
I don't understand how the darkness part of entrainment works. I'm in mediterranean, daytime duration ranges from roughly 16 hours in the summer to just under 9 hours in the winter. If that had major influence, it seems like it would just be messing the rhythm up.
But then, if it's only (or mostly) about morning sun exposure, daylight saving time would not be such a big deal (if you don't wake up at sunrise, which I guess most people don't?). The clock shifts, you wake up with an alarm clock an hour earlier, and then you immediately get sunlight exposure at waking time, just as you would if you traveled.
Maybe I'm out of touch and most people don't actually get up more than an hour after sunrise? But when the clock shifts forward in March, the sunrise is around 5:40 (shifting to 6:40 next day). If you get up at 7, you should be good.
I don't know if it's the combination of sunrise/sunset, but I naturally wake up significantly after sunrise (often 2-3h!) and DST still hits me quite hard. In fact, it seems to hit night owls much harder than morning larks.
One explanation could be that it's technically not "the first sunlight that hits you" in the chronological sense, but in relation to your own circadian rhythm. I.e. if I'm a nightowl and I wake up at 10am, using an alarm to wake up at 5am and getting into the sun wouldn't necessarily help. I would need the sunlight at 9-11am. Similar with sunset. Similar to wakeup, I get tired around 3-4h after sunset. But yea we don't exactly have a ton of data/understanding on how exactly it impacts people at that granular level.
The darkness part is apparently that as soon as your "time receptors" don't receive any (mostly blue) light any more, your body begins to secrete melatonin. The levels rise, and when they've risen enough, you get tired.
It can actually mess things up, although probably less in the Mediterranean than more extreme places further from the equator (where the differences are more pronounced). I think people in the arctic have to sort of induce artificial day/night for themselves when it's always bright/always dark.
> One explanation could be that it's technically not "the first sunlight that hits you" in the chronological sense, but in relation to your own circadian rhythm
That would also be the case for regular jetlag, right? But if the sunset does have a strong influence on you, that could be one of the reason why you have more trouble with DST than with jetlag.
I don't feel sunset influences me at all, I've always been most energetic and focused at night (similar to many night owls). I barely even notice DST (not that my sleep is very good anyway, I had a lot of problems with drifting sleep/waking time. I got it somewhat under control with time-release melatonin, and perhaps simply getting older).
Being energetic/focused at night doesn't mean sunset doesn't influence you. I'm the same way. It could just mean your rhythm means you get tired at sunset+4h instead of sunset+1h like an average person.
Could also be that it's something like the middle between sunrise (or really, first sun exposure) and sunset (or really, first darkness) averaged over a few days?
I'm not sure we know the exact mechanism or have enough granular data to say.
Great article! My husband is one of those extreme larks. He thrives on his "bakers schedule", starting work at 4 am, falling asleep around 7 pm. I have geeked on this circadian stuff for a long time, despite being extremely average/ordinary in sleep patterns. I thought I knew it all after reading Internal Time and other books- also "Good sleep, good learning, good life" https://super-memory.com/articles/sleep.htm but your description of Daylight Savings effects, and the changes in rhythm from youth to old age, are really helpful. (I now understand why I was so miserable for a while after returning home to US east coast from Asia, in college)
Ha, wow, 7pm sleep time is even crazier than the girl I knew :)
Internal Time is the best book I've found for the CRDs and CR in general. I've also stumbled upon the Supermemo articles on sleep and they've been very helpful.
What's interesting is that he seems to have DSPS/Non-24 but didn't know it; he just assumes everyone free-runs all the time without an alarm - but most people don't, unless they live in a cave. He also seems to believe all Non-24 is DSPS, at least last time I read anything of his on the topic (which is 5+ years ago). Whereas I am the other type.. but still, his understanding is much better than most :)
There's also 'Process S', and somehow melatonin seems to be tied up with leptin, not that I have the faintest idea how either of those things work.
You can get early about 1 hour per day or get later by 2 hours per day.
Yea, pretty much
Great post! I live in NZ so nearly every international destination involves big time shifts. One question: I have a friend who doesn’t get jetlag. This is a useful trait for her as she travels a lot. As far as I know she sleeps fine at home too. How might this be explained?
Hm, not sure exactly. She might have a relatively weak circadian rhythm? What's her sleep like, early bird, night owl, ..?
Night owl I think
Me too. Not sure why then, would be interesting to have her track it some time.
Coincidentally I was doing some research on circadian rhythms myself recently.
Circadian rhythms are affected by hypoxia, (shortage of oxygen).
This article describes it: https://pubmed.ncbi.nlm.nih.gov/38067152/
This is relevant for smokers, those with covid or long covid, people with sleep apnea, people with other breathing conditions and people with circulatory problems.
I'd also note that oxygen levels are lower on planes and so this could be a factor in jetlag? But who knows if the effect might somtimes kick you *closer* to the timezone of your destination?!
Anyway, understanding the hypoxia link doesn't suggest a cure in most cases (except get a sleep apnaea pump) but it might help people with the conditions understand why their sleep sucks!
Interesting. Sleep apnea is luckily the one sleep thing I never had, even being morbidly obese. I think it only happens to back sleepers, and I'm mostly a side sleeper.
If there's enough of an effect from a plane ride, it would probably depend on the length and direction of your flight if that's helpful or harmful to adapting to your new timezone.
What do you think of the VLiDACMel document? https://circadiaware.github.io/VLiDACMel-entrainment-therapy-non24/SleepNon24VLiDACMel.html It's like hundreds of pages about non-24 treatment and experimentation.
I've found that using light glasses, like the Luminette 3 they recommend, seem to help maintain entrainment when I'm already entrained to a daylight schedule. It's certainly cheaper and less bothersome than trying to replicate 20-100k lux sunlight for an entire room, with corn bulbs and stuff, like those Seasonal Affective Disorder treatment posts talk about. And certainly less boring/much less eye strain than those pathetic sun lamps that sit on your desk.
Though right now I'm just grateful that I can sleep free-running, and wake up and go to sleep in a relatively stable window, rather than waking up later every day, even if that window means going to sleep at 6 or 7 am. I guess I'll have to stay up later to get myself to daylight time again, and then use the sun/light glasses to keep pushing back my natural tendency to stay up late.
Haha I haven't finished reading it, cause it's hundreds of pages ;) People in the subreddit for Non24 seem to like it generally. I only found it years after fixing my Non24 with keto, so currently not in need heh. Lucky me!
I tried the 10k lux (?) lamp but got headaches way before I could get any sort of usable time in, usually within 5-10 minutes. And I usually rarely get headaches. Sunlight seems much better if possible.
Have you tried melatonin? Some people have success with that.
Some things I had found and made me think that limiting water/fluid consumption in the afternoon/evening could help circadian rhythms:
- vasopressin (the antidiuretic hormone) stimulates melatonin in some studies (on rats), and should be thus maximized before and during your sleep. Vasopressin could also be interesting wrt the functionning of the glymphatic system*);
- it seems like Intrinsically Disordered Proteins might play an important role in the mecanism of circadian rythms. The structure of these proteins might be influenced (their arrangement might be more structured) by osmotic stress/osmolytes and thus not drinking fluid might influence circadian rythms synchronization (though a big hypothesis).
Some resources regarding this last point:
- https://www.cell.com/molecular-cell/abstract/S1097-2765(23)00705-0
- https://biosignaling.biomedcentral.com/articles/10.1186/s12964-020-00658-y
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5363718/
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2937257/
*https://open.substack.com/pub/leadtheway/p/glymphatic-system
Hm, I've personally experimented quite a bit with late fluid consumption and never noticed a difference. Basically, as long as I don't have to wake up at night to pee, there doesn't seem a difference at all.
What I posted is obviously a theory, but keto diet might be a confounder here?
Yea, could be for sure. Since I've been keto for nearly a decade, all my recent experiments (when I got serious enough to write stuff down etc) were on keto. Plus, off keto I would experience the Non-24 again, which is ALSO a huge confounder :)
Keto as a confounder came to my mind because of its effect on insulin and thus water retention.
Anyways, that's cool you've found what works for you :)
I've definitely noticed pretty extreme differences in water retention even on "keto." My Standard American Keto (very high protein, high fiber) I was drinking a ton and peeing out a ton, and had lots of bloaty water weight.
On ex150, which is very low fiber and very low protein and therefore insulin, I drink way less, don't pee nearly as often, and I don't wake up in the middle of the night to pee.
Thank you! Some comments:
1. Early life may have occurred deep in the oceans fuelled by the warmth of the Earth so the creatures were not really interested in the sun, probably only developed circadian rhythms later when they colonised the upper water layers (er, sorry, this was not really necessary, just had to say it out).
2. I've lately been a bit confused by this topic: the anthropologists have been claiming that hunter-gatherers are opportunistic sleepers, who sleep whenever they can and want and overall much less than us; infants have no circadian rhythms whatsoever and are only trained by parents to have these; many peoples have siestas at noon and therefore totally different sleep-wake patterns than once-per-day sleepers. Yet the sleep patterns of contemporary men in 'advanced' societies are highly heritable and hard to change. This is a contradiction, I can't solve it.
3. "SUN SUN SUN SUN SUN"
Sun? You mean the small shiny thing we see once a week through a frosty mist?
> Sun? You mean the small shiny thing we see once a week through a frosty mist?
You must be British? :D
I've seen various claims about sleep in hunter-gatherers, but the few studies I actually saw where they tested this, most of them slept pretty much exactly like us. They did not sleep all the time, they did not sleep way less, most did not regularly nap (although more in the summer!), they did not have "2 sleeps" with a long waking period in between. They pretty much slept like we do.
That said; a siesta can make sense, as can a "second sleep"/night activity time. I could imagine for example if it's too hot to comfortably sleep soon after sunset, you would go to bed later, and if it's too hot/bright out to keep sleeping enough too early, maybe you just get tired enough around noon?
And if it's dark for 16h a day in the winter, you can't possibly sleep that entire time. So unless you're a night owl or lark, it could spontaneously develop in a way where you sleep from say 9-12, stay up for a few hours, then sleep some more.
About the baby thing; I think their circadian rhythm is biologically set, it's not training by the parents. Just like our rhythm changes as we age, it's completely bonkers the first few months or years until it becomes what we'd consider "normal."
Seems true enough, though the emphasis placed on genetics is what we'd predict from first principles: "imagine an article on sleep written by someone very well informed but also suffering from one of the rarest and most debilitating genetic sleep variations". Most people are in the middle of the genetic bell curve, and their sleep problems are behavioral - hearing this information will provide them rationales for their unwillingness to change. For those on the tails, though, this could be life-saving.
Oh but three plugs (heh, pun intended) for technologies:
1) the point of having the room dark isn't for when your eyes are closed -- it's for when you open your eyes at night while still cognitively unconscious. That's why even small amounts of light are deleterious. Sleep masks come in a huge variety of fits and shapes, and you can just return them to amazon if they're not 100% comfortable.
2) Ear plugs have gotten way better, and again there are a ton of options. Can't return those, but they're cheap. My personal sense of the research on this one is that it's like they're trying to do a crossover trial on seatbelt efficacy: belts are usually worthless, but sometimes aren't. Similarly, earplugs can't protect your sleep against silence or against really loud noises, but can against some in the middle. Small sample sizes capture this poorly, but the effect is positive.
3) Artificial ights can be much brighter than the garbage they sell for circadian helps. And there are much bigger bulbs than most are. If you look up at the ceiling of a cathedral or other nicely-lit indoor space (not a fluorescent warehouse), the bulbs in the ceiling aren't the little ones you have at home. They're called "mogul" bases and they're big. Bulbs for these come in various colors (yellower if you want to simulate morning sun, bluer if you want to make the room feel more like midday). You can DIY a sun lamp for less than $50.
I've suggested ear plugs to my mom, and she complains that they hurt to wear overnight. Same for ear muffs. I wish there was something for her.
Tell her to try different ear plugs, there are very different shapes/foams types. I've had the hard/rough ones too that hurt after a few hours, but there are also very comfortable ones. I think Howard Leigh Lite is what I liked.
Yeah they have ones that are like synthetic wax, too.
3) I didn't mention the sun lamps because I've personally only had bad experiences. I can barely do 5-10 minutes without getting headaches, and I'm not usually a headache person. I never get this when in the sun, so I recommend the sun instead.
2) Yea, ear plugs can help with (certain) noises. Hopefully your bedroom is quiet enough that you don't need earplugs regularly. I do travel with earplugs because hotels are often noisy (ice machine, elevators, ..)
1) Yea, fair point. I still think that a little bit of ambient light isn't that bad; sure, if the neighbor is pointing floodlights at you, get the curtains.
I also think I did address the behavior points; yea, normies can shift their 2h window from "slightly problematic" to "good" without much effort. I told you how :) Their general window is still genetically determined though.