Circadian Disruption Impairs Survival in the Wild

…just read that huge disasters, ranging from Exxon Valdez to Chernobyl, may have been due, in part, to ignorance of basic principles of circadian rhythms.  Gravitas.


circadian rhythms

The master circadian clock, or central oscillator, resides in a region of the brain known as the suprachiasmatic nucleus (SCN). Disrupting the SCN causes circadian arrhythmia and an inability to entrain to LIGHT but not FOOD (Marchant et al., 1997). Location of the peripheral oscillator is somewhat controversial, but may be in the dorsomedial hypothalamus (DMH). Global deletion of the clock gene Bmal1 causes circadian arrhythmia; restoration of this gene in the SCN restores the ability to entrain to LIGHT but not FOOD, and restoration in the DMH does the opposite (Fuller et al., 2008).  Optional background reading on circadian entrainment HERE.



On to the epic works of DeCoursey et al., which comprise some of the craziest experiments in circadian biology.

First, they induced circadian arrhythmia in cute little Antelope Ground Squirrels by disrupting the SCN (central pacemaker).  This is a relatively common technique in the field.


Antelope Ground Squirrel


then… they put ’em back into the wild to let Mother Nature take her course!  (THAT’s why I think it was crazy.)

This happened:



Significantly more animals with disrupted circadian clocks were predated!  this was partially behavioral-mediated; they’re usually diurnal (like humans), but arrhythmic animals left the safety of their underground burrows more frequently than LIGHT-entrainable control animals:



activity at food cache


This was confirmed in monitoring activity levels: intact (control) animals were active primarily during the days, whereas arrhythmic animals were active around-the-clock:



Importantly, there was no attempt to entrain these animals with MEAL timing, which is theoretically still functional in these animals… and this may have saved their lives.  Maybe predation was simply due to increased activity at night, maybe they weren’t able to outsmart predators… in any case, circadian arrhythmia = no bueno.



The researchers followed-up on this a few years later, in chipmunks (DeCoursey et al., 2000).  In this study, they used animals with SCN lesions (ie, circadian arrhythmia), control animals that received the surgery but no SCN lesion, and control animals that received no surgery (clever).  Here’s what they found:


cumulative survival


The top figure is cumulative survival during the first 15 days; the bottom figure is survival days 15-80. The take-home messages are: 1) getting your brain drilled into is pretty rough (top figure); and 2) circadian arrhythmia is significantly worse (bottom figure).

They also assessed nightly behaviors and found that even arrhythmic animals who didn’t leave their den at night were restless, which may have alerted predators to their location via sound, vibrations, or olfaction.

Another reason why predation was so bad in the first 15 days in arrhythmic animals, as speculated by the authors, was that “re-settlement” is an issue with this animal model.  Besides crappy sleep (restlessness) and increased nocturnal activity, some of the animals simply weren’t accepted back with their families :(

…social implications of circadian disruption?

An SCN lesion is clearly worse than conditions that induce circadian arrhythmia in humans.  LIGHT and FOOD are daytime phenomena.  In modern times, both are easily disrupted by technology, culture, lifestyles, habits, etc.  It’s easy to play on smart phones and watch TV, and convenient to skip breakfast while enjoying big dinners long after sunset… but these disrupt circadian rhythms.  Will it cause you to be predated?  Probably not by a wild animal, but rather by one of many modern diseases like diabetes or even cancer.

Bright light devices (in the morning) and blue blockers (at night) are band-aids that should be employed if you can’t avoid technology or change your lifestyle.  Meal timing is something that should be employed by everyone because it can entrain circadian clocks in a way that may have saved these poor animals, and it works independent from the central clock.



circadian rhythms



I found these studies quite compelling because they took place in the wild, with the hardest of hard endpoints.  Not activity monitors or food anticipatory behavior… SURVIVAL.  Animals with SCN lesions can survive quite long in captivity, where evolutionary survival adaptations are largely unnecessary.  But in the wild, robust circadian rhythms are vital.

And unlike some factors (like heredity), we have some control over the entrainment of our circadian clocks… not to be taken lightly.


And here’s a great video by a pioneer in circadian biology research, Dr. Joe Takahashi:


calories proper



Be Sociable, Share!
  • Kasha

    Excellent post, as always. I’ve often wondered if animals would have the upper or lower hand in the wild if they had a schedule like mine. Thanks for the post. :)

    • Bill Lagakos

      Thanks, Kasha!

      “I’ve often wondered if animals would have the upper or lower hand in the wild if they had a schedule like mine.”

      I think it depends on the specie’s evolutionary history (see Eg, some nocturnal animals have different adaptations than diurnal animals, like better senses of smell & hearing.

      Problems start when an animal’s light/dark activity schedule is flipped, and they haven’t had generations to adapt…

  • This Old Housewife

    Question, good doctor: what about nocturnal animals in the wild? Is this some sort of reverse circadian rhythm happening here? Granted, lives ARE shorter (as I’ve been studying in the neighbor’s feral cat colony next door), but extended from even the normal by regular feeding and contact/communication.

    My own vet tells me that if left entirely alone, cats will live about 2 years. If we intervene by adding a reliable food source, that lifespan can triple. If we add vaccines/worming, that lifespan can quadruple. If (by some miracle) we can add teeth cleaning, we’re looking at close to 20 years (and the feral animal will have become a full-fledged pet by then).

    All-outdoor cats like to sleep during the day (when it’s warmest outside), and hunt/socialize at night. Indoor cats adjust to our rhythms. My cats are indoor/outdoor, so they nap during the day, but they’re wide awake in the mornings (to see Hubby off to work at 5 a.m.) and in the evenings (usually lined up at the front window to watch the stray cat activity outside). They mimic the reverse circadian cycle as best they can.

    God only knows what goes on here during the night while we’re asleep–probably more window-watching of the strays outside, and seething of jealousy.

    • Bill Lagakos

      Wrt diurnal/nocturnal, it seems to work out well for many animals. For example, some prey species tend to sleep while their predators are hunting, and forage while their predators sleep (regardless of whether this is day or night).
      Some nocturnal animals have a better sense of smell & hearing, to account for reduced vision at night (some are even blind).
      So, it’s not ‘bad’ to be a nocturnal animal, because they’ve evolved in a way to optimally interact within their niche.
      I think.

    • Jack Kruse

      Stay tuned because my ubiquination series will talk about that………octopus is nocturnal and how they do it is special and reproduced in us in a very special way.

  • Thomas Hemming Larsen

    Hi Bill,

    I just got my Philips Hue light bulbs installed and I came to think of what would be best in the night. 1) Set the lights to follow f.lux at 2000K, 2) as I have the full colour spectrum to choose from I can make it completely red without any blue light. My question is really if I should aim for the lowest Kelvin or will red light in itself also the bad effects of the blue light? (I realise this might a silly question for a light scientist).

    • tanyewwei

      My opinion is that if you can control light to within the infrared wavelength band of 750nm to about 1080nm, then extra intensity isn’t a big factor.

      Of course the ideal would be LEDs, and I’m not familiar with the Philips Hue bulbs. When you say you can control them via f.lux, does the minimum Color Temp of the bulbs go as low as f.lux will go?

      If so, I personally think that you should get the Color Temp as low as possible. Under 1800K, and I think f.lux can get you down to 1400K

      • Bill Lagakos

        ^^^ thanks!
        agreed: my instinct is to keep color temp low at night.

      • Thomas Hemming Larsen

        Thanks. Hue light bulbs are LED. They can go down to around 2000K whereas I have f.lux to 1200K.

        I’ll just keep f.lux controlling them.

    • Bill Lagakos

      Not a silly question!

      For circadian experiments that need to take place in the ‘dark’ phase, the room is usually in red light for two reasons: 1) we need *some* light (to see); and 2) red light doesn’t disrupt circadian signaling like blue light does.

      Studies about temperature are mixed, but my gut says to keep it low (to hedge your bets)… based on my belief that short wavelengths of light at ANY temperature will induce phase delay (if exposed at night), whereas higher wavelengths need to be bright & long duration.

      • Thomas Hemming Larsen

        Thanks Bill. As I wrote to Shawn, I need to figure out how many Kelvin my lights are when I put them as red as possible. I don’t know if it can be calculated or you would have to measure it with a device.

    • Shawn Severinsen

      The HUE is really great. They are made up of three separate color coated LEDs, blue , green, and red. That means that when you set it to red, you are really getting red without any background blue light. I would recommend going as red as you can. If you go with a more orange color they may start adding blue and you basically want to do colors that use the red LED and perhaps a bit of the green LED while leaving the blue one off. Red or a reddish orange(for better color rendering) would be good.


      • Thomas Hemming Larsen

        Thanks Shawn. That was my thinking as well. The thing I still can’t figure out is if I put the lights as red as possible, how many Kelvin will that be at? I wan’t to keep Kelvin as low as possible too.

        • Bill Lagakos

          This website might help:

          Kelvins: red is lower than blue.
          You could also dim them.

          • Thomas Hemming Larsen

            Like I haven’t already signed up 😛

            Got it. They’re already dimmed via f.lux.

            What I meant is that I’m not sure if the Kelvin will be at the minimum if I turn them red. I’m working on some HTTP programming to control them more accurately both in terms of colour and temperature. If it all works out I should be able to set them very red with the minimum Kelvin – double whammy! :)

          • Shawn Severinsen

            Hey Thomas, I think your putting too much emphasis on the Kelvin scale my friend.

            That scale is simply an approximation of the color of radiation from a theoretical “black body” at a given temperature (in Kelvins). For lighting purposes, it is useful because an incandescent filament is close enough to a “black body”. The heat output (wattage) of the filament determines the color of the light. That’s why dimming an incandescent not only reduces the lumen output but shifts the color to the red due to reduced temperature. Now with LEDs and CFLs the color of light has nothing to do with temperature and is created by the coating it is manufactured with. Dimming an LED or CFL only lowers the lumen output and does not change the color of the light.

            The kelvin scale is only useful up to a point. Typically used rages are from 1800K to 25000K although for standard lighting applications the range is about 2000K to 6500K.

            If you use an orange lamp in the evening there really isn’t a Kelvin equivalent. Likewise if you set your HUE to pure red or orange output, the Kelvin scale dose not apply.


            The HUE has a function for programming based on the Kelvin scale (“ct”). If you use this function you will always have some blue light in the mix.

            Use the “xy” function and go for red or orange instead. Break free from the Kelvins! Lol. See the link below:


          • Thomas Hemming Larsen

            Thanks Shawn. Those were exactly the things I was wondering about.
            I’ve started looking into programming my lights like you mention (I just needed to know what to aim for :) )

          • Thomas Hemming Larsen

            I’ve now set them to 0.6750,0.322 which should be complete red. Btw, the xy function overrules colour temperature.

      • TechnoTriticale

        Re: The HUE is really great. They are made up of three separate color coated LEDs, blue , green, and red.

        In the teardowns I’ve been able to find, some Hues are clearly using discrete R-G-B LEDs, and with others it’s not so clear. In general, LEDs can trivially do Red and Green natively, and don’t need phosphors or coatings. Blue has always been the tricky color, and might be done by heterodyning, but is more likely being done with phosphor.

        Kelvin, color temp, CRI, “warm” and “soft” are not reliable metrics for low blue at the crucial wavelengths. You really need to see an SPD (spectral power distribution) plot for the bulb (and for the Hue, you’d need multiple). Due to the complexity of human color vision, principally color metamerism, you can’t trust your own lyin’ eye on this.

        Of the white light LED bulbs on the market, the only ones for which I’ve so far seen an SPD with acceptably low blue are the Cree “soft” whites. They are also dimmable. The SPD was reported independently. Cree publishes SPDs for their chips, but not, so far, their bulbs.

        That said, I’d be pretty confident that when you dial down the blue on a Philips Hue, you really are dialing down the blue.

        The Hue bulbs are expensive, but I would already be converting to them but for another potential issue with “smart” bulbs generally: using them increases the number of active RF transceivers in the home. We might be Krusing into trouble on that; replacing one hazard with another. So for the moment, blue blockers and Cree soft whites suffice.

  • tanyewwei

    Always love the posts!

    In this case, I assume that SCN lesions basically prevent any direct inputs to the SCN. So it’s not that the SCN can’t function, but just doesn’t have any information to work with, and can’t signal appropriately.

    I still that that all the conclusions made in the post are valid, since the fundamental problem is that the SCN can’t talk to the peripheral tissues in a coherent way.

    On a practical level, I ask myself:

    (a) What is the quickest way to screw up SCN inputs

    (b) What are potential measures for said SCN input

    There was a whole discussion on the Kruse forums regarding Cryptochrome and Melanopsin signalling, which I took part eagerly in 😛 —

    Everything starting from the post by Christos is pretty relevant here —


    Anyway, I like this paper ‘Expression of the Blue-Light Receptor Cryptochrome in the Human Retina’ —


    > Mice of the rd/rd;Cry1–/–; Cry2–/– genotype, which have no classical opsins or cryptochromes but retain melanopsin, exhibit nearly 3000-fold reduction in circadian photosensitivity
    > At face value, the retinal depletion data show that cryptochrome can mediate circadian photoreception in the eye in the absence of functional opsins. However, this conclusion is at odds with the finding that elimination of opsins by genetic ablation abolishes all visual and non-visual photoresponses.
    > Clearly, in the absence of opsins, cryptochrome cannot generate an action potential for neurotransmission from the retina to the SCN?


    Jack also posted something about cryptochromes and magnetic signalling —



    – Cryptochrome and Melanopsin activity is probably the best measure for SCN input

    – Cryptochromes can pick up magnetic signals

    – Cryptochomes signal light input to the SCN

    – Melanopsin can signal light input to the eye, gravitational changes, magnetic field changes, and has a bunch of G-protein coupled receptors to talk to other proteins, including the integrins that link the entire collagen network of the body.

    This compound can basically sense everything and relay that information to the SCN, as well as potentially the rest of the body.

    – Screw with human Melanopsin, and everything else down the chain is screwed up too … excessive blue light is the best way to do this


    I also think that your aversion toward artificial blue light in the morning before sunrise is logically sound.

    The cryptochromes and melanopsin on the retina can pay attention to gravitational and magnetic changes as the earth rotates (both are higher at night).

    Feeding the retina with just blue light input is sorta-a-mismatch-but-not-quite, only because blue light is such a strong signalling factor, but then again, I don’t know just how much the other factors come into play.

    But again, we’re dealing with side effects that are unknown, and obviously just having extra blue light input doesn’t accurately simulate an actual sunrise caused by the earth’s rotation.


    • Bill Lagakos

      Thanks! I appreciate your feedback, as always.

      “I assume that SCN lesions basically prevent any direct inputs to the SCN”

      yes, the SCN is literally fried in this model: no inputs or outputs.

      “just having extra blue light input doesn’t accurately simulate an actual sunrise caused by the earth’s rotation”

      agreed, but blue light at our subjective ‘night’ and blue blockers during our subjective ‘morning’ works quite well for shift workers! They’re still out of phase, but simply correcting the timing of light exposure is therapeutic in this population.

      • tanyewwei

        Ha, the SCN lesion thing is more just an academic curiosity for now TBH :)

        I was actually thinking about some of the stuff that Jack Kruse has been saying about the SCN not having a lot of efferents.

        Instead, he claims that SCN output is largely based on oscillations, so I was wondering how output would be affected. Sounds like the surrounding collagen matrix is sufficiently destroyed by that point to transmit these oscillations anyway ….


        The blue blockers at night can definitely work very well to keep melatonin levels unaffected.

        Then, blue light in the morning definitely works very well to wake the person up and get wakeful processes firing pretty well.

        I’ll add one point regarding most bright light devices people use in the morning though ….

        A lot of the cheaper sunrise simulators or bright light therapy devices out there are mostly just blue light emitting devices.

        My personal concern with blue-light-only bright lights in the morning before sunrise, is that you can stimulate extra activity despite high cortisol levels (and hence looser collagen in the entire body)

        I think it’s more useful to have a device that has either concurrent red-light emission to re-zip collagen, or supports the full visible spectrum of sunlight.

        Example: a device like this one, which is basically a timed set of LEDs spanning the entire visible spectrum —

        Oh, and hot showers when you wake up is always nice, and could possibly help to re-zip collagen, and lead to overall work readiness as a whole.

        Make it a hot-then-cold contrast shower to get the benefits of heat plus cold to really get the nervous system up and firing.

        • Kasha

          All excellent in theory, but hot and cold showers do not “wake up” my nervous system and make it work right. Neither does just blue blockers. People who actually have these problems with their SCN are not necessarily fixable. It requires trying to get the best out of the situation and controlling light, dark, and known zeitgebers to try to manually entrain yourself day in and day out. It requires a boring life, no stress- good or bad, no deep emotions, no temperature change, no change… everything remains constant. As impossible as that is, that’s what we have to try to maintain or our bodies go haywire.

          • tanyewwei

            Hey, “no stress” can be fun! :)

            My version of no stress is long walks and reading books on the beach (I live in Cairns, Australia).

            I’m currently in Brisbane visiting a friend, and playing with his kids (two boys, 5 and 9), while barefoot and rolling around in the wet and rainy backyard was pretty awesome!

            When I made the move from Melbourne to Cairns last September, I recovered from almost everything I suffered from within 2 weeks

            The biggest source of stress for me in Melbourne was just some unknown factor ….

            I tried a lot of stuff, but you can’t add energy to a depleted body and hope that it can actually use that energy in the context of a shitty stressful environment.

            I talk a little about the environment in Melbourne vs Cairns here —

            I like where I am much better: consistent sunshine through the year, consistent temp ranges, whenever you’re emotionally stressed you step on the beach, etc ….

            So yeah, I do agree with you that sick people should get consistent light cycles, avoidance of circadian-disrupting nn-EMF, and get some time to relax.


            When I was sicker (in Melbourne), I found contrast showers as a great way to recover from certain issues. Example: I’d drink coffee, not be able to deal with the xanthines, and get literally close to a panic attack.

            The hot-then-cold shower then works by utilising the fournier effect that Dr Jack Kruse has been touting.

            My brother on the other hand, found them to do absolutely nothing for his migraines. :

            I think they help if you have peripheral collagen issues that worsen neuro-musculor crosstalk.

            The particular definition of “wake up the nervous system” here means to tighten up collagen in peripheral tissues, and allow them to communicate better with each other and the CNS, and therefore be more prepared for doing whatever sort of work demands are placed on the body.

            For brain-specific issues, my brother has found that ice packs right over the carotids help a lot more with migraines — reduction in pain RPE, and reduction in time to recovery (say 1 hour vs the usual 8 hours of nonsense).

            A plausible theory is that it helps to cool a significant enough chunk of blood that gets to the brain, and improves whatever malfunctioning collagen in the brain that leads to the unwanted water shifts.

            (Sidenote: in his case, it’s definitely neuro-overexcitation that leads to water balance shifts in the brain, that forces osmotic pressure up in certain areas that cause the pain)


          • Kasha

            I don’t doubt that hot/cold showers work for normal people. That I don’t know… my body’s temperature control doesn’t work properly. Anything above 74 degrees F and I feel like I’m dying. If it were 50 degrees year round I’d be A-ok. Below 0 is fine too as I’m from Wisconsin (which is colder than Alaska right now). I like Brisbane. One of my good friends lives there. Such a wonderful variety of well, everything there.

            That’s good that it took you 2 weeks to recover from the move. For me, I would be fine the first few days and could keep up with everyone, then I’d start sleeping, would need strong antibiotics about 10 days after the move for some kind of rampant infection, and would only start recovering after 6 weeks. It’s been like that all my life. Now it’s just more pronounced and I don’t recover the energy I should have at my age.

          • Jack Kruse

            because the pineal is vascular and CT will help a broken SCN (due to low DHA) better than just a move. There is another reason too……Archimedes principle. Stay tuned.

          • rs711

            “It requires a boring life, no stress- good or bad, no deep emotions, no temperature change, no change… everything remains constant”

            I don’t think that’s quite correct when keeping the concept of anti-fragility in mind. Health &/or circadian entrainment requires variation, to some degree or other, akin to a margin of heterogeneity. The last thing you want is ‘flat’ homogeneity because that is not the world we live in. Variation in temperature, light and foods are both things we need to adapt to and also cannot do without. The response-adaptation feedback look, like science, is a self-correcting processes. Both internal and external cues are in constant feedback where if our responses were to be plotted, they’d look like sine waves rather than a flat-line.

          • Kasha

            It depends on what’s wrong. For the majority, yeah, you’re right… you want to have endogenous and exogenous entrainment. But I no longer respond to light/dark and melatonin and geophysical factors, stress, LIFE’S variations… things that I can’t control drastically affect my sleep/wake patterns for some reason. I’m not giving up, we’re trying to manage it based on what we’ve tried already. My case is complicated- it’s not going to self-correct. Pineal problems can be worked around, SCN problems are a bit different.

            There’s this misconception out there that everyone’s rhythms are going to do be on a 24.6 hr day if they just add light and zeitgebers at the right time. Sorry, CLOCK, PER, CRY, BMAL, REVERB genes can mutate. You can have lesions in your SCN, the SCN can hemorrhage, the cause of Sighted Non-24 isn’t known yet because no one studies it. Unlike the mice humans can’t get SCN transplants.

            There aren’t many but people like me do exist. Some chalk it up to neurodiversity, some see it as a disability because they can’t function in everyday life.

          • rs711

            I’m sorry to hear you have such a condition :s

            Have you tried contacting Dan Pardi directly? He’s genuinely geeked out on all this stuff (+ it’s his carreer hehe!). If you’re that ‘fringe’ case, you might get his attention…

            You mentioned mutations in circadian genes/proteins – are you saying that it’s a possibility in your case or that it actually is so? Either way, a 23&Me work-up (raw data) will confirm that for you.

            Neurodiversity is often used to make “I don’t” sound smarter, so yeah, maybe…

            All in all, the slightly heterogeneous rhythmicity is still what your (or anyones) biology needs for proper function. So whether that’s achieved pharmacologically or otherwise I’m unfit to say. My guess is that if you’re unresponsive to such internal/external cues, that doesn’t mean they won’t help, simply that in & of themselves they’re insufficient – hence, as you say, need to look further, deeper.

            Good luck!

      • Jack Kruse

        there is still an input……..blood plasma. Pineal has few connections but massive blood flow and no BBB. Trust me as a brain surgeon operating on pineal tumors is a nightmare day because of the vascularity.

  • Gerard Pinzone

    I wonder how arctic and antarctic wildlife adapt when transplanted to the temperate zones. Are polar bears and penguins at the San Diego Zoo affected by the change in sunlight swings as well as the warmer temperatures?

    Bonus: animated gif.

    • Bill Lagakos

      “I wonder how arctic and antarctic wildlife adapt when transplanted to the temperate zones. ”

      100% no bueno. Imho, it’s one of the reasons why birth rates are poor in these animals.

    • Jane Plain (Woo)

      lotta manic patients there i bet

  • Jack Kruse

    I was waiting for you to go there, Bill. Now, here is the physics behind why it happens.

  • Michael

    Just a question: What time would you feed a dog?
    Also, tinkering with light at night (and possibly food) might predispose one to biphasic sleep. If one were to consider 8 hours of solid sleep to be the most practical today, then doing so might no longer be “optimal”, at least to all practical intends and purposes. I’ve noticed myself that not using light at night does indeed cause (?) me to wake up during the night. That’s okay for me, but not everyone has enough spare time to live like this. I was pondering this yesterday as I read A Roger Ekirch’s “At Day’s Close” where he touches on this subject in the final part, especially chapter 12, “Sleep We Have Lost”. A interesting read, perhaps not worth buying, but check the library.

    • Michael

      By biphasic I meant a 1st and 2nd sleep separated by an hour or more in the middle. Not sure if I’m using correct terminology.

    • Bill Lagakos

      I’d feed a dog in the morning or morning + afternoon. They’re somewhat better off than us, because not bombarded with blue light devices at night, etc.

      I’ve read about biphasic sleep, and, well, am not entirely convinced… interesting, though.

  • Bill Lagakos

    Awesome video on LIGHT and HEALTH ?

  • Pingback: Weekend Link Love – Edition 337 | Lose Fat By Walking()

  • Pingback: Weekend Link Love – Edition 337 |