Regulating Circadian Rhythm (and why that’s important)

February 27, 2014 in Categories: , by

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I can’t take credit for this analogy,  but I absolutely love it:  hormones are like a symphony and circadian rhythms are the conductor.

The term circadian rhythm refers to the fact that a huge array of biological processes within the human body (and indeed all forms of life on Earth) cycle according to a 24-hour clock.  Circadian rhythm allows your body to assign functions based on the time of day (and whether or not you are asleep); for example, prioritizing tissue repair while you are sleeping, and prioritizing the search for food, metabolism, and movement while you are awake.  Circadian rhythms are how your body knows what time it is (like when it’s time to get up in the morning)–and properly regulated circadian rhythms are critical for health.

Your brain has a master clock, called the circadian clock, which is controlled by specialized cells in a region of the brain called the suprachiasmatic nucleus of the hypothalamus (typically abbreviated SCN–and how’s that for some awesome trivia!).  This is the conductor.  The circadian clock then controls the ebb and flow of certain hormones (cortisol and melatonin being especially important) which act as signals of the circadian clock throughout the body.

Melatonin and Cortisol

As the levels of cortisol and melatonin cycle throughout the day (cortisol peaking shortly after waking and melatonin peaking during the middle of the night), they tell all the cells in your body what “time” it is.  The cells each then  then set their own internal clocks to the brain’s clock (like setting your watch to Greenwich Mean Time).

The circadian clock is set by a variety of external factors, but most importantly light during the day and dark at night (also called the light-dark cycle).  In order to have healthy circadian rhythms, your circadian clock needs to be set to the right time.

The vast majority of your hormones cycle during the day (not just melatonin and cortisol).  Not only that, but sensitivity of different types of cells to different hormones can also cycle.  This impacts every system in your body, from your immune system, to how well you digest your food, to how much insulin is released in response to sugar intake–all change based on the time of day.  This is the symphony.  And, this is why prioritizing circadian rhythms is so important:  it not only helps regulate the levels of and sensitivity to different hormones, but even more importantly, it regulates the natural ups and downs that your hormones go through throughout the day and night.  And this is necessary for health.  When your circadian rhythms are properly regulated, you sleep well, you have energy in the mornings, your energy is constant throughout the day until it starts to gradually diminish in the evening… and it reduces your risk of chronic disease!  Yes, ALL chronic disease!

What can you do to set your circadian clock, protect your circadian rhythms and therefore regulate so many important hormones? 

1. Get Bright (Blue) Light Exposure During The Day:

The light-dark cycle mentioned above is the most important signal to your circadian clock.  This means that one of the best ways to set your circadian clock is be exposed to bright (ideally sunlight) during the day, but be in the dark at night.  In fact, sunlight exposure during the day is probably the single most important thing you can so to support the normal production of melatonin in the evening.

The component of sunlight that tells your circadian clock that it’s daytime now is blue light.  You have photoreceptors in your eyes and your skin that are sensitive to blue light (the receptors in your eyes are much more sensitive than in your skin) which then convey the signal to the brain.  How much time outside is enough?  If it’s a sunny day, as little as 15 minutes (without sunglasses!).  If it’s cloudy, 30 minutes to an hour is better.  And of course, the more the better.

So, what do you do if you’re a shift worker or live in a climate or have other barriers to being outside?  There’s a great biohack available for getting this blue/sun light exposure during the day: a light therapy box.  There doesn’t seem to be a difference between the white light boxes and the blue light boxes in terms of supporting melatonin production, so you can pick the least expensive option–but choose one that is bright, at least 10000 lux.  Use it for at least 15 minutes at roughly the same time every morning or mid-day.  Another option is to make many small changes to brighten your environment during the day:  use sunlight spectrum light bulbs in your house (but you’ll want to avoid using these light bulbs in the evening), keep curtains open during the day, make sure your computer monitor and other screens are set to its brightest setting, drive with the windows down… All of these things help, but still aren’t typically as bright as a light therapy box or just being outside, even on a cloudy day.

2. Avoid Bright (and Blue) Light in The Evening

Just as it’s important for your body to get the signal that it’s daytime during the day (or your day, if you’re a shift worker and using a light therapy box), it’s important to tell your body it’s nighttime once the sun goes down.  This means avoiding blue light and sticking with red and yellow wavelengths of light as well as keeping the overall light level much dimmer.

You can achieve this important “darkness signal” to your circadian clock by keeping your indoor lighting as dim as possible in the evenings with dimmer switches, or just plain ol’ turning on fewer lights, in conjunction with  investing  in red or yellow lightbulbs for whatever lamps will be used in the evening.  If you plan to use a computer monitor or watch TV, there are two options.  The first is to install f.lux on your computer (it’s trickier to install on phones and tablets) and now set the screen brightness to the lowest setting.  The second, and probably the best biohack for supporting evening melatonin production (more technically called dim-light melatonin production) is to wear amber-tinted glasses for the last 2-3 hours of your day.  In fact, several scientific studies show that wearing amber-tinted glasses in the evening improves sleep quality and supports melatonin production.  What are amber tinted glasses?  Quite simple: glasses with yellow lenses.  These could be driving glasses, glaucoma glasses, or safety glasses (my personal preference in for the large lens of safety glasses because they also block peripheral light and there are options that can fit well over regular glasses… plus they’re super cheap!).    Amber-tinted glasses are also a great option for shift-workers.

A more sophisticated option for getting both your bright blue light in the day and your dim red light in the evening is programmable light bulbs where you can set the color spectrum and the brightness for the time of day (and you can program them to automatically change at whatever time you want! how cool is that!).  It’s an investment, but then you can ditch the goofy safety glasses (although, you’ll want to pull them out again if you’re going to watch TV).

3. Reduce and Manage Stress

You probably recognize cortisol as being the master stress hormone.  It’s also a very important circadian rhythm hormone.  This means that if you’re under stress, not only do you have all the effects of elevated and dysregulated cortisol to deal with, but you also disrupt your circadian rhythms.

Reducing stress means to remove stressors from your life.  Whether that’s saying “no”, asking for help, or making changes to the structure of your life, whatever you can do to reduce stress will make a difference.  Oh, and coffee increases your body’s stress response to psychological stressors, so you might want to reduce coffee or give it up altogether.

Managing stress means increasing activities that help regulate cortisol and make you more resilient to stressors.  This might include taking up meditation, yoga, going for a walk at lunch, taking a bath, or just making time for a good laugh or a hobby in your life.

4. Go To Bed On Time! (and get enough sleep!)

Just like being stressed can affect circadian rhythms, so can ignoring them.  Your melatonin starts increasing about two hours before bed to prepare your body for sleep.  If you’re muscling through that with a sugary snack, a scary movie, or whatever else you do to keep yourself awake at night, you are affecting your circadian rhythms.

Aim for 7-10 hours of sleep every night (and most people will need between 8 and 9).  This means shifting your bedtime earlier so you aren’t muscling through that fatigue to get a second wind (which by the way, usually also means you’re increasing your cortisol right when it’s supposed to be at its lowest). For more on sleep and the immune system, see this post.

5. Sleep in a Cool Completely Dark Room (and keep your indoor temperature warmer during the day).

Sleeping in a completely dark room is really important for protecting circadian rhythms.  Cover up any LED lights on phones, toothbrushes, baby monitors, or whatever other gadgets you have plugged in in your room (masking tape works great for alarm clocks and duct tape works great for little LED lights).  And ditch the nightlights or switch to ones with red light bulbs.  Blackout curtains can be one of the greatest biohacks for getting a good night sleep as can white noise generators (especially if there are high frequency/pitch noises in or outside of your home since these are very stimulating for the brain).

While you’re at it, ditch the alarm clock.  Waking up to a jarring noise is very stressful.  If you don’t have the luxury of sleeping until your body naturally wants to wake every morning (which is the best option for protecting your circadian rhythms and overall health), a light alarm is a great investment.

The temperature that you’re sleeping in is also a cue to your circadian clock.  Ideally your indoor temperature at night should be 65F or lower.  And actually, the converse is true:  being warmer during the day supports circadian rhythms, typically above 75F.

6. Get Activity

Getting some kind of activity during the day has been shown in clinical trials to support melatonin production.  There are a few exceptions though.  For example, intense activity later in the day can delay your melatonin production (basically keep you revved up longer in the evening) unless it’s routine (say, you always go to CrossFit in the evening and your body has adjusted).   And working out in a really bright environment in the evening can be a problem (the combination of bright lights, maybe in your gym, and activity in the evening suppresses melatonin).  But, other than that, any kind of activity any time of day (even better if it’s outside!) will help support circadian rhythms.

7. Keep your Blood Sugar Levels Well Managed

Many hormones are sensitive to swings in blood sugar, including both melatonin and cortisol.  This doesn’t mean eating low-carb (actually too low carb can disrupt circadian rhythms by increasing cortisol and affecting insulin sensitivity, plus high starch meals about 5 hours before bedtime have been shown to improve sleep quality), but rather to avoid spikes in blood sugar from high glycemic load foods.  If you’re following a Paleo diet, chances are really good you’re doing this already.

8. Be Social During The Day and Intimate At Night

This is something I learned from Dr. Paul Jaminet.  Social connection can influence your circadian clock.  Dr. Jaminet recommends limiting big social gatherings (and even things like watching TV shows that have lots of characters) to the daytime, and keep things intimate (just your family and closest loved-ones) in the evening.

9. Eat Organ Meat and Seafood

Melatonin is made from serotonin which is made from tryptophan.  Organ meat and seafood have more tryptophan while also having less of the other amino acids which compete with tryptophan to cross the blood-brain barrier.  So, eating more organ meat and seafood is a great way to boost production both of serotonin and melatonin.

Eating seafood also contributes long-chain omega-3 fats to your diet (DHA and EPA).  These help support circadian rhythms by improving neural health in the brain and by improving resilience to stressors (if you’re getting high dietary omega-3s, you secrete less cortisol in response to stress).

10. Embrace Seasonal Variation

It is natural, normal and healthy to sleep more in the winter and less in the summer.  But indoor lighting has robbed us of the natural seasonal variations in the amount of sleep we get, our activity levels, even our appetites.  Most of us live as though it’s summer year-round.  But, you can embrace seasonal variation using all of the biohacks mentioned in this post by adjusting things like bedtime (what time you dim the lights and put on your amber-tinted glasses) by the time of year.  Maybe aim for 9 or 10 hours of sleep in the winter, but only 7 or 8 in the summer.  Adjust your indoor temperatures to more accurately reflect what’s happening outside (this is also a great way to save on heating and cooling bills).  Eat seasonally (which means your carbohydrate intake will likely vary by season too, which will influence cortisol and melatonin through effects on insulin).  All of these things will help regulate your hormones in a healthy way… and you will feel the difference!

Want more details? Check out Chapters 4 and 7 in The Paleo Approach.


We’ve also learned that doing what we call “candle time” is a great way to wind down before bed.

No bright lights or electronic screens half an hour before bed.
Light a few candles. Read a real book by candle light (if possible).

Really relaxing and helps with the sleep!

Any suggestions on dealing with the upcoming time change? I dread having to adjust my body to it because I feel so “off” for several weeks.

Sarah, do you think it matters when you got those 8-10 hours of sleep? For example, I’ve read that it’s idea for everyone to sleep from 10:30-6:30, that we all have the same biological clock. But then Mark Sisson said the brains of night owls and morning people are different. So, it makes me wonder if consistency is more important than actual bedtime. I’m not talking about staying up all night. I’m just curious about the benefits of a bedtime of 10:30 vs. 9:00 or Midnight.

Consistency is absolutely more important. The most important thing is to get your circadian rhythm regulated — and that may mean different sleep/wake times for different people or even change your sleep/wake times. — Christina, Sarah’s assistant

I don’t doubt this at all! I still think it might be somewhat important to consider the natural light cycles – go to bed when it gets dark outside, wake up when the sun rises… but there’s certainly a lot of room for tweaking depending on your particular context or personality type.

Great post. This is so important, and I learned a few new things :) I think I know where you got your quote — it’s a great one for hormones! New to your blog. Very science base, which is good for the science geek in me.
Finally trying to go paleo all-the-way, however, more veggies, and minimal meat – me and red meat don’t get along :)

I look forward to reading more!

I used to occasionally take melatonin at night to help me sleep, but read that this should be avoided with autoimmune disease. Is there any truth to this? I can’t remember the exact reason, but think it had something to do with stimulation of the immune system. It was certainly a better option than any pharmaceutical sleep aid, but I’ve avoided it since…

Sarah discusses taking melatonin on page 258 of The Paleo Approach. The summary is that a smaller dose (.25 milligrams, not slow release) can be used for a short period of time, but that using it should only be considered after you’ve implemented the other diet and lifestyle changes outlined in the book (including spending time outside during the day, wearing amber tinted glasses, sleeping in dark room, and eating glycine and tryptophan-rich foods). — Tamar, Sarah’s assistant

Good article Sarah. I’m happy that since I’ve had Dr. Hansler (the guy from Low Blue Light Institute) on my podcast that more people are paying attention to this huge issue.

I read from another source (not Ray Peat) that a lot of people’s problem with depression might actually stem from *too much* serotonin rather than insufficient. And then from Dr. Diana Schwarzbein I saw a recommendation to eat more carbohydrate because it makes more serotonin which “helps” with depression. So I think there’s something to the idea that high-junk-carb eaters ARE making too much serotonin and that’s why they have the depression issues. It makes sense if you think about it. Dopamine is sort of the opposite of serotonin, and someone with too much dopamine has issues with impulsivity and even manic behavior, just the opposite of what you expect to see in a depressed person. If a person wants to “perk up”, the last thing they should do is try to make more serotonin.

There’s also the point that so many of us are sleep-deprived and of course, you make melatonin from serotonin (which in turn comes from tryptophan through a series of steps), so if you’re not sleeping, or the room doesn’t stay dark enough, you’ve destroyed your ability to make sufficient melatonin and bingo, you’ve got too much serotonin yet again.

(I think SSRIs probably work through their action on neurogenesis in the hippocampus, at least in most depressed people, which is why they take several days to work in most depressed people when they ought to be working almost instantly. No one actually *tests* a depressed person to see how much serotonin is in their brain; such a test would be impractical and dangerous. They’re guessing. On the basis of guesswork, we are put on these drugs which, it transpires, are much more dangerous than previously admitted. So before you go running for a pill to cure your ill, people, fix your diet and your sleep problems!)

Nice point about healthy sleep using up serotonin.

I’ve long since cleaned up my diet, corrected sleep, chelated mercury (read Andrew Cutler’s “Amalgam Illness” and the much easier to read “Fight Autism and Win”), and pretty much everything else… and while it’s too soon to say with certainty adding pregnenolone appears to have been necessary. I’m supplementing vitamin D3 too. Most people shouldn’t need to supplement pregnenolone and you’ll mess yourself up if you don’t need it but I simply don’t produce enough to feed my oversize Asperger’s brain. To be clear: fix diet and sleep first, then decide if anything else is necessary.

The idea that very low carb messes up sleep must be like the idea that very low carb slows down the thyroid. Maybe these are true for some people, but they are not true for everybody because I and other people have had opposite experiences.

It all comes down to finding out what works *for yourself*. There are some things that are going to be true for pretty much everybody, like we all need the same laundry list of vitamins and minerals and essential fats, but as far as proportions needed or what other foods and behaviors we need, that’s going to be a little different from person to person. It could be that the VLC person who sees their sleep disturbed might actually have a very different thing going on with them that has the cross-effect of making VLC mess up their sleep. You never know.

I sleep better with less carbohydrate, especially if I also quit caffeine.

By the way, leafy greens are carbohydrates too. I think people forget that.

The circadian clock then controls the ebb and flow of certain hormones […] which act as signals of the circadian clock throughout the body.”

The body has circadian clocks throughout the body, the SCN synchronises them through various hormonal signals. Cells in a petri dish maintain an almost precise 24h rhythm on their own.

Ko, Caroline H., and Joseph S. Takahashi. “Molecular components of the mammalian circadian clock.” Human Molecular Genetics 15.suppl 2 (2006): R271-R277.

Sancar, Gencer, and Michael Brunner. “Circadian clocks and energy metabolism.” Cellular and Molecular Life Sciences (2014): 1-14.

Archer, Simon N., et al. “Mistimed sleep disrupts circadian regulation of the human transcriptome.” Proceedings of the National Academy of Sciences (2014): 201316335.

this is all well and good information but when you’re older and going through so much in life that you hadn’t gone through before you worry, such as me going through chemo and getting sick each time that you dread when it comes time to get chemo again and it’s on your mind and that is one of the reasons I don’t sleep plus not having enough money fiancially to pay all bills because you can’t work and are on a fixed income which half the time you don’t even have enough money to pay bills or even get food so those are some of the stressful things going on so how do you get around that?

I’m sorry for this being so long of a response/question.
Most of my sleep issues revolve around getting into a very deep sleep. I think (although I’m really not 100% certain) most nights I get enough sleep, but I almost never feel as refreshed during the day as I did when I was in my preteen/early teen years (I’m 20 years old). I do believe can feel the effects of the sun on my circadian rhythm, as I often wake up feeling a bit more rested when it’s sunny early in the morning versus cloudy (sometimes I can even tell when I’m still in bed.)

I have been trying to do a better job at getting some deliberate sun exposure outside. While I’ll admit I haven’t been very consistent, I haven’t noticed much difference on nights following when I have.

What I’m wondering in my case is if the sun’s intensity is an issue when it comes to getting sun exposure. I’ve noticed the last two years I tend to sleep better in June, when the UV index is at its highest point. In fact, there were two days last June that I had my most refreshing nights in years. (I slept for 9 hours instead of my normal 7 to 7½, but I suspect this is because my sleep was so deep.) This was after spending 25-30 minutes outside doing cardio in the midday sun both times. But when I did the same thing at different points later in the summer, there was no impact to my sleep.

Does this sound legit that my body could be very dependent on the sun’s intensity for a deep sleep (and not just sun exposure itself), or do you think there must have been some other factor(s) in play? Whether those two nights last June were so refreshing because of the length of the sleep vs the deepness is also something I am left to ponder.

I have a question: I ‘ve been using liquid melatonin and have been gaining weight recently.. I am pudgier now than I was mid-winter when it was too cold to go for long walks, now the days are longer & I”m going for longer walks and I’m gaining.. what’s going on? I take melatonin as I’m 99% sure I have Delayed Sleep Phase syndrome (tried 2X to to sleep tests but failed as I didn’t sleep enough, only dozed, was told I don’t have sleep apnea though) I”m not overweight but I’ve gained about 15 pounds.. I eat paleo.

PS I only use 2 drops of melatonin as I’m very sensitive to stuff and this is maximum strength – I can feel those 2 drops! I’ve had paradoxical reactions to drugs in the past as well.

Any research out there on melatonin & weight gain? I’ve searched ….

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