Cortisol, blood sugar and sleep: what your body is doing at 3am
Many of the people I see in clinic fall asleep without much trouble. Then, somewhere in the small hours, they are suddenly wide awake with a mind that is fully switched on, and it can be five o'clock before they drift off again. This article explains how cortisol, blood sugar and sleep fit together, what your body is doing through the night, what in your day can knock that rhythm off course, and the habits I suggest to steady it.
Sleep is not a quiet time for your body
It is easy to think of the night as a pause. We fall asleep and nothing happens until the alarm. In fact your body does a great deal of work while you are unconscious.
Your liver is busy with its night shift, catching up on jobs it had no time for during the day. Your hormones are being adjusted all the time. Your brain is being fed and kept ticking over, and you are breathing without any help from you.
Two of those jobs matter most for the pattern in this article: the rise and fall of the hormone cortisol, and the steady delivery of fuel to your brain. When both run smoothly, you sleep through and wake ready for the day. When either one wobbles, you can find yourself wide awake at an hour that makes no sense.
If you have read my article on why you can't sleep and the three causes I look at first, this is the second of those three in more detail. The first was the nervous system, which I cover in tired but wired.
Cortisol: the hormone with a bad name
Cortisol is often called the stress hormone, and I think the label does it a disservice. Cortisol is essential. It supports your metabolism, your focus, your motivation and your energy, and it helps you get out of the way in times of danger.
What matters most is its timing. Cortisol follows a 24-hour rhythm set by your body clock, the circadian rhythm. It is meant to be higher through the morning and the day, which gives you the energy to do what you need to do. It then falls in the evening and stays low through the first part of the night. In the early hours, at around four to half past four for many people, it starts to climb slowly again so that you have what you need to get up and move around.
The key word is slowly. A healthy night has a steady, low-grade pace, with no big peaks and no deep troughs. Once you wake, cortisol rises further and reaches its peak in the first hour or so of the morning.
Blood sugar: how your brain is fed while you fast
The second player is blood sugar. Your brain runs mainly on glucose, and it needs a steady supply of it all the time, including at night. You are not eating while you sleep, so your body has to deliver that fuel from its own stores.
I want to be precise here, because some of the words sound alike. Glucose is the sugar circulating in your blood. Glycogen is the form your liver stores glucose in, a reserve for times between meals. Glycogen is a store and not a hormone. The hormone that tells your liver to release some of that reserve into the blood is glucagon. It works alongside insulin, which does the opposite job and brings glucose down after you eat. Through the night, with no food arriving, this pair keeps a modest, even trickle of glucose reaching your brain.
When that trickle is steady, you notice nothing. Your body has been doing it all your life.
Blood sugar and sleep: why your day shapes your night
What happens in the hours before bed, and across the whole day, shapes that supply through the night. Here is a day many people describe to me:
A rushed morning, with breakfast skipped or eaten on the move.
Meals that arrive late or not at all, because there is always something else to do.
More processed food than you would like, with plenty of sugar and refined carbohydrate.
Coffee or another stimulant to keep going.
An evening in which you are frazzled, so you pour a glass of wine or two.
A late evening meal that is heavy in carbohydrate, because the day left you no time to eat properly.
Most of us eat more refined carbohydrate than we realise, and eating a large amount of it late in the evening adds to the pattern. Together these habits give your blood sugar a rollercoaster shape through the day: surges when you eat something sugary, dips when you have not eaten for hours. Insulin and glucagon are working hard all that time to keep up.
Over weeks and months, that rollercoaster becomes the normal pattern. Then you go to bed, and the supply of glucose to your brain through the night inherits the same unevenness.
When the supply dips: where adrenaline comes in
Your brain watches its fuel supply closely. If the glucose reaching it falls, the brain reads that as an emergency and signals the adrenal glands, which sit on top of your kidneys, to release adrenaline. This is a well-established part of how the body responds to falling blood sugar.
Adrenaline is the fight-or-flight hormone. It raises your heart rate, sharpens your attention and releases stored glucose for fuel. It solves the fuel problem, and it wakes you up in the same moment. Once adrenaline is in your system, you are awake. Many people describe a pounding heart, a mind that is bang on and a feeling of alertness out of all proportion to the hour.
You can see why you do not want adrenaline arriving at three in the morning. It is a strong hormone, and it is built to override sleep.
I want to be straight with you about what is known. A fall in glucose triggering an adrenaline response is well-established physiology. How often it is the reason someone wakes at night, in people who do not have diabetes, is less clear, and research on it is limited. Many naturopaths link waking around 1 to 3am with the liver, and in my practice it often travels with blood sugar. I describe it here as a pattern I see often and one worth looking at. I do not present it as the cause of any one person's night, and I never read a cause into a clock time.
Is this your pattern?
Here is how it tends to look when people describe it to me:
You fall asleep reasonably well, often because you are exhausted.
Somewhere in the early hours, often between about two and four, you are suddenly wide awake and alert.
Your mind is switched on and you cannot get back to sleep until perhaps five o'clock.
The sleep you get after that is light, and then the alarm goes off for work.
The day before often included irregular meals, plenty of caffeine or sugar, and a drink or a late meal in the evening.
It helps to separate this from the pattern in tired but wired, where the difficulty is falling asleep in the first place. The two have different mechanisms, and a routine built for one will feel like a lot of effort for the other.
Waking in the small hours has many possible contributors. Alcohol, hormonal changes, an overheated bedroom, noise, medication, low mood and a disrupted body clock can all play a part, and some people have more than one going on. I go through the main ones in my article on waking at 3am.
Habits that keep the supply steady through the night
You have more influence over this than you might think, because the habits that matter happen in the daytime and the evening. Here is what I suggest.
Eat regularly through the day. Steady meals keep your glucose supply on an even keel. Many people find that skipping breakfast or lunch makes the evening harder.
Include protein at each meal. Eggs, fish, chicken, beans, lentils, tofu, Greek yoghurt, nuts and seeds all help, together with vegetables and whole grains for fibre. Protein and fibre slow the rate at which sugar reaches your blood.
Go gently on refined sugar and refined carbohydrate. White bread, pastries, biscuits and sweet drinks give the sharpest surges and dips.
Keep caffeine to the morning and early afternoon. Cutting it after midday for a couple of weeks is a useful test. I look at what coffee does to energy in why caffeine can leave you more tired.
Have your evening meal earlier and keep the carbohydrate portion modest. Eating a big carbohydrate-heavy dinner late in the evening adds to the pattern. I explain how evening digestion shapes the night in gut health and sleep.
Watch the evening drink. If people are wired, they often want a glass of wine to calm everything down. Alcohol is sedating, so it can help you fall asleep. Then your liver gets busy breaking it down, and while it is occupied, it is less able to release glucose into your blood. Alcohol also tends to make the second half of the night lighter and more fragmented. A slower evening routine gives you the calm without that cost.
Keep your meal times and your wake time steady. The body clock and the blood sugar rhythm both like a pattern.
People with diabetes, or who take medication that affects blood sugar, should follow their own care plan and speak to their GP or diabetes team before changing how they eat.
If you wake in the night, keep the lights low and leave your phone alone. Breathe in for four counts and out for six, softly and without strain, for about five minutes. A longer out-breath is a simple cue for your body to settle. If it makes you dizzy or more anxious, return to ordinary breathing.
Give any changes a few weeks of consistency before you judge them. The pattern built up over a long time, and it tends to ease over a long time too.
If you would like to run it as an experiment, try one week. Each morning, write down what time you woke in the night, if you did, and how you slept. Each evening, note when you ate your last meal, what was in it, when you last had caffeine and whether you had a drink. At the end of the week, look for the link between the two. You will have a much clearer picture of what moves the dial for you.
Herbs traditionally used alongside these habits
A herbal tonic can be a useful ally while new habits settle in, and I recommend it as one part of the picture. For this pattern I think about two things: how the day goes, and how the evening winds down. I use two tonics for the two jobs.
For the daytime, the herbs I choose are adaptogens, herbs traditionally used to support the body's resilience under strain. The four in Adrenal Guard are:
Holy Basil, or Tulsi (Ocimum tenuiflorum). Traditionally used in Ayurveda to support the body's response to everyday stress.
Siberian Ginseng (Eleutherococcus senticosus). Traditionally used in Russian and Chinese herbal medicine to support stamina and resilience under strain.
Cinnamon (Cinnamomum spp.). A warming herb with a long history of use alongside food, in both kitchen and herbal practice.
Gymnema (Gymnema sylvestre). Known in Ayurvedic tradition for its distinctive effect on the perception of sweet taste.
For the evening, the herbs are nervines, herbs traditionally used to support the nervous system and relaxation. The six in Sleep Deep are:
Passionflower (Passiflora incarnata). Traditionally used to support relaxation and a quieter mind in the evening. It has a long record in European herbal medicine.
Valerian (Valeriana officinalis). Traditionally used to support relaxation and healthy sleep patterns. It has been used in Europe for centuries.
Lemon Balm (Melissa officinalis). Traditionally used as a calming herb for restlessness, and a long-standing part of European herbal practice.
Lime Flower (Tilia × europaea). Traditionally used in European herbalism as an evening, relaxing tea.
Hops (Humulus lupulus). Traditionally used to support restful sleep. Hop pillows were a folk remedy for restless nights.
Lavender (Lavandula angustifolia). Traditionally used for its calming scent and as a relaxing evening herb.
I formulated Adrenal Guard to support daytime energy and the body's response to everyday stress, and Sleep Deep to support relaxation and healthy sleep patterns. Together they make up the Restore & Sleep duo, which carries the byline "for steady energy and deeper sleep": one tonic for the day and one for the evening. The product pages carry the full safety information, including who should speak to their GP before using them.
A tonic works best alongside the daytime and evening habits above. It supports the work you are already doing.
When to see your GP
Habit changes and herbs are for the ordinary, common pattern of waking in the night. Please book an appointment if:
your sleep has been disturbed for longer than three months, or you are struggling to function in the day
you wake with sweating, shaking or a pounding heart, especially if you have diabetes or take medication that lowers blood sugar
you have excessive thirst, unexplained weight loss or you are passing urine much more often than usual
you snore loudly, or someone has seen you stop breathing or gasp in your sleep
you feel low or anxious most of the time, or your mood has become heavy
you are taking prescribed sedatives, sleeping tablets or antidepressants, before you add any herbal product
you feel overwhelmed and unsafe. In that case please call NHS 111, or 999 in an emergency
Where this fits
Waking in the small hours has more than one possible cause, and the cortisol and blood sugar rhythm is one I see in many people. It sits alongside the nervous system pattern in tired but wired and the wider picture in my other sleep articles. If you would like to see where your own starting point might be, the EarthWise health quiz is a good place to begin.
Sarah Burt is a registered naturopath, medical herbalist and iridologist with 25+ years of clinical experience. All EarthWise tonics are formulated by Sarah based on her clinical protocols.
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This article is for informational purposes only and is not intended to diagnose, treat or cure any health condition. Always consult a qualified health practitioner before making changes to your health regimen.
