Why Stress Is Spiking Your Blood Sugar: The cortisol-glucose connection
Something I see, day in day out, in my clinic is blood sugar dysregulation. Whether this is concluded due to thorough case-taking or symptomology, or a client has had a blood test (fasting blood sugar, Hb1Ac and/or fasting insulin), or they have used a CGM (continual blood glucose monitor), and can see they have an elevated average blood sugar level, the questions remain the same….
First, the obvious one, would be to look into diet. There is the possibility that people won’t be completely forthcoming in disclosing their dietary habits, especially around snacking! And this isn’t just the obvious, ie chocolate, lollies, ice-cream, cakes, cookies, sweet drinks (including honey - sorry!) etc. it can be things like rice cakes and ‘empty’ carbs - meaning carbohydrates eaten without being ‘dressed’ with fats and protein. So its not always about the carbs, its HOW and WHEN you eat the carbs. (that’s a story for another day!)
90% of the time, the people that come to see are pretty health-conscious, fit and active. Their diet looks incredibly balanced and healthy…. So… why do they have elevated blood sugar and/or insulin??
Therefore, secondly, we need to look at lifestyle. Mainly , the most eye-rolling topic in clinic - Stress.
urhh, I feel you… no-one really wants to talk about “stress’ - (whatever that actually means anyway?) Stress is insidious. Who isn’t stressed really? our resilience differs, between individuals and within different circumstances of our lives.
And yet, stress is one of the most overlooked drivers of blood sugar imbalance. At the centre of this is cortisol — the body's primary stress hormone — which has a profound and direct effect on glucose levels. Understanding how this works can change the way you approach your energy, mood, and metabolic health.
What cortisol actually does
Cortisol is produced by the adrenal glands (two small glands that sit on top of your kidneys) in response to stress — whether that stress is physical, emotional, or psychological (read that again!). In the short term, it's helpful: cortisol signals the liver to release glucose into the bloodstream, giving your body a fast burst of energy to deal with the threat.
This process — called gluconeogenesis — was designed for acute, short-lived stress (think: running from danger). The problem is that modern life dilivers a near-constant stream of stressors, keeping cortisol elevated day after day.
Chronic high cortisol essentially tells your body to keep producing glucose — even when you don't need it. Over time, this can lead to persistently elevated blood sugar, insulin resistance, and increased risk of type 2 diabetes.
I can tell you a story about this, I did my own CGM experient quite a while ago (highly recommend doing this! I used Vively). My blood sugar tended to be on the low side at times, but the most significant spike I had was walking around IGA , completely overwhelmed during a busy time ;) = stress. it had nothing to do with what I ate that day. The other notable time was after a smoothie, which in hindsight maybe didn’t have enough protein, OR perhaps it was that I didn’t ‘chew’ my smoothie (which you absolutely should!) so my enzymes would not have been working properly or preparing my body well for the fuel it was about to receive. tip: chew your smoothies! don’t make them too cold, and sip/chew them slowly! don’t wolf them down in 2 seconds flat like I do!
Cortisol and your body clock
Here's where things get interesting. Cortisol doesn't just respond to stress — it also follows a natural 24-hour rhythm. Levels are lowest in the first couple of hours after you fall asleep, then gradually rise through the night, peaking just after you wake up. (It works in reverse balance with Melatonin- think of it like a seesaw). This morning surge is intentional: it primes your body for the day ahead. It is your ‘get up and go’. This is called the Cortisol Awakening Response (CAR). You can actually test this pattern. We want a healthy CAR.
When this rhythm is disrupted — by poor sleep, shift work, irregular schedules, poor melatonin production, or chronic stress — the knock-on effects on blood sugar can be significant. Your liver, pancreas, and fat tissue all have their own internal clocks that work in sync with your cortisol rhythm. Disrupt one, and you disrupt all of them.
Night shift workers are a good example: circadian disruption alters hormone secretion, appetite, and energy use — all of which push blood sugar in the wrong direction. This is well and truly documented.
The blood sugar rollercoaster
When cortisol stays chronically elevated, cells become less responsive to insulin — a condition called insulin resistance. Your pancreas responds by producing more insulin, but eventually it can't keep up, or the signals (hormones) don’t have the same response from the receptors/cells. when someone keeps banging on the door, and we are pre-occupied and have more important things to do, we tend to ignore the noise. The result: blood sugar stays high, (it doesn’t get into the cell), energy crashes, sugar cravings intensify, and you reach for something sweet or caffeinated — which temporarily spikes glucose before sending it plummeting again.
This cycle is exhausting, both physically and hormonally. And it places ongoing stress on the adrenal glands, perpetuating the problem.
Conversely, low cortisol (as seen in adrenal fatigue) creates the opposite issue: the liver struggles to convert stored glycogen into usable glucose, leading to hypoglycaemia — symptoms of which include brain fog, irritability, headaches, and shakiness that many people mistakenly attribute to hunger alone.
What you can do about it
The good news: small, consistent lifestyle changes can meaningfully support both cortisol balance and blood sugar stability.
Morning light : Get outside within an hour of waking. Natural light helps reset your body clock and improve sleep quality.
Balanced meals: Pair complex carbs with protein and healthy fats. Eat at consistent times to support circadian rhythm.
Stress management (groan!) Mindfulness and meditation have been shown to measurably lower cortisol levels (look up mindfulness based stress reduction MBSR). I did this course during my 450hr Yoga teacher training and it was insightful. Other ideas that may work for you: a short walk, 2min of connected breathwork or the 4-7-8 breath *0r simply a longer exhale than the inhale. Taking some unnecessary things off your plate. Talking to someone about what’s on your mind. Journalling. Exercise!
Regular movement: Exercise improves insulin sensitivity, lowers cortisol, and promotes deeper sleep — a triple win.
Consistent sleep: Same bedtime, same wake time. Regularity protects your circadian rhythm more than any supplement.
Key nutrients: Omega-3s, magnesium, vitamin C, and B vitamins all support healthy cortisol production and stress response.
Herbal Medicine: Different herbs have different effects for different people. check out my post on Adaptogens and Nervines, but more importantly - see a herbalist!
Check out my free blood sugar balancing guide HERE
The Mediterranean Diet connection
If you'd rather not track individual nutrients, a Mediterranean-style eating pattern covers a lot of bases. Rich in whole grains, vegetables, legumes, fish, and olive oil, it's been shown to support healthy blood glucose, reduce cortisol, improve sleep quality, and nourish a diverse gut microbiome. It's also naturally high in melatonin — a key regulator of your circadian rhythm. yes- some plants contain melatonin!
The bottom line
Stress, sleep, and blood sugar are more intertwined than most people realise. Cortisol/Adrenaline is the thread that connects them all. By supporting healthy sleep habits, managing stress proactively, eating nourishing foods at regular times, and moving your body daily, you're not just managing stress — you're actively protecting your metabolic health.
If you suspect your blood sugar swings are driven more by stress than diet, it's worth talking to a healthcare practitioner and exploring whether adrenal function may be a factor.
AND - its worth noting - if you have high blood sugar on your blood test results (think >5), and your diet is balanced - please don’t stress about not being ‘good enough’! the most helpful thing you can do, is more self-kindness! It goes a long way!
Reach out if you need any support.
Love Em