When something stressful happens — a difficult conversation, a near-miss in traffic, a deadline at work — your body does not just feel uncomfortable. It runs a full physiological programme called the stress response, involving your brain, your adrenal glands, and a cascade of hormones that affect nearly every system in your body. This programme is coordinated by something called the HPA axis, and if it is running at the wrong intensity or for too long, it affects everything from your sleep to your weight to your mood.
What the HPA Axis Actually Is
The HPA axis is short for the hypothalamic-pituitary-adrenal axis. It is the communication pathway between your hypothalamus (the part of your brain that monitors your environment), your pituitary gland (which sends signals to the rest of the body), and your adrenal glands (which sit on top of your kidneys and produce cortisol, the main stress hormone). When the hypothalamus detects stress, it tells the pituitary to send a signal to the adrenals, which respond by releasing cortisol. When the stress goes away, cortisol should drop back to normal, and the whole system should return to baseline.
The problem is that modern life does not always give the HPA axis the signal to switch off. Chronic psychological stress, poor sleep, inflammatory diets, blood sugar dysregulation, and constant notification pings all keep the stress response active when it should be resting. When this goes on for months or years, the HPA axis starts to dysregulate — sometimes producing too much cortisol, sometimes too little, sometimes the right amount at the wrong time of day.
Cortisol: Not Just a Stress Hormone
Cortisol has earned a reputation as the villain of human biology, but it is not inherently bad. It is essential for waking up in the morning, for maintaining blood sugar between meals, for managing inflammation, and for forming memories. The issue with cortisol is not its existence — it is its pattern. A healthy cortisol curve starts high in the morning (helping you get going), declines steadily through the day, and reaches its lowest point around midnight. When this curve is flattened or inverted, the downstream effects on health are significant.
High cortisol at night disrupts sleep architecture, suppresses the gut immune system, impairs memory consolidation, and contributes to weight gain around the midsection. Low cortisol in the morning produces difficulty waking, fatigue that is not relieved by sleep, and a flattened stress response that makes ordinary challenges feel overwhelming. Both patterns are increasingly common, and both respond to interventions that address the underlying drivers of HPA axis dysregulation.
What You Can Do Today
Sleep is the most powerful HPA axis regulator available. Getting consistent, adequate sleep (7 to 9 hours, same schedule every night) does more for HPA axis health than any supplement or intervention. Blood sugar stability during the day — not skipping meals, not eating high-sugar foods that spike and crash insulin — significantly reduces the chronic HPA axis activation that comes from metabolic stress. Ashwagandha, an adaptogenic herb, has good evidence for normalising cortisol patterns in chronically stressed adults at 300 to 600mg daily of KSM-66 extract.
There is a chain of command inside your body that most people have never heard of, but it runs every time you feel stressed, every time you wake up in the morning, and every time you struggle to fall asleep at night. It is called the HPA axis, and if it is switched on at the wrong times or running for too long, it quietly drives some of the most common health complaints people bring to their doctors — poor sleep, weight gain around the middle, anxiety, exhaustion that sleep does not fix, and difficulty concentrating. This is not about being too sensitive or not trying hard enough. It is about biology.
The Three-Part System That Controls Your Stress Response
The HPA axis is short for the hypothalamic-pituitary-adrenal axis. Say that three times fast and you will forget why you started, which is fitting because it is not complicated once you break it down. The hypothalamus is a small region at the base of your brain that monitors what is happening in your body and your environment. The pituitary is a pea-sized gland that hangs below it, and it is essentially the body’s control centre, sending signals to the rest of the organs. The adrenal glands are two small glands that sit on top of your kidneys, and they produce cortisol — the main stress hormone.
When the hypothalamus detects stress — and it reads all kinds of stress, not just emotional but metabolic stress from unstable blood sugar, inflammatory stress from poor gut health, and physical stress from sleep deprivation — it signals the pituitary. The pituitary then tells the adrenal glands to release cortisol. Cortisol is useful in the short term. It gives you energy, sharpens your focus, and mobilises glucose for action. When the stress goes away, cortisol should fall back to baseline. That is the normal cycle.
The problem is that modern life keeps the HPA axis running when it should be resting. Blood sugar spikes and crashes, poor sleep, chronic work stress, inflammatory diets, even the constant checking of your phone — all of these keep the system activated. When the hypothalamus keeps firing the alarm signal day after day, the HPA axis starts to behave abnormally. Sometimes it produces too much cortisol at night when it should be low. Sometimes it starts producing too little in the morning when you need it most. Sometimes it responds normally to stress but fails to switch off properly when the stress is gone. All of these patterns are associated with the same cluster of symptoms.
Why Cortisol at the Wrong Time Is Worse Than High Cortisol
Cortisol is not the enemy. You need it. The issue is pattern. A healthy cortisol rhythm looks like a descending slope: highest in the first hour after waking (helping you get going), declining steadily through the afternoon and evening, lowest around midnight. This rhythm is called the cortisol awakening response, and it is one of the most reliable markers of HPA axis health.
When cortisol is high at night instead of low, several things happen. Sleep becomes fragmented — you fall asleep fine but wake at 2 or 3am with your mind racing. The gut immune system, which is regulated by cortisol, becomes suppressed, contributing to dysbiosis and gut permeability. Memory consolidation during sleep is impaired, so even adequate sleep hours leave you not feeling rested. Blood sugar regulation worsens because cortisol is insulin-antagonistic. And the fat storage pattern shifts toward the midsection because cortisol promotes visceral fat accumulation specifically.
When cortisol is too low in the morning, waking feels impossible. You need caffeine to get going, and even then the energy is fragile. Ordinary stressors — a difficult email, a traffic jam — feel disproportionately overwhelming. This is the burnout pattern, and it is increasingly common in high-performing people who have been running on adrenaline and poor sleep for years.
How to Tell If Your HPA Axis Needs Attention
The most informative test is a four-point salivary cortisol test, which measures cortisol at waking, 30 minutes after waking, noon, and bedtime. This is not a standard NHS test, but it is available through functional medicine practitioners and some private labs. The pattern it reveals tells you far more than a single cortisol blood test ever could.
Without testing, the clues are in the pattern. If you cannot wake up without caffeine, if you crash in the afternoon, if you wake at 3am with a racing mind, if stress feels overwhelming in ways it did not use to — these are all flags. The good news is that HPA axis dysregulation responds well to the basics: consistent adequate sleep, blood sugar stability, stress management, and targeted nutritional support.
What You Can Do Today
The foundation is sleep — the same time every night, 7 to 9 hours, no screens in the hour before bed. Blood sugar stability during the day matters more than most people realise: eat protein and fat with every meal, avoid high-sugar foods that spike and crash insulin, and do not skip breakfast if you struggle with energy in the morning. If you are under chronic stress, ashwagandha at 300 to 600mg daily of KSM-66 extract has good evidence for normalising cortisol patterns. This is not about reducing cortisol to zero. It is about restoring the proper pattern so cortisol is high when you need it and low when you do not.
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