The Cortisol Clock

Do you wake up exhausted, struggle through an afternoon slump, then feel wide awake at 11pm, mind racing? Or wake at 3am and can't get back to sleep? You may be feeling the effects of a rhythm you've probably never thought about: the daily rise and fall of your stress hormone, cortisol.

Meet cortisol

Cortisol has a bad reputation as "the stress hormone", but it's essential for life. Made by the adrenal glands, which sit on top of the kidneys, it raises blood sugar to give you energy, helps control blood pressure, calms inflammation, sharpens memory and gets you up and moving in the morning. (See Balancing the Sugar Seesaw.)

Its release is controlled by the HPA axis, a chain of command running from the hypothalamus in the brain, to the pituitary gland, to the adrenal glands. When the brain senses a challenge, it sends a signal down the chain, and cortisol is released. When the challenge passes, cortisol tells the brain to switch the signal off again. It's a beautifully balanced feedback loop, as long as it gets the chance to switch off.

A hormone that keeps time

Cortisol follows a daily rhythm, set by the master clock in your brain, which is tuned mainly by light:

• Early morning: cortisol begins to climb in the small hours, preparing you to wake.
• On waking: it surges by around 50–75% in the first 30 to 45 minutes after you wake up. This "cortisol awakening response" is your natural get-up-and-go.¹
• Through the day: levels gradually fall, with small rises after meals and moments of stress.
• Evening and night: cortisol drops to its lowest point around midnight, while the sleep hormone melatonin rises, so you can rest and repair.

A healthy rhythm is like a ski slope: high in the morning, gliding smoothly down to a low point at night.

Cortisol isn't the enemy. It's a rhythm, and health depends on keeping it in time.

When the clock goes wrong

Long-term stress, poor sleep, late nights, shift work, blood sugar swings and too little daylight can all knock this rhythm out of shape. Instead of a smooth slope, the curve can flatten: too low in the morning, so you can't get going, and too high at night, so you can't switch off. (See Living by the Sun.)

This matters. A review of 80 studies found that a flatter daily cortisol rhythm was linked with poorer health across the board, both mental and physical.² In a study of more than 4,000 UK civil servants, those with the flattest rhythms had nearly twice the risk of dying from heart disease over the following years.³

How stress shows up in the body

• Energy and blood sugar. Cortisol raises blood sugar. When it stays high, the body can become less sensitive to insulin, setting the scene for energy crashes and cravings.
• Weight around the middle. Fat cells around the abdomen are especially responsive to cortisol. Women who carry more weight around their middle tend to release more cortisol under stress.⁴
• Immunity and healing. In a famous study, wounds took 24% longer to heal in people under the long-term stress of caring for a relative with dementia.⁵
• Sleep. Raised evening cortisol makes it hard to fall asleep, and poor sleep raises cortisol further. After a night of lost sleep, evening cortisol was around 40% higher the next day.⁶
• Mood and memory. The hippocampus, the brain's memory centre, is packed with cortisol receptors and is sensitive to long-term stress. (See Where Body Care Meets Mind.)
• Digestion and hormones. Under stress, the body puts digestion and reproduction on hold, which can show up as bloating, irregular cycles or low libido.

What about "adrenal fatigue"?

You may have heard the term "adrenal fatigue": the idea that the adrenal glands become worn out by stress. Doctors don't recognise it as a diagnosis, and studies haven't found that the glands themselves "run out".⁷ But the symptoms people describe are very real. A more accurate way to describe them is HPA axis dysregulation: the brain's control of cortisol has fallen out of rhythm, rather than the glands having failed.

Rare but serious conditions, such as Addison's disease or Cushing's syndrome, can also affect cortisol, so persistent symptoms should always be checked by your GP. A practitioner may also suggest a salivary or urine cortisol test, taken at several points through the day, to map your own personal rhythm.

Resetting your rhythm

Morning

• Get outside within an hour of waking. Bright morning light is the strongest signal to set your body clock and boost a healthy cortisol rise. Even a cloudy day outdoors is far brighter than indoor light.
• Wake at the same time every day, including weekends.
• Eat a breakfast with protein, such as eggs, yoghurt, nuts or seeds, to keep blood sugar steady.
• Have caffeine after food, not instead of it, and none after midday. Caffeine taken even six hours before bed can cut sleep by more than an hour.⁸

Daytime

• Eat regular, balanced meals to avoid the blood sugar dips that trigger cortisol.
• Move. Exercise earlier in the day suits the cortisol rhythm best. If you're exhausted, choose gentle walking, yoga or swimming over punishing workouts.
• Take mini breaks. Just five minutes a day of "cyclic sighing", two breaths in through the nose and a long, slow breath out, improved mood and calmed breathing more than meditation in one study.⁹ (See The Healing Breath.)
• Spend time in nature. Twenty to thirty minutes outdoors brings a measurable drop in cortisol.

Evening

• Dim the lights after sunset, and put screens away an hour before bed. Reading on a light-emitting device before bed has been shown to delay melatonin and the body clock.¹⁰
• Wind down with a warm bath, gentle stretching, reading or meditation. (See The Sound of Stillness.)
• Eat your last meal two to three hours before bed.
• Keep your bedroom cool, dark and quiet, and aim for seven to nine hours of sleep. Darkness lets melatonin, cortisol's night-time partner, rise as it should. (See The Art of Sleep.)

Nutrients and herbs that help

• Magnesium, found in leafy greens, nuts, seeds and dark chocolate, is used up faster under stress and supports relaxation and sleep.
• Vitamin C. The adrenal glands hold some of the highest concentrations of vitamin C in the body. In one study, high-dose vitamin C helped people's blood pressure and cortisol recover more quickly after a stressful task.¹¹
• Omega-3 fats from oily fish may help soften the body's stress response.
• Ashwagandha. In adults under chronic stress, this calming adaptogen lowered cortisol levels by around 28% over two months.¹² (See The Inner Life of Plants.)
• Rhodiola. In people with stress-related exhaustion, rhodiola lowered the morning cortisol surge and eased fatigue.¹³
• Eleuthero (Siberian ginseng), studied for decades by Soviet scientists in athletes, workers and cosmonauts, is a steadying adaptogen for long periods of strain, gentle enough for most people.
• Schisandra, the "five-flavour berry" of Chinese medicine, is traditionally used to calm the mind while sharpening focus, and to support the liver. Russian researchers studied it alongside eleuthero for endurance and mental performance under stress.¹⁴
• Holy basil (tulsi), a revered herb in Ayurveda, is traditionally used to bring calm and resilience, and makes a lovely daily tea.
• Liquorice helps cortisol last longer in the body, so it's traditionally used when energy is low, but it can raise blood pressure and isn't suitable for everyone.

Which herbs are right depends on your pattern and your energetics. Someone who is wired, hot and anxious needs very different support from someone who is flat, cold and depleted, and the wrong herb can make things worse. To learn more, read The Architecture of Balance.

For accuracy and safety, it's best to seek guidance from a qualified practitioner rather than self-prescribing. They'll identify your pattern, check for interactions with any medicines, and choose the right herbs and doses for you.

At Rootwise, we look at the whole of your day: your sleep, stress, meals, energy and, where helpful, your cortisol rhythm through testing. Then we build a plan, with lifestyle changes, nutrition and herbs, to help bring your rhythm, and you, back into balance.