What is cortisol?
Cortisol is your body's main stress hormone. It's produced by your adrenal glands and plays a role in nearly every system in your body — from how you wake up in the morning to how your immune system fights off infections. In short bursts, cortisol is actually helpful: it sharpens your focus, gives you energy, and helps you respond to challenges.
The problem isn't cortisol itself — it's what happens when it stays elevated for too long. Chronic stress keeps cortisol high day after day, and that's when it starts causing damage to your sleep, metabolism, immune system, and mood.
Why it matters for longevity
Healthy cortisol follows a natural daily rhythm called the diurnal curve. It's highest in the morning (helping you wake up alert) and gradually drops through the day, reaching its lowest point at night (allowing you to fall asleep). This rhythm is a sign that your body is well-regulated.
Chronic stress flattens this curve. Cortisol stays elevated in the evening when it should be low, and may not rise enough in the morning. Over time, this pattern is linked to weight gain (especially around the belly), poor sleep, weakened immunity, higher blood sugar, and increased . Research has also connected chronically high cortisol to accelerated aging at the cellular level.
Women are particularly susceptible to HPA axis dysregulation — the feedback loop between the brain and adrenal glands that controls cortisol. Hormonal shifts during the menstrual cycle, perimenopause, and postpartum can make women more sensitive to stress-related cortisol disruption. This is one reason why stress, sleep problems, and belly fat often cluster together for women.
What the numbers mean
Cortisol is typically measured in the morning, when it should be at its highest:
- Conventional range (morning): 6–23 ug/dL
- Optimal range (morning): 10–18 ug/dL
A very high morning cortisol (above 20 ug/dL) may suggest chronic stress or a condition worth investigating. A very low morning cortisol (below 6 ug/dL) could indicate adrenal fatigue or insufficiency — your adrenals may be struggling to keep up after prolonged stress.
A single morning reading is a starting point, but it doesn't tell the whole story. For a complete picture of your daily rhythm, some practitioners use a 4-point salivary cortisol test that measures levels at morning, midday, afternoon, and bedtime.
What affects your cortisol
- Psychological stress: Work pressure, relationship issues, financial worry, and constant overstimulation all keep cortisol elevated. Your body can't tell the difference between a real threat and a stressful email.
- Sleep deprivation: Poor sleep raises cortisol the next day, and high cortisol makes it harder to sleep — creating a vicious cycle that's hard to break.
- Overtraining: Too much intense exercise without proper recovery raises cortisol chronically. This is common in women who do excessive high-intensity cardio without rest days.
- Blood sugar swings: Skipping meals or eating lots of refined sugar causes blood sugar crashes, which trigger cortisol spikes as your body tries to stabilize.
- Caffeine: Coffee and energy drinks directly stimulate cortisol release. Drinking caffeine late in the day can disrupt the natural cortisol decline you need for good sleep.
- Inflammation: Chronic inflammation (which you can track with hs-CRP) both raises and is raised by cortisol, creating another feedback loop.
How to get tested
A morning serum cortisol test is the most common option. Blood should be drawn early in the morning (ideally between 7–9 AM) when cortisol is naturally highest. It does not require fasting, but you should avoid intense exercise the morning before the test. For a more detailed picture of your daily rhythm, ask your doctor about a 4-point salivary cortisol test — you collect saliva at four times throughout the day, which maps out your full curve.
How to improve it
- Get morning sunlight. Exposure to bright light within the first 30–60 minutes of waking helps set a strong cortisol peak in the morning, which supports the natural decline through the day.
- Build a wind-down routine. Dim the lights, put screens away, and do something calming in the 1–2 hours before bed. This helps cortisol drop to the low levels needed for restorative sleep. Use our Sleep Calculator to find the right bedtime for your schedule.
- Move gently when stressed. When cortisol is already high, a walk, yoga, or light stretching is better than another intense HIIT session. Save the hard workouts for days when you feel recovered.
- Eat regular, balanced meals. Stable blood sugar means fewer cortisol spikes. Include protein, healthy fats, and fiber at each meal. Avoid going too long without eating.
- Limit caffeine after noon. If you're struggling with sleep or evening anxiety, moving your coffee cutoff to before noon can make a noticeable difference in your cortisol curve.
- Protect your . Cortisol and DHEA-S are made from the same precursors. When cortisol stays chronically high, DHEA-S often drops. Supporting both sides of this equation — lowering stress while nourishing your adrenals — gives the best results.