Cortisol is a steroid hormone produced by your adrenal glands, two small glands that sit on top of your kidneys. Often called the “stress hormone,” cortisol does far more than manage stress. It regulates how your body uses energy, controls inflammation, influences blood pressure, and helps keep you alert on a daily cycle. Your cortisol levels naturally peak around 8 a.m. and drop to their lowest point around 3 a.m., rising again before you wake.
How Your Body Makes Cortisol
Cortisol production starts in your brain. When your body needs more cortisol, whether because of stress, low blood sugar, or simply because it’s morning, your hypothalamus releases a signaling hormone that travels to your pituitary gland. The pituitary responds by sending its own hormone into your bloodstream, which reaches your adrenal glands and triggers the outer layer (the adrenal cortex) to produce and release cortisol.
This three-step chain, from hypothalamus to pituitary to adrenal glands, has a built-in off switch. Once cortisol levels in your blood rise high enough, that cortisol signals your hypothalamus to stop the process. This feedback loop keeps cortisol within a healthy range throughout the day, preventing your body from making too much or too little.
What Cortisol Does
Cortisol touches nearly every organ system. Its most important jobs fall into a few categories.
Energy and Blood Sugar
Cortisol is your body’s energy manager. It tells your pancreas to lower insulin (which pulls sugar out of blood) and raise glucagon (which pushes sugar into blood). It also triggers your liver to release stored glucose for quick fuel. This is especially useful during stress, when your muscles and brain need immediate energy. Cortisol also influences how your fat tissue, liver, and muscles use and store glucose throughout the day.
Inflammation and Immunity
In short bursts, cortisol strengthens your immune response by limiting inflammation. This is why synthetic versions of cortisol are used to treat inflammatory conditions. But this immune-calming effect only works well when cortisol spikes are brief. When cortisol stays elevated for weeks or months, the immune system can become suppressed rather than supported.
Blood Pressure
The exact mechanism isn’t fully understood, but cortisol plays a clear role in blood pressure regulation. Elevated cortisol can cause high blood pressure, and abnormally low cortisol can cause blood pressure to drop.
Cortisol and the Stress Response
When your brain perceives a threat, your nervous system fires first, releasing adrenaline for an immediate reaction. Cortisol arrives as the second wave. It keeps the body in a heightened state for longer, maintaining elevated heart rate and blood sugar so you can deal with whatever triggered the alarm. Once the threat passes, cortisol levels drop and your body returns to baseline.
The trouble comes when that stress response never fully shuts off. Chronic stress, whether from work, relationships, financial pressure, or illness, can keep cortisol elevated for extended periods. This leads to some unwelcome changes. Elevated cortisol increases appetite, particularly for calorie-dense foods, and promotes fat storage. Over time, this contributes to weight gain, especially around the midsection. Chronically high cortisol is also linked to high blood pressure, impaired memory, weakened immunity, and disrupted sleep.
What Happens When Cortisol Is Too Low
Too little cortisol creates its own set of problems. The most common cause of low cortisol is suddenly stopping corticosteroid medications after taking them for a long time. When you take these medications, your body dials down its own cortisol production. Stopping abruptly leaves a gap before your adrenal glands can ramp back up.
Addison’s disease is a rarer cause, where the immune system attacks the adrenal glands themselves. In developed countries, autoimmune damage accounts for 8 or 9 out of every 10 cases. Tuberculosis, certain genetic conditions, and pituitary gland problems can also lead to low cortisol production.
The symptoms of low cortisol develop gradually and can be hard to pin down: chronic fatigue, muscle weakness, loss of appetite, weight loss, and abdominal pain. Many people also experience low blood pressure that drops further when standing, causing dizziness. Cravings for salty foods, irritability, depression, and low blood sugar are common. People with Addison’s disease sometimes develop noticeable darkening of the skin, particularly on scars, skin folds, knuckles, and the inside of the cheeks.
Your Daily Cortisol Rhythm
In a healthy person, cortisol follows a predictable 24-hour cycle. Levels climb in the early morning hours, reaching their peak around 8 a.m. to help you wake up and feel alert. From there, cortisol gradually declines throughout the day, dropping to roughly half its morning level by 4 p.m. and hitting its lowest point around 3 a.m. This rhythm is one reason you feel most energized in the morning and naturally wind down at night.
Disrupting this cycle, through shift work, chronic sleep deprivation, or sustained stress, can throw off energy levels, mood, and metabolism. Sleep deprivation in particular can raise cortisol levels, which in turn impairs memory, promotes weight gain, and may accelerate aging.
How Cortisol Levels Are Tested
Because cortisol fluctuates so much throughout the day, testing requires careful timing. A blood test is the most common method, typically drawn twice: once in the morning when levels are highest, and again around 4 p.m. when they’re much lower. Normal morning levels generally fall between 10 and 20 mcg/dL, while afternoon levels range from 3 to 10 mcg/dL.
Saliva tests offer a more convenient alternative, especially for tracking how cortisol rises and falls over the course of a day. Your provider may ask you to collect several saliva samples at home at different times. Urine testing takes a different approach, measuring total cortisol output over a full 24-hour period by collecting all urine produced during that window. Each method gives a slightly different picture, and the choice depends on what your provider is looking for.
Lifestyle Factors That Influence Cortisol
For people without a medical condition causing abnormal cortisol, daily habits have a meaningful effect on how much cortisol your body produces. Physical activity is one of the most reliable ways to bring cortisol down, with studies showing benefits particularly in older adults and people with depression. A balanced, plant-heavy diet like the Mediterranean diet provides the nutritional foundation for healthy stress management.
Mind-body practices have solid evidence behind them. Mindfulness-based stress reduction therapy has been shown to lower both cortisol levels and subjective feelings of stress. Yoga can reduce cortisol along with heart rate and blood pressure. Even simple breathing exercises make a measurable difference.
Time spent outdoors matters more than most people realize. The practice of “forest bathing,” spending time in wooded areas and breathing the air, has been shown to reduce cortisol. Even a 10-minute walk in a natural setting can lower stress levels. Herbal teas like chamomile and lemon balm are generally safe options that may help take the edge off, though supplements like ashwagandha or rhodiola are worth discussing with a provider before trying.
Sleep may be the single most important factor. Poor sleep raises cortisol, and elevated cortisol makes it harder to sleep, creating a cycle that compounds over time. Prioritizing consistent, adequate sleep breaks that cycle and gives your cortisol rhythm the best chance of functioning normally.