Cortisol Gets a Bad Rap: Why The "Stress Hormone" Is Essential for Health
Cortisol plays such a vital role in your body that it deserves more than a quick mention. This is the first in a two-part exploration of this essential hormone.
Cortisol is a steroid hormone produced by the adrenal glands and is often called the body’s primary “stress hormone.” While it’s best known for its role in the fight-or-flight response, cortisol has far broader responsibilities. It follows a natural daily rhythm and is essential for waking us up in the morning, regulating metabolism, managing inflammation, and helping the body respond to both physical and emotional challenges.
Historically, cortisol has gotten a bad rap because consistently high levels, often due to chronic psychological stress, can lead to what scientists call a high allostatic load. This refers to the cumulative wear and tear on the body that occurs when stress responses are triggered too frequently or for too long. Over time, this burden can negatively affect metabolism, immune function, and overall well-being.
But cortisol itself is not harmful when it stays within a healthy rhythm. In fact, it is a key part of how our bodies stay resilient and balanced. Let’s take a closer look at how cortisol supports stress response, metabolism, immune health, and its essential role in your Circadian Health.
The Clock: Circadian Rhythm of Cortisol
One of cortisol’s most important roles is serving as a messenger for the body’s internal clock. Its levels follow a strong circadian rhythm, rising and falling in roughly a 24-hour cycle. Under normal conditions, cortisol peaks in the early morning around the time you wake up, helping you feel alert and energized. From there, levels gradually decline throughout the afternoon and reach their lowest point late in the evening and during the early part of the night. This rhythm is driven by the brain’s master clock, the suprachiasmatic nucleus (SCN) in the hypothalamus, which helps align hormone production with the light-dark cycle of the environment.
So, why does cortisol spike in the morning? It’s the body’s natural way of preparing for the day ahead. This rise, known as the cortisol awakening response, helps increase blood sugar and boost alertness. You can think of it as your body’s own caffeine. By evening, lower cortisol levels support the transition to rest and sleep.
Cortisol also plays a key role in keeping the body’s internal systems coordinated. Each organ has its own rhythm, and cortisol acts as a signal that helps synchronize them to the central clock. For example, the morning rise cues the liver and fat tissues to begin releasing energy. When this rhythm is disrupted, such as by shift work, jet lag, or irregular sleep, it can throw off metabolism and hormone balance (1). Maintaining a steady cortisol pattern is essential for overall Circadian Health.
Cortisol Throughout Your Body
Cortisol is far-reaching, influencing almost every major system in the body. Its effects vary depending on context, timing, and levels and scientists are still uncovering nuances of its actions.
Immune System: Protecting Your Body & Modulating Inflammation
Cortisol plays a key role in controlling the immune response. When cortisol levels increase during stress or as part of its natural rhythm, it signals immune cells to reduce the release of inflammatory molecules. This helps prevent excessive inflammation that could harm healthy tissues. Cortisol suppresses cytokine production and slows immune cell activity, which is why corticosteroids like prednisone and hydrocortisone are used to treat autoimmune flare-ups, asthma, and allergic reactions.
Clinically, cortisol and its synthetic forms are widely used for their anti-inflammatory properties. For example, 1% hydrocortisone cream can ease redness and itchiness in eczema, while oral steroids help reduce joint inflammation in conditions like rheumatoid arthritis. While short-term cortisol spikes during stress or exercise may support immune surveillance, chronically elevated cortisol can suppress immunity. This is seen in conditions like Cushing’s syndrome, where people are more prone to infections. Conversely, cortisol deficiency, such as in Addison’s disease, can lead to an overactive immune response, increasing the risk for autoimmune conditions. Maintaining cortisol balance is essential for a responsive but not overactive immune system.
Nervous System: Memory and Mood
Cortisol significantly influences the brain, particularly regions involved in memory and emotion such as the hippocampus and amygdala. Moderate increases in cortisol during emotionally intense moments can help cement strong memories. However, consistently high cortisol levels can impair memory function and are linked to mood disorders such as anxiety and depression. On the other end of the spectrum, very low cortisol levels may cause fatigue, brain fog, and low mood. This reflects the brain’s sensitivity to both excess and deficiency of cortisol. The presence of glucocorticoid receptors in the brain explains why this hormone has such a pronounced effect on mood, focus, and overall mental clarity.
Cardiovascular System: Blood Pressure and Circulation
Cortisol supports cardiovascular function by helping maintain blood pressure. It does this by making blood vessels more responsive to catecholamines, such as adrenaline (2). Without cortisol, vessels are less able to constrict, which can lead to dangerously low blood pressure. This is one reason why severe cortisol deficiency, as seen in adrenal crisis, can result in hypotension. Cortisol also affects the kidneys by promoting sodium retention, contributing to blood volume. Although aldosterone is the primary regulator of salt balance, cortisol plays a supporting role. While these effects help ensure adequate circulation during stress, consistently high cortisol can contribute to the development of hypertension over time.
Skeletal and Integumentary Systems: Bone and Skin
Cortisol impacts both bone and skin health. It reduces bone formation and decreases calcium absorption, which can lead to weakened bones over time (3). This is a common concern with long-term corticosteroid therapy, where patients may develop osteoporosis. In the skin, elevated cortisol levels can impair collagen production, leading to thinner skin and easier bruising. These effects are typically seen with chronic cortisol excess rather than daily fluctuations. Nevertheless, they illustrate how cortisol can influence the structure and resilience of the body’s connective tissues.
Endocrine and Developmental Systems: Growth and Hormonal Balance
Cortisol plays an important role in fetal development, particularly in preparing the lungs for birth. A surge in cortisol near the end of pregnancy helps trigger the production of surfactant, a substance that keeps the lungs open after birth (4). For this reason, doctors sometimes administer corticosteroids to pregnant women at risk of preterm labor to support the baby’s lung development. Beyond development, cortisol interacts with several other hormones. It can counteract insulin, enhance the effects of glucagon and adrenaline, and influence thyroid and reproductive hormone activity. Cortisol’s natural rhythm also affects behaviors such as appetite, energy levels, and physical performance. These wide-ranging interactions show that cortisol is deeply woven into many of the body’s essential systems.
Keeping Cortisol in Balance
Because cortisol touches so many systems, its regulation is tightly controlled by the brain through a tight feedback loop. When cortisol rises, it signals the hypothalamus and pituitary gland to reduce the release of hormones corticotropin-releasing hormone (CRH) and adrenocorticotropic hormone (ACTH) that stimulate further cortisol production. This feedback ensures that cortisol levels stay within a healthy range throughout the day.
Problems arise when this rhythm is disrupted. Chronically elevated cortisol, whether due to ongoing stress or disorders like Cushing’s syndrome, can lead to a range of health issues: abdominal weight gain, high blood pressure, insulin resistance, frequent infections, and mood disturbances. On the other hand, inadequate cortisol, as seen in Addison’s disease, can cause fatigue, low blood pressure, loss of appetite, and in some cases, life-threatening adrenal crises.
Fortunately, most people do not fall into these extremes. Generally, your focus should be on supporting the body’s natural cortisol rhythm. Simple practices like getting morning sunlight, maintaining regular sleep and wake times, managing stress, and eating balanced meals can go a long way toward promoting healthy cortisol patterns.
Cortisol is not the stress villain. It’s an essential hormone that helps us wake up, stay energized, think clearly, fight inflammation, and navigate physical or emotional stress. Problems occur when its rhythm is thrown off, not when it's doing its job.
Dr. Jonathan Moustakis
Co-Founder and CTO of Lume Health
References
O’Byrne NA, Yuen F, Butt WZ, Liu PY. Sleep and circadian regulation of cortisol: A short review. Curr Opin Endocrinol Metab Res. 2021;18:178–186. https://doi.org/10.1016/j.coemr.2021.03.011
Yang S, Zhang L. Glucocorticoids and vascular reactivity. Curr Vasc Pharmacol. 2004;2(1):1–12. https://doi.org/10.2174/1570161043476483
Reid IR. Glucocorticoid osteoporosis: mechanisms and management. Eur J Endocrinol. 1997;137(3):209–217. https://doi.org/10.1530/eje.0.1370209
Liggins GC. The role of cortisol in preparing the fetus for birth. Reprod Fertil Dev. 1994;6:141–150. https://doi.org/10.1071/RD9940141
