Forever Health

Introduction

For decades, health researchers and biohackers alike have pointed to a dramatic surge in cortisol — the body’s primary stress hormone — in the minutes after you wake up each morning. This phenomenon, dubbed the Cortisol Awakening Response (CAR), was believed to represent the body’s biological alarm system firing up for the day: a purposeful spike to mobilize energy, sharpen focus, and prime the immune system for the challenges ahead. Morning wellness routines across the world have been built around this idea.

But a landmark 2025 study published in Proceedings of the Royal Society B by researchers at the University of Bristol has thrown this long-held belief into serious doubt. Using cutting-edge in vivo microdialysis — a method that measures tissue-free cortisol with unprecedented precision — the team tracked cortisol levels in 201 healthy volunteers at home, before and after waking. Their striking null finding: the rate of cortisol secretion showed no significant increase in the hour after waking compared to the preceding hour of sleep.

If the cortisol awakening response isn’t driven by waking itself, what is actually happening in your body every morning — and what does this mean for your health? Here is what the latest science and leading experts have to say.

What the Experts Are Saying

Dr. Andrew Huberman, neuroscientist and host of the Huberman Lab podcast, has long emphasized that the morning cortisol surge is one of the most important biological events of your day. In his widely cited episode on cortisol and energy, Huberman explains: “Your highest levels of cortisol are first thing in the morning when you wake up. One way or another, every 24 hours, you will get an increase in cortisol. That is non-negotiable. That is written into your genome.” Critically, Huberman frames this morning cortisol peak as something to leverage — by getting bright light exposure within the first 30 minutes of waking, which his research suggests can amplify morning cortisol by as much as 50%, boosting immune function, alertness, and setting the body’s sleep timer for 14–16 hours later. Whether the spike is triggered by waking or pre-programmed by circadian biology, Huberman’s take is clear: the timing and magnitude of morning cortisol is something you can optimize.

Dr. Peter Attia, physician and longevity medicine specialist, tackles the cortisol story from the clinical endocrinology angle. In his landmark Episode 256, “The Endocrine System,” Attia walks through the HPA (hypothalamic-pituitary-adrenal) axis and makes a critical clinical point that most people miss: blood tests for total cortisol are largely useless for assessing adrenal function. The biologically active form is free cortisol, best measured through saliva or 24-hour urine collection across multiple time points in the day. This nuanced view of cortisol measurement aligns with the new 2025 research, which also emphasized the enormous variability between individuals in their cortisol dynamics — a variability that a single morning blood draw would completely fail to capture.

Dr. Robert Sapolsky, Stanford neuroendocrinologist and author of Why Zebras Don’t Get Ulcers, has for decades described cortisol’s dual nature: life-saving in short bursts, destructive when chronically elevated. His research highlights how long-duration cortisol exposure can damage hippocampal neurons, impair memory, and accelerate aging — making the question of what drives your morning cortisol pattern far from academic.

The Science Behind It

The 2025 University of Bristol study used microdialysis catheters to measure interstitial fluid cortisol — the free, biologically active form — in real time as participants naturally woke in their home environments. The key finding: cortisol was already rising robustly before awakening, driven by the body’s internal circadian clock. The suprachiasmatic nucleus (SCN) in the hypothalamus begins signaling the adrenal glands to ramp up cortisol production in the pre-dawn hours, typically around 3–4 AM, with levels naturally peaking close to the individual’s habitual wake time.

Sleep duration was a significant moderating variable: volunteers who slept approximately nine hours showed their cortisol peak before waking, while those sleeping around six hours peaked after waking — suggesting it’s not the act of waking but the relative timing of the circadian cortisol wave that matters. A 2025 review article in Neuroscience & Biobehavioral Reviews by Velazquez Sanchez and Dalley, titled “The Cortisol Awakening Response: Fact or Fiction?”, frames this as a “dual control” model: the CAR is shaped by both the circadian clock and neurocognitive anticipatory signals (like anxiety about the upcoming day), but does not appear to be directly triggered by the act of waking.

What this means practically: your morning cortisol pattern is primarily a function of your sleep schedule consistency, sleep duration, circadian alignment with light and darkness, and your baseline stress load — not simply whether you “wake up suddenly.”

Key Benefits

• Optimized morning energy without alarm anxiety: Since cortisol rises are circadian-driven, consistent wake times aligned with natural light dramatically improve morning alertness and reduce the grogginess associated with waking at the wrong circadian phase.
• Stronger immune priming: The morning cortisol peak plays a genuine role in mobilizing immune cells and managing inflammation for the day ahead — understanding its timing lets you strategically support it with morning sunlight exposure and appropriately timed exercise.
• Better HPA axis resilience: Knowing that chronic stress dysregulates the circadian cortisol curve — and not just raises absolute levels — gives practitioners a more targeted approach to testing and treating adrenal dysfunction using free cortisol patterns throughout the day.
• Reduced overdiagnosis of “adrenal fatigue”: With clearer science distinguishing circadian cortisol patterns from true adrenal insufficiency, clinicians and patients can move past vague concepts toward actionable saliva cortisol profiling.
• Personalized sleep optimization: The finding that sleep duration alters the timing of the cortisol peak has direct implications for matching sleep schedules to individual chronotype and activity demands.
• Smarter supplement and lifestyle timing: Tools known to modulate cortisol — including morning sunlight, cold exposure, ashwagandha, phosphatidylserine, and exercise timing — can now be deployed with greater precision based on where you are in your individual cortisol arc.

How to Get Started

The most powerful lever you have over your morning cortisol curve is sleep schedule consistency. Anchoring your wake time to the same hour every day — even on weekends — trains your circadian clock and ensures your cortisol peak aligns with your active period. Pair this with morning light exposure within the first 30 minutes of waking: even 5–10 minutes of outdoor daylight on a clear day, or 20–30 minutes on an overcast day, strengthens the circadian signal to the adrenals.

To get a real picture of your cortisol pattern, consider four-point salivary cortisol testing (morning, midday, afternoon, evening) rather than a single morning blood draw. This profile reveals whether your cortisol curve is too flat, too steep, or inverted — each pattern pointing to different root causes and interventions. Reduce unnecessary early-morning stressors where possible: checking email or social media immediately upon waking can trigger anticipatory cortisol spikes that compound the natural circadian rise. If you experience significant morning anxiety or “wired-but-tired” patterns, consider working with a functional medicine clinician trained in HPA axis assessment.

What to Watch Out For

While cortisol in appropriate morning amounts is beneficial, chronically elevated or chronically suppressed cortisol both carry significant health risks. Signs of cortisol dysregulation include persistent morning fatigue despite adequate sleep, difficulty falling asleep at night (indicating cortisol may be peaking at the wrong time), unexplained weight gain around the abdomen, immune suppression, brain fog, and mood instability.

Be cautious with supplements marketed as “cortisol blockers” — indiscriminate cortisol suppression can impair immune function and blood sugar regulation. Stimulant use (including high caffeine intake early in the morning) can artificially spike cortisol, shifting the curve and contributing to afternoon crashes. People with confirmed adrenal insufficiency (Addison’s disease) or Cushing’s syndrome require medical management and should never attempt to self-treat based on general wellness guidance. Always consult a qualified endocrinologist or physician before making significant interventions to your hormonal health.

Watch the Full Expert Videos

Andrew Huberman (Huberman Lab): Using Cortisol & Adrenaline to Boost Our Energy & Immune System — Huberman Lab Podcast #18

Peter Attia, M.D. (The Drive): The Endocrine System: Exploring Thyroid, Adrenal, and Sex Hormones — Episode #256

Andrew Huberman (Huberman Lab Essentials): Essentials: Boost Your Energy & Immune System with Cortisol & Adrenaline — Huberman Lab