The Liver, Bile, and the Brain Adrenal (HPA) Axis
By Dr. Fiona McCulloch, ND: A functional endocrinology perspective on the connections between liver function, bile acids, cortisol regulation, and perimenopause symptoms.
If you’ve noticed that the standard explanation for hot flashes, declining estrogen, doesn’t fully account for what you’re experiencing, you’re noticing something clinically significant. Estrogen decline doesn’t explain why hot flashes strike at 3am but not midnight, why a stressful week makes them dramatically worse, or why some nights are catastrophic and others are manageable. It also doesn’t explain why perimenopause insomnia can resist every sleep hygiene strategy you’ve tried.
Many women in perimenopause recognize these patterns but are told the answer is simply “your estrogen is dropping.” That’s true, but it’s incomplete. The missing variable is the HPA axis, and the liver-bile system that influences it. This page explains the mechanism behind these patterns. It does not cover treatment protocols: those are addressed on dedicated pages for hot flashes, insomnia, and PCOS. If you’re looking for an overview of our approach to this stage of life, see the perimenopause and menopause program.
What Is the HPA Axis?
The HPA axis, the hypothalamic-pituitary-adrenal axis, is the brain’s central stress response system. When your brain registers a stressor, the hypothalamus signals the pituitary gland, which in turn signals the adrenal glands (located above the kidneys) to release cortisol. Cortisol helps the body manage stress by regulating energy release, immune function, and metabolism.
Cortisol follows a circadian rhythm. In a healthy pattern, levels rise in the early morning to help you wake and feel alert, then gradually decline through the day, reaching their lowest point at night to allow sleep. When this rhythm is disrupted, cortisol staying elevated at night, or failing to rise in the morning, the downstream effects include the symptoms many women experience in perimenopause: hot flashes with specific timing patterns, middle-of-the-night waking, and insomnia that doesn’t respond to conventional sleep advice.
Bile Acids Are Endocrine Signaling Molecules
Most people think of bile as a digestive fluid, something the liver produces and the gallbladder stores to help break down fats. This is true, but it understates what bile acids actually do. Research has established that bile acids function as endocrine signaling molecules, activating receptors (including FXR and TGR5) that regulate glucose metabolism, lipid metabolism, energy expenditure, and, critically, cortisol regulation.
Bile acids have been found to directly affect the hypothalamus and its communication with the adrenal glands. In a healthy system, bile acids are secreted into the gallbladder, excreted through the intestines, and recycled back to the liver in a cycle that maintains homeostasis. When this cycle is disrupted, bile acids can escape into the bloodstream, cross the blood-brain barrier, and activate cortisol receptors in the brain, suppressing the natural production of cortisol in response to both stress and circadian rhythm. This is how the liver connects to the brain’s stress response system: not through “detoxification” in the wellness-marketing sense, but through measurable endocrine signaling pathways. For more on how bile acids interact with hormonal health in PCOS, see bile acids and PCOS.
Cholestasis: When Bile Flow Slows Down
Cholestasis (reduced bile flow from the liver and gallbladder into the intestine) impairs this bile acid signaling cycle. When bile flow slows, toxic bile components can accumulate in the liver, and the endocrine signaling that bile acids normally perform is disrupted. The effects extend beyond digestion: impaired bile acid circulation means impaired cortisol regulation, which means impaired HPA axis function.
Risk factors associated with cholestasis include:
- Polycystic ovary syndrome (PCOS)
- Insulin resistance and prediabetes
- Fatty liver disease (NAFLD)
- Pregnancy and the postpartum period
Symptoms that may indicate sluggish bile flow include difficulty digesting fats, nausea or heaviness after eating, fatigue, and a history of gallbladder issues. These are common presentations that many women dismiss as unrelated to their hormonal symptoms, but the bile acid signaling connection means they may not be unrelated at all.
The liver’s role extends beyond bile production. It controls cholesterol availability for hormone synthesis, and HDL cholesterol is the preferred substrate the adrenals use for cortisol production. It manages energy distribution throughout the body. It processes and clears cortisol. When liver function is compromised by fatty liver disease or cholestasis, the downstream effect on cortisol regulation creates a mechanism that connects directly to the perimenopause symptoms explored in the following sections.
Why Hot Flashes Happen at 3am: The HPA Axis Connection
The standard explanation for hot flashes in perimenopause focuses on declining estrogen and its effect on the brain’s thermoregulatory center. This is accurate; estrogen decline alone does not explain timing patterns: why hot flashes happen at certain hours, why stress makes them markedly worse, or why severity varies dramatically from night to night. The variable that explains these patterns is the HPA axis.
Cortisol and corticotropin-releasing hormone (CRH) influence the same hypothalamic regions that regulate body temperature. Elevated nocturnal cortisol is associated with increased hot flash frequency and severity. Norepinephrine, released as part of the stress response, further narrows the thermoneutral zone. The circadian pattern, nocturnal hot flashes coinciding with cortisol dynamics, implicates HPA axis function as a modulating mechanism alongside, not instead of, estrogen decline.
In clinical practice, Dr. McCulloch observes specific cortisol patterns in women whose hot flashes have HPA-mediated characteristics. Some patients show high cortisol at night with a flattened morning pattern: cortisol that should be low during sleep remains elevated, and the morning rise that should signal wakefulness is blunted. In the middle of the night, core body temperature naturally rises; when this combines with elevated cortisol, the compound effect can trigger hot flashes.
Other patients present with a very reactive adrenal axis: women who have experienced significant or sustained stress may find that even small or moderate stressors produce outsized cortisol responses. These patients sometimes show a very high morning cortisol peak or unexpected afternoon cortisol spikes when assessed with a 4-point cortisol panel. A morning blood cortisol test can reveal whether the brain-adrenal feedback loop tied to circadian rhythm is functioning normally, or whether the signaling between the hypothalamus and the adrenals has been altered.
The clinical significance is this: if hot flashes are partly driven by cortisol pattern disruption, then understanding cortisol dynamics adds information that estrogen-focused management alone may not capture. This is not a replacement for hormonal evaluation; it is an additional dimension that, for some women, explains what estrogen decline alone does not. For more on the estrogen and cortisol relationship, see the dedicated page.
If hot flashes are your primary concern, our dedicated page on naturopathic approaches to hot flashes in perimenopause covers the assessment and management options available, including the HPA axis dimension discussed here.
Perimenopause Insomnia: Why It's Not "Just Stress"
If you’ve been told that your perimenopause insomnia is “just stress”, or conversely, “just hormones”, neither explanation captures the full picture. Perimenopause insomnia typically involves two concurrent mechanisms, and understanding both is necessary to understand why sleep has changed so fundamentally.
Pathway 1: Cortisol-HPA Axis
Elevated nocturnal cortisol disrupts sleep architecture, driving middle-of-the-night waking. Core body temperature rises in the second half of the night, and when cortisol remains elevated, this compounds the arousal signal. As estrogen’s modulatory effect on cortisol declines during perimenopause, cortisol may stay elevated for longer periods during sleep. This pathway explains the pattern many women describe: falling asleep is possible, but staying asleep is not, and waking at 2 or 3am becomes the norm.
Pathway 2: Progesterone-GABA
Progesterone decline during perimenopause means reduced production of allopregnanolone, a neurosteroid that activates GABA-A receptors and supports both sleep onset and slow-wave (deep) sleep. When progesterone production decreases, as it does when ovulation becomes irregular, the neurochemical support for sleep is diminished. This pathway explains difficulty falling asleep and the loss of restorative deep sleep. For a deeper exploration of this mechanism, see progesterone, allopregnanolone, and sleep in perimenopause.
Most perimenopause insomnia involves both pathways simultaneously. The cortisol pathway drives nocturnal arousal; the progesterone pathway removes the neurochemical support for returning to sleep. This is why sleep hygiene alone often falls short; it doesn’t address either underlying mechanism.
Dr. McCulloch approaches insomnia assessment individually. When a patient has a history of significant stress, demanding work, or trauma, she will almost always evaluate the HPA-cortisol pathway, because patients with sustained stress histories will typically show disruption in this system unless they have an exceptionally robust stress axis. When a patient reports PMS symptoms, cycle-related insomnia, or worsening sleep in the luteal phase, the progesterone pathway is more likely to be the primary contributor. In perimenopause, there may be no progesterone production at all; ovulation has simply stopped, and with it, the body’s primary source of this sleep-supporting hormone.
Both pathways can be assessed and addressed. For patients who prefer alternatives to progesterone, approaches involving pregnenolone, GABA support, or other strategies can be explored. The key insight is that perimenopause sleep symptoms are complex: hormone fluctuations affect cortisol, progesterone deficit affects GABA, and estrogen changes affect brain function and structure. Individual assessment determines which pathway is primary, which is secondary, and whether both need attention.
For women with PCOS, this two-pathway model is especially relevant. PCOS is associated with chronically reduced ovulation and follicular inflammation, both of which decrease progesterone production. Women with PCOS may enter perimenopause with less GABAergic sleep support than non-PCOS women, making the combined cortisol and progesterone disruption more pronounced.
For a deeper look at the progesterone-allopregnanolone-GABA pathway and how it relates to perimenopause sleep, see progesterone, allopregnanolone, and sleep in perimenopause.
PCOS, Fatty Liver, and Perimenopause: Why This Connection Matters
Non-alcoholic fatty liver disease (NAFLD) is significantly more prevalent in women with PCOS (estimates range from 34% to 70%), driven by insulin resistance, hyperandrogenism, and visceral adiposity (which can occur independently of BMI). During perimenopause, the loss of estrogen’s hepatoprotective effects independently increases fatty liver risk. For women with PCOS entering perimenopause, these two risk pathways compound.
The connection to the liver-bile-HPA axis mechanism discussed on this page is direct: fatty liver disease disrupts bile acid-FXR signaling, which disrupts cortisol regulation. Insulin resistance, common in PCOS and increasingly common in perimenopause, is linked to increased free cortisol production. In clinical practice, Dr. McCulloch observes that most patients with insulin resistance have elevated cortisol levels with patterns that are often not normal. The cortisol disruption then compounds the metabolic burden, creating a feedback loop.
A key clinical observation: during perimenopause, many women without PCOS develop insulin resistance as protective hormone production declines. In Dr. McCulloch’s clinical experience, non-PCOS perimenopause patients often become metabolically similar to PCOS patients, developing insulin resistance without the protective factors of normal hormone production. This means the fatty liver-bile-HPA mechanism is relevant not only for women with a PCOS diagnosis, but for any woman experiencing metabolic changes during perimenopause. For more on the adrenal dimension of PCOS, see adrenal androgen excess in PCOS.
At White Lotus Clinic, screening for fatty liver is part of comprehensive PCOS assessment. Dr. McCulloch screens every PCOS patient using:
- ALT liver enzymes
- Lipid panel and cholesterol
- Triglycerides
- CRP (inflammatory marker)
- Visceral fat and body composition assessment
- Referral for liver and fibrosis ultrasound where clinically indicated
Patients with fatty liver frequently present with high lipids, elevated triglycerides, elevated CRP, and weight gain concentrated around the midsection. These markers, combined with clinical history, provide a clear picture of whether the bile-liver-HPA mechanism is clinically relevant.
The most important thing to understand about fatty liver in PCOS: it is often reversible. The liver has a remarkable capacity for recovery. Unless fibrosis has developed, meaningful improvement is achievable for most patients when the contributing factors, particularly insulin resistance, are addressed. As Dr. McCulloch notes, education about this connection is integrated into ongoing PCOS care, and patients consistently find it empowering to learn that this aspect of their metabolic health can improve.
For a comprehensive look at naturopathic assessment for PCOS, including metabolic, hormonal, and adrenal factors, see naturopathic care for PCOS.
Two Things Social Media Gets Wrong About Cortisol
"Exercise Is Raising My Cortisol"
You may have seen content on TikTok or Instagram suggesting that exercise, especially intense exercise, is raising your cortisol and making your perimenopause symptoms worse. This is one of the most common misconceptions Dr. McCulloch corrects in consultations. Cortisol does rise during exercise, but that is part of how exercise works and how we recover from it. It is actually rare for exercise to be a clinical problem. True over-exercise exists, but for the vast majority of patients, exercise is not why cortisol patterns are disrupted. The concern is that this misconception can lead women to reduce physical activity, which is actually protective for metabolic health, including the insulin resistance that contributes to fatty liver risk.
"I Just Need to Lower My Cortisol"
The belief that cortisol is inherently bad and should always be lowered is the other major misconception patients bring into consultations. Many women have been looking for something, a supplement, a practice, a protocol, to lower their cortisol, believing that will resolve their perimenopause symptoms. But perimenopause sleep and vasomotor symptoms are more complex than a single hormone. Hormone fluctuations affect cortisol. Progesterone deficit affects GABA-mediated sleep support. Estrogen changes affect brain function and structure. Lowering cortisol alone does not address this complexity. As Dr. McCulloch observes, perimenopause sleep symptoms are actually quite complex, and individual assessment determines which mechanisms are most relevant for each patient. It is never just as simple as looking at the adrenals and cortisol.
What a Naturopathic HPA Axis Assessment Involves
Understanding the mechanism is valuable, but you may be wondering what a clinical evaluation of the HPA axis actually looks like. The difference between this assessment and generic “reduce your stress” advice is specificity: identifying particular cortisol patterns that reveal particular clinical information. Here is what the process involves at White Lotus Clinic:
- Clinical history review: stress patterns, sleep history, symptom timeline, menstrual cycle history (if applicable), PCOS status, and metabolic history. This establishes context for interpreting lab results and determines which pathways are most likely relevant.
- 4-point cortisol panel: salivary cortisol measured at four points across the day. This is the primary tool for identifying specific patterns: high nighttime cortisol, flattened morning rise, or reactive afternoon spikes that indicate a sensitized adrenal axis. Each pattern has different clinical implications.
- Morning blood cortisol: evaluates whether the brain-adrenal feedback loop tied to circadian rhythm is functioning normally. This shows whether the morning cortisol rise, the signal that connects the hypothalamus, the pituitary, and the adrenals, is intact.
- Metabolic and liver panels: ALT, lipids, triglycerides, CRP, fasting glucose and insulin. These screen for the metabolic dimension: fatty liver risk, insulin resistance, and the metabolic factors that affect bile acid signaling and cortisol regulation.
- Individual assessment: based on results and clinical presentation, the assessment determines whether to focus on the cortisol-HPA pathway, the progesterone pathway, or both. This is not a one-size-fits-all protocol. For more on cortisol testing and HPA axis assessment, see the dedicated page.
The difference between this assessment and generic “reduce your stress” advice: specific cortisol patterns reveal specific clinical information that informs specific management decisions. A flattened morning cortisol pattern has different implications than a reactive afternoon spike. A high-nighttime-cortisol pattern in someone with significant stress history calls for a different approach than cycle-related insomnia in someone with declining progesterone.
After assessment, patients understand which cortisol pattern they have, whether the HPA-cortisol pathway or the progesterone pathway (or both) is most relevant to their sleep or hot flash presentation, and what their metabolic markers indicate about liver function and insulin resistance. This transforms the mechanism explanation on this page from educational to personally relevant; it becomes information about your own physiology, not an abstract concept.
Frequently Asked Questions
What is the HPA axis and how does it relate to hot flashes?
The HPA (hypothalamic-pituitary-adrenal) axis is the brain’s stress response system. It regulates cortisol production in a daily circadian rhythm. When cortisol patterns are disrupted, particularly elevated nocturnal cortisol, this affects the hypothalamic regions that also regulate body temperature. In perimenopause, estrogen decline narrows the thermoneutral zone; HPA axis dynamics determine when and how severely hot flashes occur. Understanding the HPA dimension does not replace hormonal evaluation; it adds information that can help guide clinical decisions.
Can bile acid problems cause hormonal symptoms?
Bile acids are now understood to function as endocrine signaling molecules, not just digestive aids. They activate receptors (FXR, TGR5) that regulate glucose metabolism, lipid metabolism, and cortisol regulation. When bile acid signaling is disrupted, through cholestasis, fatty liver, or metabolic conditions, the downstream effects on cortisol and HPA axis function can contribute to hormonal symptoms. This is evidence-based physiology, not alternative medicine. Functional endocrinology, the discipline Dr. McCulloch trained in through her FABNE fellowship, studies these hormone-system interactions.
Why do hot flashes happen at night?
Several factors converge during sleep. Core body temperature naturally rises in the middle of the night. Cortisol dynamics shift during nocturnal hours. When cortisol remains elevated at night, a pattern Dr. McCulloch identifies through 4-point cortisol panels, this can compound with the natural core temperature rise to trigger hot flashes. The circadian pattern of nocturnal hot flashes implicates HPA axis function alongside the estrogen decline that narrows the thermoneutral zone.
What is the connection between cortisol and insomnia during perimenopause?
Perimenopause insomnia typically involves two concurrent pathways. The cortisol-HPA pathway drives nocturnal arousal: elevated cortisol disrupts sleep architecture and causes middle-of-the-night waking. The progesterone-GABA pathway involves the loss of sleep-supporting neurosteroids as ovulation declines. A naturopathic assessment can evaluate cortisol patterns to determine which pathway is most relevant for your presentation. This is different from generic stress-reduction advice because it identifies specific, measurable patterns that inform specific clinical decisions.
Does PCOS increase fatty liver risk during menopause?
Yes, NAFLD prevalence is significantly elevated in women with PCOS, driven by insulin resistance, hyperandrogenism, and visceral adiposity. This risk may compound during perimenopause as estrogen’s hepatoprotective effects decline. Importantly, fatty liver associated with PCOS is often reversible when contributing factors are addressed, particularly insulin resistance. Screening at White Lotus Clinic includes ALT liver enzymes, lipid panels, triglycerides, CRP, and referral for ultrasound where indicated. Proactive assessment enables early intervention, before fibrosis develops.
Does exercise cause cortisol problems?
This is a common concern driven by social media content, but exercise rarely causes clinical cortisol problems. Cortisol rises during exercise as part of the recovery process; this is normal and beneficial. True over-exercise is rare. As Dr. McCulloch notes, the belief that exercise harms cortisol can lead to avoidance of physical activity, which is actually important for metabolic health, including the insulin resistance that contributes to fatty liver risk and HPA axis disruption.
How does a naturopath assess HPA axis function?
Assessment includes a 4-point cortisol panel (salivary cortisol at four timepoints across the day), morning blood cortisol (evaluating the brain-adrenal circadian feedback loop), and metabolic panels (ALT, lipids, triglycerides, CRP, fasting glucose and insulin). Ontario naturopathic doctors can order and interpret these tests. Dr. McCulloch’s FABNE fellowship provides additional training in functional endocrinology, the discipline that studies HPA axis dynamics, cortisol patterns, and liver-bile-hormonal interactions. Cortisol pattern identification informs management because it reveals which mechanism is driving symptoms.
About Dr Fiona McCulloch, ND
- relevant to HPA axis assessment, cortisol patterns, and liver-bile metabolism
- Published author: 8 Steps to Reverse Your PCOS
- 2023 International PCOS Guidelines: peer reviewer
- Clinical focus: perimenopause, PCOS, and functional endocrinology (approximately 25 years of clinical experience)
- Medical director of White Lotus Clinic’s Menopause Program
- Fellow of the American Board of Naturopathic Endocrinology: functional endocrinology training directly
Understanding the Mechanism Is the First Step
Hot Flashes
If hot flashes are your primary concern, learn how naturopathic assessment approaches the HPA axis dimension alongside hormonal evaluation.
Insomnia
PCOS & Metabolic Health
If hot flashes are your primary concern, learn how naturopathic assessment approaches the HPA axis dimension alongside hormonal evaluation.
To discuss your symptoms with a practitioner who understands the liver-bile-HPA axis connection, a consultation through our perimenopause and menopause program is a starting point. If symptoms are affecting your daily life, a consultation can help clarify your options.