Could Your Anxiety Be Coming from Your Body? 7 Root Causes Doctors Often Miss

Could Your Anxiety Be Coming from Your Body? 7 Root Causes Doctors Often Miss

You have tried therapy. Maybe medication. You have done the breathing, read the books, practiced the techniques. And the anxiety is still there — not budging in the way it should, or cycling back every time you think it has finally loosened its hold.

When that is the case, it is worth asking a different question. Not what psychological intervention haven’t I tried, but: is something in my body driving this that hasn’t been identified yet?

In my clinical practice, physiological contributors to anxiety are among the most commonly missed — and the most consistently undertreated — factors in people who have not responded fully to conventional care. They are not rare. They are simply not part of the standard anxiety evaluation.

What follows are seven of the most clinically significant ones. If any of them fit your pattern, that fit is information worth taking to a clinician.

The Seven Root Causes of Anxiety

1. Thyroid Dysfunction

Both hyperthyroidism and hypothyroidism can produce anxiety symptoms significant enough to receive a psychiatric diagnosis before the thyroid is ever evaluated. A 2023 case report published in Cureus documented a 33-year-old woman whose hyperthyroidism produced anxiety symptoms that led directly to a misdiagnosis of generalized anxiety disorder. A 2025 Cureus case report described a 32-year-old woman whose hypothyroidism produced anxiety-like symptoms for ten months before a thyroid panel was ordered — ten months during which she received treatment for a condition she did not have.

These cases are not anomalies. The thyroid governs the metabolic rate of virtually every system in the body, including the nervous system. When thyroid hormone is too high, the system is overdriven — producing palpitations, tremors, heat intolerance, weight loss, and anxiety that can be indistinguishable from a primary anxiety disorder. When it is too low, the metabolic slowdown can paradoxically produce anxiety through HPA axis compensation and neurotransmitter disruption.

A standard TSH alone is not sufficient to rule out thyroid contribution. A full panel — TSH, free T3, free T4, reverse T3, and thyroid antibodies — gives a complete picture. If your anxiety has not been evaluated with a full thyroid panel, that is the most important first step.

2. Gut Dysbiosis and the Gut-Brain Axis

The gut and brain communicate through a bidirectional highway — the gut-brain axis — involving the vagus nerve, the immune system, and a dense network of neurotransmitter-producing cells lining the gastrointestinal tract. The gut produces approximately 90 percent of the body’s serotonin. It also produces GABA, dopamine precursors, and a range of neuroactive metabolites that directly influence brain function and mood.

When the gut microbiome is disrupted — through antibiotic use, chronic stress, poor diet, or infection — that disruption translates upstream. A 2025 Frontiers review of microbiota-gut-brain axis research confirmed mechanistic links between dysbiosis and anxiety through vagal signaling, immune activation, and altered neurotransmitter production. Stanford Medicine’s 2025 analysis of gut-brain connection research described the gut as a “second brain” whose microbial composition has measurable effects on anxiety, stress reactivity, and mood regulation.

Gut anxiety — one of the nine types described in Panic Proof — often presents as anxiety that lives below the diaphragm: nausea before stressful situations, IBS that flares with emotional stress, a digestive system that seems to respond to the nervous system’s state before the mind registers it. When the gut is addressed, the anxiety often shifts in parallel.

Related: Anxiety and Panic: A Holistic Map to Understanding Your Symptoms →

3. Blood Sugar Dysregulation

Blood sugar fluctuation is one of the most underrecognized physiological drivers of anxiety — and one of the most correctable. When blood glucose drops, the body releases cortisol and adrenaline to compensate, producing a sympathetic activation state that is physiologically identical to anxiety: heart racing, shakiness, difficulty concentrating, a sense of unease or dread.

This pattern typically follows a meal timing rhythm: anxiety that arrives mid-morning, mid-afternoon, or in the early hours of the morning (when blood sugar naturally dips) is worth tracking against food intake. People who skip breakfast, eat high-carbohydrate meals without adequate protein and fat, or go long periods without eating are particularly susceptible to this pattern.

The clinical investigation is straightforward: fasting glucose, fasting insulin, and HbA1c provide a baseline picture. The intervention — stabilizing blood sugar through regular protein-rich meals and strategic snacking — can produce meaningful anxiety reduction without any other change.

For a deep dive into blood sugar and anxiety: Blood Sugar, Cortisol, and Anxiety: Why You Feel Fine Until You Crash →

4. Nutrient Deficiencies

Several micronutrients have well-established roles in nervous system regulation and anxiety resilience. Their deficiency — which is more common than is generally recognized, particularly in people under chronic stress — directly affects the neurochemical environment in which anxiety either escalates or resolves.

A 2025 PMC analysis using Mendelian randomization found causal protective roles for vitamin C, magnesium, and selenium against anxiety risk. A 2023 systematic review of randomized controlled trials concluded that B vitamin and vitamin D supplementation produced significant reductions in anxiety symptoms, with particular evidence for methylfolate, B12, and vitamin D as adjuvant interventions.

The nutrients most consistently relevant to anxiety include:

• Magnesium: supports GABA function, reduces HPA axis reactivity, promotes nervous system regulation. Deficiency is widespread — estimated at over 50% of the US population — partly because chronic stress depletes it faster than diet replenishes it.
• Vitamin D: acts as a neuroactive steroid, supports serotonin synthesis, and modulates immune and inflammatory pathways that affect mood. Low levels are extremely common, particularly in northern latitudes and in people who work indoors.
• B12 and methylfolate: essential for methylation, neurotransmitter synthesis, and myelin integrity. Deficiency can produce anxiety, depression, brain fog, and neuropathy — and is more common in people with certain genetic variants (MTHFR) that impair folate metabolism.
• Zinc: cofactor for GABA receptors and glutamate regulation. Deficiency shifts the neurochemical balance toward excitatory dominance.

Nutritional assessment — through serum levels and, where relevant, functional markers — is a standard component of a thorough integrative evaluation for anxiety.

5. HPA Axis Dysregulation (Chronic Stress Physiology)

The hypothalamic-pituitary-adrenal axis is the body’s primary stress response system. Under conditions of chronic or prolonged stress, it does not simply stay elevated — it dysregulates, producing patterns of abnormal cortisol timing, blunted awakening response, and altered sensitivity to feedback signals that maintain the cycle.

HPA axis dysregulation is not “adrenal fatigue” as that term is colloquially used — the adrenal glands are rarely actually fatigued. What is disrupted is the regulatory axis controlling their output. The result is a cortisol pattern that no longer follows the healthy diurnal curve, producing symptoms that include fatigue combined with hyperarousal, poor stress resilience, sleep disruption, and persistent low-grade anxiety that does not respond to standard treatment because the standard treatment is not addressing the hormonal pattern driving it.

Assessment requires a salivary or dried urine cortisol curve — typically collected at four points across the day — to map the actual rhythm. Treatment is individualized based on the pattern: some people need adrenal support, some need HPA axis regulation through adaptogenic botanicals, some need fundamentally different stress load management, and most need some combination of these.

6. Inflammatory and Immune System Activation

Inflammatory cytokines cross the blood-brain barrier and directly affect neurotransmitter metabolism, neuroplasticity, and mood regulation. This is not a hypothesis — it is a well-documented neuroinflammation pathway. Elevated inflammatory markers are found at increased rates in people with anxiety disorders, and conditions associated with systemic inflammation (autoimmune disease, chronic infection, mast cell activation, post-viral syndromes including long COVID) frequently produce anxiety as a neurological symptom.

Immune anxiety — another of the nine types from Panic Proof — should be considered when anxiety appeared or significantly worsened following an illness, when it co-occurs with unexplained physical symptoms, or when it has not responded to interventions that typically work. Basic inflammatory markers (CRP, homocysteine, ferritin) provide a starting point. More detailed immune investigation is warranted when the clinical picture suggests it.

7. Hormonal Fluctuation

Estrogen and progesterone have direct effects on GABA receptors, serotonin signaling, and HPA axis reactivity. When these hormones fluctuate — in the premenstrual phase, postpartum, or during the perimenopause transition — anxiety can emerge or intensify in ways that track closely with the hormonal cycle rather than with life circumstances.

Premenstrual anxiety that reliably appears in the luteal phase and resolves with menstruation is a hormonally driven pattern. Postpartum anxiety is a hormonally driven pattern. Perimenopause anxiety — particularly the onset of new anxiety symptoms in the mid-forties without an obvious psychological trigger — is a hormonally driven pattern. In all of these cases, treating the anxiety without evaluating the hormonal context produces incomplete results.

A full sex hormone panel — estrogen, progesterone, testosterone, DHEA, and FSH where relevant — provides the clinical picture. Treatment of hormonally driven anxiety that addresses the hormonal driver directly produces more complete and lasting resolution than psychological intervention alone.

KEY TAKEAWAYS
• Thyroid dysfunction — both hypo and hyper — can be misdiagnosed as generalized anxiety disorder; a full panel is essential
• Gut dysbiosis disrupts neurotransmitter production and vagal signaling in ways that directly drive anxiety symptoms
• Blood sugar dysregulation triggers cortisol and adrenaline release that is physiologically identical to anxiety
• Magnesium, vitamin D, B12, and zinc deficiencies directly impair the neurochemical environment required for anxiety resilience
• Hormonal fluctuation — premenstrual, postpartum, perimenopausal — is a primary driver of anxiety that is frequently undertreated
• Inflammatory and immune activation produce neuroinflammatory anxiety that does not respond to standard treatment

Why These Causes Get Missed

The standard psychiatric evaluation for anxiety does not typically include thyroid panels, cortisol curves, nutritional assessment, gut evaluation, or inflammatory markers. It assesses symptoms and history. If the symptoms meet criteria, the diagnosis is made and treatment begins — often with therapy, medication, or both.

This is not a failure of intention. It is a structural limitation: most clinical encounters do not have the time or the mandate to conduct the physiological investigation that root-cause anxiety care requires. A fifteen-minute primary care visit can refer to psychiatry; it cannot order and interpret a salivary cortisol curve, review a full thyroid panel in context, or discuss the clinical implications of a microbiome assessment.

The people who fall through this gap are not rare. They are the patients who have been through multiple therapeutic approaches, who respond partially but not fully, who cycle back to the same pattern despite consistent effort. If that description fits, a physiological evaluation is not a departure from evidence-based care. It is the next logical clinical step.

For the complete root-cause framework and what a holistic evaluation looks like: Anxiety and Panic: A Holistic Map to Understanding Your Symptoms →

For guidance on when physical symptoms warrant evaluation: When to Worry — Symptoms That Might Be More Than Anxiety →

Frequently Asked Questions

How do I know if my anxiety has a physical cause?

The most useful clinical indicators are: anxiety that began or significantly worsened after a physical event (illness, pregnancy, hormonal shift), anxiety that follows a predictable physiological rhythm (tied to meals, menstrual cycle, or time of day), anxiety that has not responded adequately to standard treatment, and anxiety accompanied by physical symptoms that haven’t been fully explained. Any of these patterns warrant a comprehensive physiological evaluation.

What labs should I ask for to evaluate physical causes of anxiety?

A thorough evaluation may include: full thyroid panel (TSH, free T3, free T4, reverse T3, thyroid antibodies); sex hormone panel (estrogen, progesterone, testosterone, DHEA, FSH); salivary or dried urine cortisol curve; fasting glucose, fasting insulin, HbA1c; inflammatory markers (CRP, homocysteine, ferritin); micronutrient assessment (magnesium, vitamin D, B12, zinc); and comprehensive metabolic panel. Not every person needs every panel — the clinical picture guides the investigation.

Can fixing a nutrient deficiency really reduce anxiety?

In people whose anxiety is being driven or amplified by a deficiency, yes — significantly. The evidence is strongest for magnesium, vitamin D, and B vitamins. A 2025 PMC analysis using Mendelian randomization found causal protective roles for magnesium, vitamin C, and selenium against anxiety risk. A 2023 systematic review of RCTs found that B vitamin and vitamin D supplementation produced significant anxiety reductions. These are not general wellness interventions — they are targeted corrections for a measurable physiological deficit.

What is the gut-brain axis and how does it affect anxiety?

The gut-brain axis is the bidirectional communication network between the gastrointestinal tract and the central nervous system, operating through the vagus nerve, the immune system, and neurotransmitter-producing cells in the gut lining. The gut produces approximately 90% of the body’s serotonin and contributes to GABA and dopamine production. When the gut microbiome is disrupted — through stress, infection, antibiotics, or poor diet — that disruption affects brain function and anxiety directly through multiple simultaneous pathways.

Can hormonal changes cause anxiety even if I’ve never had anxiety before?

Yes — and this is one of the most underrecognized presentations in clinical practice. New-onset anxiety in the premenstrual phase, postpartum period, or perimenopause is frequently hormonally driven. Progesterone is GABAergic — it directly supports the calming neurotransmitter system — and its decline in the luteal phase and perimenopausal transition directly affects anxiety thresholds. Many people experience their first significant anxiety episode during these windows without any change in life circumstances. Hormonal evaluation is essential in these cases.

Your Next Step

If any of these seven causes resonated — if you recognized your pattern in the thyroid section, the hormonal section, or the blood sugar section — that recognition is worth acting on.

The 9 Types of Anxiety Quiz is a useful starting map for identifying which physiological and psychological systems are most active in your particular pattern. It takes a few minutes and is free.

Take the Free 9 Types of Anxiety Quiz →

For the complete clinical framework — the nine-type model, the root-cause investigation protocol, and the step-by-step approach to addressing anxiety at its source — Panic Proof covers the full picture.

Learn more about Panic Proof →

About Dr. Nicole Cain

Dr. Nicole Cain, ND, MA, is a licensed Naturopathic Physician and EMDR-trained clinical psychotherapist specializing in anxiety, panic disorder, and trauma. She is the author of Panic Proof: The New Holistic Solution to End Your Anxiety (Rodale, 2024). Her clinical practice integrates root-cause medicine with nervous system-focused care to address anxiety at its source rather than managing it at the surface.

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