Your Anxiety Might Not Be Mental. These Physical Causes Get Missed
You've sat in therapy. You've tried breathing exercises. You've been told it's "all in your head." You've maybe tried antidepressants, which either didn't help or made you feel worse. And you're still living with racing thoughts, chest tightness, that constant sense of dread, or the sudden panic attacks that come from nowhere.
Here's what most mental health professionals won't tell you, because it's outside their training: your anxiety might not be primarily psychological. It might be physical. Your body might be screaming at you through symptoms you've been taught to interpret as pure anxiety, when actually something metabolic, hormonal, nutritional, or inflammatory is happening underneath.
This isn't controversial. The research is consistent. The problem is that anxiety gets branded as a psychological condition, so nobody runs the blood tests that would reveal the actual cause.
Thyroid dysfunction mimicking anxiety, especially the subtle kind
One of the most common physical causes of anxiety that gets overlooked is thyroid dysfunction. Not the obvious hypothyroidism with weight gain and fatigue. I'm talking about subclinical hyperthyroidism, the kind where your TSH is technically "in range" but your free T3 and free T4 are elevated, or where you have antibodies against your thyroid without full-blown Hashimoto's.
When your thyroid is overactive, even slightly, your metabolic rate increases. Your nervous system becomes sensitised. You experience racing thoughts, restlessness, heart palpitations, and that constant sense of being on edge. It's biochemically identical to anxiety, because it is anxiety. Your body is in a hypermetabolic state.
A 2021 review in Thyroid journal analysed multiple studies and found that subclinical hyperthyroidism was significantly associated with anxiety symptoms, even when TSH was still in the "normal range." The mechanism is straightforward: excess thyroid hormone increases beta-adrenergic receptor sensitivity, making you hyperresponsive to adrenaline.
The problem: most GPs only test TSH. TSH can be normal while free T3 and free T4 are elevated. Or they test it once and don't investigate why your thyroid is overactive in the first place. Hashimoto's disease, for example, causes autoimmune attacks on your thyroid that can swing between hypothyroid and hyperthyroid phases.
What to do: Ask your GP for a full thyroid panel: TSH, free T4, free T3, TPO antibodies, and thyroglobulin antibodies. If your GP refuses or says TSH is enough, go private. A comprehensive thyroid assessment costs under 100 pounds and can completely reframe your anxiety.
Blood sugar dysregulation and panic-like symptoms
When your blood sugar crashes, your body releases adrenaline to bring it back up. Adrenaline is the fight-or-flight hormone. It causes your heart to race, your muscles to tense, your mind to sharpen and race. It feels exactly like panic.
For people with reactive hypoglycemia (blood sugar that drops too quickly after meals), this can happen multiple times a day. You eat a sugary food or a high-carb meal on an empty stomach, your blood sugar spikes, your pancreas overcompensates with insulin, your blood sugar crashes 2-3 hours later, adrenaline floods your system, and you feel like you're having a panic attack. Except it's not psychological. It's metabolic.
A 2015 study published in Appetite found that people with reactive hypoglycemia reported significantly higher anxiety scores, and that blood glucose stability correlated directly with anxiety reduction. When they stabilised their blood sugar through dietary changes, their anxiety improved without any psychological intervention.
The classic presentation: you feel fine in the morning, energy crashes mid-afternoon or 2-3 hours after lunch, you feel shaky and anxious, you reach for something sweet, feel briefly better, then crash again an hour later. This is reactive hypoglycemia, not anxiety disorder.
What to do: Ask for a fasting glucose test, but more importantly, ask for a fasting insulin test and ideally a glucose tolerance test. Many people have normal fasting glucose but dramatically elevated fasting insulin, which means they're in a pre-diabetic state and experiencing constant blood sugar dysregulation. Track your blood sugar patterns if you have access to a continuous glucose monitor, even a basic one. You'll see exactly when and how much your blood sugar drops.
B12 deficiency and the psychiatric symptoms nobody connects
Vitamin B12 is critical for nervous system function. Deficiency causes neurological and psychiatric symptoms that are often misdiagnosed as anxiety, depression, or even psychosis before the actual deficiency is caught.
A 2010 review in Psychiatric Times examined the psychiatric manifestations of B12 deficiency and found that anxiety, panic attacks, depression, cognitive dysfunction, and even psychosis could be the presenting symptoms, appearing sometimes years before anaemia or other classic signs of deficiency showed up.
Who's at risk? Vegetarians and vegans are obvious, since B12 is primarily found in animal products. But also: anyone over 50 (stomach acid production declines), people taking metformin or proton pump inhibitors (which block B12 absorption), people with gut conditions like Crohn's or coeliac disease (which impair absorption), and anyone with pernicious anaemia, an autoimmune condition affecting B12 absorption.
The problem: standard blood tests often miss B12 deficiency. Your serum B12 might be in the "normal range" even when you're functionally deficient. Better markers are homocysteine and methylmalonic acid levels, which rise when B12 is inadequate at the cellular level.
What to do: Get your B12 level tested, but also ask for homocysteine and methylmalonic acid. If you're vegetarian, vegan, over 50, or on medications that affect absorption, consider supplementing with B12 regardless, particularly if you have anxiety symptoms. Sublingual or intramuscular B12 is more reliably absorbed than oral, especially if you have digestive issues.
Iron deficiency and the restlessness you can't explain
Iron is essential for oxygen transport to your nervous system. When you're iron deficient, your brain doesn't get enough oxygen. Your body responds with restlessness, anxiety, insomnia, and an uncomfortable urge to move your legs. Many people with iron deficiency get diagnosed with "generalised anxiety" or "restless leg syndrome" when they actually just need iron.
A 2020 systematic review published in Lancet Psychiatry analysed multiple studies and found that iron deficiency was significantly more common in people with anxiety disorders compared to controls. The mechanism is partly neurochemical: iron is required to produce serotonin and dopamine, the neurotransmitters that regulate mood and anxiety.
Who's at risk? Women of reproductive age due to menstrual blood loss. Vegans and vegetarians (plant-based iron is less bioavailable). People with digestive issues like coeliac disease. People taking certain medications. And anyone who hasn't had their iron properly tested.
The catch: ferritin (the standard iron test) can be elevated by inflammation, so it's unreliable. Serum iron and transferrin saturation are better, but the gold standard is looking at your complete iron panel: serum iron, ferritin, transferrin saturation, and TIBC (total iron binding capacity).
What to do: Ask for a complete iron panel, not just ferritin. If you're deficient, supplement with iron bisglycinate (better absorbed and less side effects than ferrous sulphate) along with vitamin C for absorption. Retest after 8-12 weeks. If you have significant anxiety and you're iron deficient, addressing the iron alone often dramatically improves your mental state.
Magnesium deficiency and the muscle tension you can't relax
Magnesium is involved in over 300 enzymatic reactions in your body, and it's one of the most common deficiencies in developed countries. It's critical for nerve function, muscle relaxation, and anxiety regulation. When you're deficient, your nervous system stays in a state of heightened alert.
The symptoms: muscle tension, jaw clenching, difficulty relaxing, racing thoughts, insomnia, and a constant sense of being wound up. These feel like anxiety, so they get treated as anxiety. But they're often just magnesium deficiency.
A 2017 meta-analysis in Nutrients by Boyle and colleagues reviewed multiple studies on magnesium and anxiety, finding consistent evidence that magnesium supplementation reduced anxiety symptoms. The effect was modest but significant, and magnesium was particularly effective for people with combined anxiety and muscle tension.
The problem: serum magnesium is unreliable. Your body tightly controls serum magnesium even when your cellular magnesium is depleted, because magnesium is crucial for cardiac function. A better test is red blood cell (RBC) magnesium, which reflects intracellular magnesium more accurately.
What to do: Ask for RBC magnesium, not serum magnesium. If you're deficient or even low-normal, supplement with magnesium glycinate (most absorbable and doesn't have a laxative effect like other forms). Start with 200-300mg daily and increase gradually. Many people notice improved anxiety and sleep within 2-3 weeks.
The gut-brain axis: where 95% of your serotonin actually lives
Your gut produces about 95% of your body's serotonin. Your gut bacteria directly communicate with your brain through the vagus nerve, the longest nerve in your body, running from your brain down to your intestines. This is called the gut-brain axis, and when your gut is inflamed or your bacterial balance is disrupted, it directly impacts your anxiety and mood.
When your gut lining is compromised (increased intestinal permeability, sometimes called "leaky gut"), inflammatory molecules enter your bloodstream. Your immune system activates. Inflammatory cytokines like TNF-alpha, IL-6, and IL-8 are released, which cross the blood-brain barrier and directly affect neurotransmitter balance. The result: anxiety, depression, brain fog, and mood instability that has nothing to do with your psychology and everything to do with your intestinal inflammation.
Research consistently shows that people with anxiety disorders have significantly different gut bacterial profiles compared to people without anxiety. This isn't causation proving causation, but multiple intervention studies show that improving gut health through diet, probiotics, and addressing dysbiosis reduces anxiety symptoms.
A 2019 review in Psychiatry Research examined probiotics and anxiety, finding that certain strains, particularly Lactobacillus and Bifidobacterium species, showed measurable reductions in anxiety when taken for 4-8 weeks. These are sometimes called psychobiotics.
What to do: If you have anxiety and any digestive symptoms (bloating, gas, irregular bowel movements, food sensitivities, constipation, diarrhoea), get a comprehensive stool test. Look for dysbiosis (imbalanced bacteria), inflammatory markers, and digestive function. Support your gut with increased fibre, reduced sugar and processed food, and consider targeted probiotics. The improvement in anxiety from gut healing alone can be dramatic.
Inflammatory markers and the anxiety-inflammation connection
Here's something that psychiatrists don't typically measure: inflammatory markers like CRP (C-reactive protein) and IL-6 (interleukin-6). But neuroscientists and researchers increasingly recognise that elevated inflammation is associated with anxiety and depression.
A landmark 2013 study by Vogelzangs and colleagues published in Archives of General Psychiatry found that people with elevated inflammatory markers had significantly higher rates of anxiety disorders. The relationship was dose-dependent: higher inflammation, higher anxiety. This wasn't just correlation; inflammation was predictive of who would develop anxiety over time.
What causes this inflammation? Dietary factors (processed food, refined sugars, low omega-3 intake), chronic stress, poor sleep, infections, autoimmune conditions, and gut dysbiosis all contribute. The point is: your anxiety might be a symptom of systemic inflammation, not a primary anxiety disorder.
What to do: Ask for high-sensitivity CRP (hs-CRP) and ideally IL-6. If you're inflamed, the priority is identifying and addressing the cause. Is it your diet? Your sleep? A chronic infection? Gut dysbiosis? Once you address the inflammation, anxiety often improves significantly. An anti-inflammatory diet, omega-3 supplementation, adequate sleep, and stress management are foundational.
Histamine intolerance and the anxiety you never see mentioned
Histamine is a neurochemical that regulates sleep-wake cycles, stress response, and mood. Some people have difficulty breaking down dietary histamine (due to low DAO enzyme activity), or they have conditions like mast cell activation syndrome where histamine is released excessively. The result: anxiety, panic, insomnia, and a host of other symptoms.
Foods high in histamine include aged cheeses, processed meats, fermented foods, some fish, tomatoes, and alcohol. If you have histamine intolerance, eating these foods causes immediate anxiety, heart palpitations, and restlessness. This is completely physical and has nothing to do with your psychological relationship to food or stress.
A 2021 review in Nutrients examined histamine intolerance and neuropsychiatric symptoms, finding consistent associations between elevated histamine and anxiety, panic, and mood disorders. Many people with anxiety have been on psychiatric treatment for years when they actually just needed a low-histamine diet.
What to do: Try a low-histamine elimination diet for 4 weeks. Remove aged cheeses, processed meats, fermented foods, fish (except very fresh), tomatoes, avocados, spinach, and alcohol. If your anxiety improves significantly, you've found your culprit. You can then work with someone to identify your specific triggers and potentially address the underlying cause (low DAO, mast cell activation, etc.).
Caffeine and cortisol: the amplifier you're using daily
Caffeine blocks adenosine receptors in your brain, preventing the signal that tells you you're tired. But more importantly, it stimulates adrenaline and cortisol release. For someone with underlying anxiety, whether from thyroid dysfunction, blood sugar dysregulation, or any other physical cause, caffeine doesn't just amplify the anxiety, it can create anxiety that wasn't there before.
Some people are fast caffeine metabolisers and can handle it fine. Others are slow metabolisers, particularly those with certain genetic variations. For a slow metaboliser consuming multiple cups of coffee daily, they're essentially living in a state of chronic adrenaline stimulation. It feels like anxiety. It is biochemically similar to anxiety. It's caffeine.
If you have anxiety, especially panic attacks, morning anxiety, or racing thoughts, caffeine consumption is often the forgotten variable. People come off caffeine and are shocked at how much their anxiety improves within 3-7 days.
What to do: Try eliminating caffeine completely for 2 weeks. All of it: coffee, tea, chocolate, energy drinks, green tea. See if your anxiety changes. If it improves, you're a caffeine responder and need to either eliminate it or use it very minimally and only in the morning. This isn't about willpower or anxiety "spirals," it's just your neurobiology.
The blood tests you need to request
Most people with anxiety have never had comprehensive blood work looking for physical causes. They've maybe had a basic metabolic panel or a thyroid TSH. That's insufficient. Here's what you should ask for:
Essential tests: Full thyroid panel (TSH, free T4, free T3, TPO antibodies, thyroglobulin antibodies). Fasting glucose and fasting insulin. Complete iron panel (serum iron, ferritin, transferrin saturation, TIBC). Vitamin B12 and folate. RBC magnesium. Vitamin D (25-hydroxyvitamin D). High-sensitivity CRP (inflammation marker).
Additional if relevant: Comprehensive stool analysis if you have any digestive symptoms. Histamine or DAO enzyme testing if you suspect histamine intolerance. Cortisol levels if you suspect adrenal fatigue or chronic stress response issues.
If your GP won't run these tests, private companies in the UK can do them for reasonable cost. You own your body. You have the right to understand what's happening inside it. These aren't experimental. They're standard functional medicine assessment.
Get tested before accepting it's just anxiety
The mental health system has a blind spot the size of a continent. It assumes anxiety is psychological first, and only occasionally investigates whether there's something physical underneath. But anxiety symptoms can come from thyroid dysfunction, blood sugar crashes, nutritional deficiencies, gut inflammation, elevated inflammatory markers, histamine intolerance, and caffeine sensitivity.
Addressing the physical cause doesn't require you to invalidate your experience or deny that psychological factors exist. It just means getting complete information before choosing your treatment path. Someone with thyroid-induced anxiety doesn't need more cognitive behavioural therapy, they need thyroid support. Someone with reactive hypoglycemia doesn't need anxiety medication, they need dietary stabilisation. Someone with B12 deficiency doesn't need a therapist, they need B12.
Of course, some anxiety is purely psychological, and psychological approaches are valuable. But you can't know which you have until you've ruled out the physical causes. And that requires testing, which requires asking, which requires knowing these causes exist in the first place.
Your anxiety might be telling you something other than that your mind is broken. It might be telling you that your thyroid is overactive, your blood sugar is dysregulated, your gut is inflamed, or your body is nutritionally depleted. Listen to that signal. Get the tests. Find the actual cause. Then fix it.
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