Overview.
Anxiety affects approximately 30% of adults at some point. While most anxiety is psychological, several medical conditions present primarily as anxiety — and are readily treatable once identified. Hyperthyroidism, blood sugar instability, cortisol dysregulation, and nutrient deficiencies (magnesium, vitamin D, B12) can all mimic or exacerbate anxiety. A targeted lab workup rules out medical mimics and ensures treatment targets the right cause.
Medical anxiety differs from purely psychological anxiety in that it often has sudden onset, occurs without clear triggers, is accompanied by physical symptoms disproportionate to the situation, and may not respond to typical anxiety management strategies. Medical causes should be considered especially when anxiety is new-onset, atypical, or treatment-resistant.
Prevalence: Anxiety disorders affect ~30% of adults at some point. Medical causes account for approximately 5-10% of anxiety presentations. Hyperthyroidism is the most common medical mimic. Anxiety from blood sugar instability (reactive hypoglycaemia) is increasingly recognised.
What to test.
First-line tests
- TSH — Hyperthyroidism is the most common medical mimic of anxiety — causes palpitations, tremor, weight loss, and anxiety indistinguishable from panic disorder.
- Fasting Glucose + HbA1c — Blood sugar instability (reactive hypoglycaemia, prediabetes) causes anxiety, shakiness, irritability, and rapid heartbeat that resolve with eating.
- CBC — Anaemia causes tachycardia and anxiety-like symptoms. Iron deficiency specifically affects dopamine function and may worsen anxiety.
- CMP (Metabolic Panel) — Screens for electrolyte abnormalities (calcium, sodium), liver dysfunction, and kidney function — all of which can cause neuropsychiatric symptoms.
Second-line tests
- Vitamin D — Vitamin D receptors are present in the brain. Deficiency is associated with increased anxiety and depression risk in observational studies.
- Vitamin B12 — B12 deficiency causes neuropsychiatric symptoms including anxiety, depression, and cognitive dysfunction. More common in vegetarians/vegans and older adults.
- Magnesium (RBC Magnesium preferred) — Magnesium modulates the HPA stress axis and GABA receptor function. Deficiency is associated with increased anxiety. Serum magnesium misses intracellular depletion — RBC magnesium is more accurate.
- Ferritin — Iron is a cofactor for dopamine and serotonin synthesis. Low ferritin (even without anaemia) is associated with anxiety, restless legs, and poor stress tolerance.
Specialized tests
- Morning Cortisol / Cortisol Rhythm — Cushing's syndrome (excess cortisol) causes anxiety, insomnia, weight gain, and hypertension. Consider if features suggest hypercortisolism. Adrenal insufficiency causes anxiety through different mechanisms (hypotension, hypoglycaemia).
- Testosterone (Men) — Low testosterone in men is associated with increased anxiety, irritability, and depression. Consider if anxiety coexists with low libido, fatigue, and erectile dysfunction.
- Free T3 / Full Thyroid Panel — If TSH is borderline or low-normal with persistent anxiety symptoms, T3 thyrotoxicosis may be present. Full thyroid panel reveals subclinical hyperthyroidism.
Common causes.
- Hyperthyroidism — Anxiety with palpitations, tremor, weight loss, heat intolerance, loose stools
- Blood Sugar Instability / Reactive Hypoglycaemia — Anxiety episodes 2-4 hours after meals, relieved by eating. Shakiness, rapid heartbeat, irritability, confusion.
- Iron Deficiency — Anxiety with fatigue, tachycardia, poor concentration, restless legs
Diagnostic patterns.
- Low TSH + high Free T4 + anxiety + tremor + weight loss — likely Hyperthyroidism. Next step: Endocrinology referral; thyroid antibodies and uptake scan
- Normal labs + significant life stressors + response to therapy — likely Primary anxiety disorder (GAD, panic disorder). Next step: CBT, SSRI/SNRI, lifestyle modification; medical workup provides reassurance
- Low ferritin + low B12 + anxiety + fatigue + vegetarian diet — likely Nutritional deficiency-driven anxiety. Next step: Iron and B12 supplementation; reassess anxiety in 2-3 months
- Post-meal anxiety + shakiness relieved by eating + elevated fasting insulin — likely Reactive hypoglycaemia / insulin resistance. Next step: Low-glycaemic diet, reduce refined carbohydrates, assess HOMA-IR
Lifestyle.
Non-medical causes
- Generalised anxiety disorder (GAD)
- Panic disorder
- Social anxiety disorder
- PTSD / trauma-related anxiety
- Caffeine excess (>400mg/day — common and underrecognised cause)
- Alcohol withdrawal (even from moderate regular use)
- Cannabis use (THC can worsen anxiety in some individuals)
- Sleep deprivation
- Medication side effects (corticosteroids, stimulants, thyroid hormone excess, decongestants)
Considerations
- Assess caffeine intake — reduce to <200mg/day or eliminate as a trial
- Regular aerobic exercise (30 minutes, 5x/week) — as effective as SSRIs in some studies
- Sleep hygiene — anxiety and insomnia are bidirectional
- Alcohol assessment — both use and withdrawal worsen anxiety
- Mindfulness/meditation — evidence-based for anxiety reduction
- Screen time reduction, especially before sleep
FAQs.
Should I get blood work if I've been diagnosed with anxiety?
Yes, at least once — especially if your anxiety is new-onset, treatment-resistant, or has physical features (palpitations, tremor, weight changes). Basic thyroid, metabolic, and nutritional screening takes one blood draw and can identify treatable causes. Normal results are also valuable — they confirm the anxiety is not medical and treatment can focus on psychological approaches.
Can low magnesium cause anxiety?
Yes. Magnesium modulates GABA receptors (calming neurotransmitter) and the HPA stress axis. Deficiency is common (affects ~20% of adults) and associated with increased anxiety. Serum magnesium is a poor test — it only drops when depletion is severe. RBC magnesium is more accurate. Supplementation (glycinate or threonate forms) may help even if levels are low-normal.
My anxiety gets worse after eating — what could that be?
Post-meal anxiety with shakiness and rapid heartbeat suggests reactive hypoglycaemia — a blood sugar crash 2-4 hours after eating. It's often driven by insulin resistance and a high-glycaemic diet. Check fasting insulin and HbA1c. Treatment: lower glycaemic index foods, protein with every meal, avoid refined carbohydrates.