You have been told it is stress. Or anxiety. Or that this is just how things feel in your thirties, your forties, after a difficult year. Maybe you have been prescribed something. Maybe you have tried therapy, meditation, a better sleep routine. And maybe none of it has moved the needle the way you expected. Because no one has looked at what your body is actually doing.
Here is why blood tests and mood belong in the same conversation
A prospective cohort study from the UK Biobank, following 433,890 participants over five years, found that abnormal values on standard clinical laboratory tests predicted the development of major depressive disorder, including markers of liver function, inflammation, and metabolic health that are almost never discussed in the context of mood [1]. These are not experimental biomarkers. They are the same tests sitting in your GP’s test menu, rarely ordered together, rarely interpreted through the lens of mental health.
Blood tests do not diagnose depression or anxiety. That is psychiatry’s domain, and the distinction matters. What blood tests can do is the following: reliably, with good evidence behind them, is identify biological contributors to mood instability that are correctable.
Thyroid dysfunction that looks like depression. Inflammation that mimics burnout. Hormone imbalances that have been causing mood swings for years without anyone connecting them to the blood. Testing these markers does not replace professional mental health support. It sits alongside it, and sometimes changes everything.
The brain is a metabolically voracious organ. It requires constant glucose, oxygen, and a precisely regulated hormonal environment to function as expected. Thyroid hormones govern the speed at which neurons fire. Iron is a cofactor in dopamine synthesis, when ferritin falls, dopamine production slows. Vitamin D receptors are expressed throughout the limbic system and prefrontal cortex, the brain regions most involved in mood regulation and executive function. Oestradiol and progesterone modulate serotonin and GABA signalling: which is why perimenopause, with its fluctuating hormones, can feel biochemically like mood whiplash. Cortisol at chronically elevated levels reorganises the brain’s threat-detection circuitry, making anxiety a near-permanent state rather than an appropriate response to actual threats.
None of this is controversial in neuroscience. Much of it is invisible in general practice, where a 10-minute consultation focused on the presenting symptom leaves no room for the biological audit that a mood problem sometimes genuinely requires.
The blunt truth: no blood test diagnoses depression, anxiety, bipolar disorder, or any other mood condition. Psychiatric diagnosis requires clinical assessment: symptom history, functional impact, differential diagnosis, and professional judgement. What blood tests reveal is whether there are additional biological drivers making those symptoms worse, more resistant to treatment, or potentially responsible for them in the first place. The distinction matters because treating a thyroid condition can resolve symptoms that would otherwise have been managed as primary depression for years.
If you have been experiencing persistent low mood, mood swings, irritability, or anxiety and have never had a comprehensive blood panel, that gap is worth closing. Aniva’s panel includes the full set of markers most relevant to mood biology: thyroid, inflammation, hormones, vitamin D, B12, iron, and metabolic markers. All in a single annual test. Join the free waitlist →
The thyroid connection to mood is among the best-established in all of medicine and simultaneously among the most consistently missed in practice. The mechanism is direct: thyroid hormones regulate almost every metabolic process in the brain, including the production and sensitivity of serotonin, dopamine, and noradrenaline.
The neurotransmitters most associated with mood disorders. Patients with hypothyroidism can present with a clinical picture nearly indistinguishable from major depression: low mood, reduced motivation, cognitive slowing, fatigue, and social withdrawal. Patients with hyperthyroidism can present with a picture nearly indistinguishable from anxiety disorder: racing thoughts, irritability, palpitations, difficulty sleeping, and panic-like episodes.
The overlap is not metaphorical. A 2009 review in the European Thyroid Journal documented that thyroid responses frequently normalise alongside successful treatment of depression, and that depression should be considered in all patients with thyroid dysfunction [2]. The HPT axis, hypothalamic-pituitary-thyroid, is functionally interconnected with the HPA axis (the stress response), meaning thyroid dysfunction and mood disorders share overlapping biological circuitry.
The classic picture of hypothyroidism, lower activity of your thyroid gland than normal, includes cold intolerance, weight gain, constipation, and dry skin. But the psychiatric presentation, the one that ends up in front of a GP as “depression”, often comes first. Slowed thinking. Flattened affect. Inability to feel pleasure. Pronounced fatigue that worsens over months. These symptoms can develop gradually enough that the patient adapts to them, attributing them to stress or age rather than recognising them as the signs of a thyroid that has gradually stopped working at full capacity.
Subclinical hypothyroidism, where TSH is elevated but still within the laboratory’s “normal” range, typically defined as 0.4–4.0 mIU/L, is particularly problematic. Many patients with TSH between 2.5–4.0 mIU/L, combined with positive thyroid antibodies indicating Hashimoto’s disease, experience mood and cognitive symptoms even though their TSH falls within the technical normal range. Treating based on the TSH number alone, without context from free T3, free T4, and antibody status, misses this group entirely.
TSH measures what the pituitary is signalling: not what the thyroid is producing, nor what the peripheral tissues are receiving. Free T4 measures actual thyroid output. Free T3 measures the active hormone that enters cells and drives cellular metabolism. The conversion from T4 to T3 can be impaired by chronic stress, nutrient deficiencies (selenium, zinc), and inflammation: meaning a patient can have a normal TSH and normal T4 while cellular hypothyroidism is developing at the tissue level. The großes Blutbild tests none of this. The standard GP thyroid screen tests TSH alone.
Thyroid peroxidase antibodies (TPO-Ab) identify Hashimoto’s autoimmune thyroiditis, which can cause mood and cognitive symptoms through episodic thyroid inflammation years before TSH moves outside the reference range. Testing for it early is how you catch the problem before it becomes a decade-long psychiatric misdiagnosis.
One of the most significant developments in psychiatry over the past twenty years has been the recognition that depression is, in a meaningful proportion of cases, an inflammatory phenomenon. This is not a fringe hypothesis. It is supported by meta-analyses of tens of thousands of patients and is actively shaping how treatment-resistant depression is being investigated and managed.
A 2019 systematic review and meta-analysis published in Psychological Medicine, pooling 37 studies covering 13,541 depressed patients and 155,728 controls, found that approximately 27% of patients with depression showed low-grade inflammation (CRP >3 mg/L), and that over half (58%) showed mildly elevated CRP (>1 mg/L) [3]. The meta-analytic odds ratio for elevated CRP in depression was 1.47 (95% CI 1.18–1.82). This means depressed individuals were nearly 50% more likely than matched healthy controls to have elevated CRP: even after adjusting for confounders including BMI and antidepressant treatment.
A separate meta-analysis of 107 studies covering over 10,000 patients confirmed CRP as significantly elevated in depression, with an effect size of g=0.71 (95% CI 0.50–0.92) [4]. The finding is robust. The question it raises for any individual is whether they are in the inflammatory subgroup, and that question has a straightforward answer: measure their hs-CRP.
The biological mechanism explains the connection elegantly. When the immune system activates: during infection; chronic stress; or ongoing inflammatory conditions, it releases pro-inflammatory cytokines including IL-6 and IL-1β. These cytokines cross the blood-brain barrier and induce what researchers call sickness behaviour: fatigue, social withdrawal, reduced motivation, loss of pleasure, disrupted sleep, and cognitive slowing. Anyone who has had influenza recognises this as a complete description of a depressive episode. The difference between infection-induced and chronic-inflammation-induced sickness behaviour is primarily duration — the flu resolves, but chronic low-grade inflammation from metabolic dysfunction, gut permeability, or autoimmune activity does not.
Cortisol dysregulation also drives this pathway. Chronic cortisol elevation promotes inflammatory signalling, which then feeds back to worsen cortisol rhythm, creating a self-reinforcing loop that makes both stress management and mood regulation progressively harder.
The inflammation finding is not merely academic. Elevated CRP at baseline predicts poorer response to antidepressants in randomised controlled trials. Suggesting that for the inflammatory subgroup, standard first-line pharmacotherapy is working against a biological headwind that the medication does not address. Anti-inflammatory interventions (exercise, dietary change, omega-3 supplementation, treatment of underlying inflammatory conditions) in patients with elevated CRP have shown antidepressant effects in RCTs. Knowing your hs-CRP before embarking on a treatment pathway is clinically relevant information. Not simply a curiosity.
hs-CRP below 1.0 mg/L = low inflammatory load. Above 3.0 mg/L = elevated, worth investigating regardless of mood symptoms. If you have been struggling with mood and have never measured your inflammatory baseline, this is one of the most informative single tests available. See the full Aniva biomarker list →
Vitamin D is more helpful to think of as an hormone than as a vitamin. In that light, it's impact on mood becomes clearer than often realised. The association between vitamin D and mood is one of the most studied, and most debated, relationships in nutritional psychiatry.
The big picture: the observational evidence is strong and consistent; the intervention trials show more mixed results. But the mechanistic case is compelling enough, and the population-level deficiency in Northern Europe significant enough, that testing vitamin D status is a clinical priority for anyone experiencing mood problems in Germany or Finland.
Here is how it works. Vitamin D receptors are expressed in the hippocampus, prefrontal cortex, cingulate gyrus, and hypothalamus, regions central to mood regulation, stress response, and emotional processing. Vitamin D regulates the gene transcription of tryptophan hydroxylase 2, the enzyme responsible for serotonin synthesis in the brain. It also modulates the activity of monoamine oxidase (MAO), which breaks down serotonin, dopamine, and noradrenaline.
In other words, vitamin D does not just passively sit in brain tissue. It participates in the biochemistry that determines whether the brain produces and maintains adequate neurotransmitter levels.
Several large epidemiological studies have found inverse associations between vitamin D levels and depression risk. The seasonal pattern of affective disorders, worse in autumn and winter in northern latitudes, better in summer, mirrors the seasonal variation in vitamin D levels with considerable precision, though light-mediated serotonin pathways and circadian disruption also contribute.
The northern European vitamin D data is particularly relevant: the Robert Koch Institut found that roughly 56% of German adults fall below 50 nmol/L, the threshold most researchers associate with inadequate tissue function [5].
Standard vitamin D supplementation recommendations of 400–1,000 IU daily are calibrated for population-level bone health, not for raising a severely depleted individual from 25 nmol/L to 75 nmol/L. Pharmacokinetically, someone starting at 25 nmol/L typically needs 3,000–5,000 IU daily to reach optimal range within three to four months. Someone already at 60 nmol/L supplementing at 5,000 IU could reach toxicity-adjacent levels within the same period.
The mood benefit of vitamin D supplementation, where it exists, appears dose- and duration-dependent, as well as dependent on the starting level. Supplementing “standard” doses at “normal” baseline levels produces little effect. Aggressively correcting genuine deficiency in depleted individuals is a different intervention. The only way to know which situation applies to you is to test first, supplement to a target, and retest to confirm you have reached it.
The biological connection between sex hormones and mood is one of the most clinically underappreciated in general practice. Oestradiol and progesterone modulate serotonin receptor sensitivity, GABA receptor activity, and the production of allopregnanolone, a neurosteroid with intrinsic anxiolytic properties. When these hormones fluctuate or decline. At perimenopause, postpartum, or during phases of high physiological stress, the neurochemical environment they have been maintaining can destabilise rapidly.
Perimenopause is not a single event. It is a transition of typically 4–10 years during which oestradiol levels fluctuate dramatically before eventually declining. This fluctuation , rather than the final low-oestrogen state, is what drives mood instability in many women: erratic serotonin signalling, disrupted sleep architecture, increased cortisol sensitivity, and reduced GABA tone. Women who have never experienced notable mood problems can develop anxiety, irritability, emotional volatility, and low mood in their early to mid-forties that is genuinely perplexing to them and frequently misdiagnosed as anxiety disorder or depression.
Testing oestradiol, progesterone, and FSH together provides the hormonal context. A rising FSH indicates the pituitary is working harder to stimulate increasingly unresponsive ovaries, the biochemical signature of perimenopause. Combined with erratic oestradiol (high on some days, low on others), it explains the clinical picture in a way that “stress” or “anxiety” does not.
Low testosterone in women is associated with reduced motivation, flattened affect, fatigue, and diminished sense of wellbeing, a picture often described as “depression” or “burnout.” A global consensus position statement published in Climacteric in 2019 recognised testosterone therapy for appropriately selected women with hypoactive sexual desire disorder, acknowledging the broader evidence for testosterone’s role in female wellbeing [6]. Despite this, testosterone is rarely measured in women presenting with mood symptoms in standard practice.
Critically, total testosterone without SHBG gives misleading information. SHBG binds testosterone and renders it biologically inactive. A woman with normal total testosterone and high SHBG may have chronically low free testosterone, the fraction that actually enters cells and drives effect. Caloric restriction, oral contraceptives, liver stress, and hyperthyroidism all raise SHBG. For a woman on the pill experiencing persistent low mood, measuring SHBG alongside testosterone is clinically essential.
Testing oestradiol, progesterone, testosterone, SHBG, FSH, and LH together provides a complete hormonal picture that a partial panel cannot. Aniva’s panel includes the full sex hormone panel alongside thyroid, inflammation, and metabolic markers. All in a single blood draw. Join the waitlist →
The hypothalamic-pituitary-adrenal (HPA) axis is the body’s central stress-response system. Chronic activation, whether from work pressure; relationship stress; financial anxiety; or any sustained perceived threat; drives cortisol to remain elevated above its normal diurnal pattern. As we have written in detail about cortisol, a flattened cortisol awakening response (CAR), where morning cortisol fails to spike appropriately, is associated with burnout, low motivation, and anhedonia. Chronically elevated evening cortisol disrupts sleep architecture, reduces slow-wave sleep, and impairs the overnight restoration processes the brain relies on.
The UK Biobank study referenced above identified hypercortisolism among the strongest biomarker predictors of subsequent major depression: consistent with decades of prior research linking HPA axis hyperactivation to depression onset [1].
DHEA-S (dehydroepiandrosterone sulphate) is the most abundant steroid hormone in the human body, produced by the adrenal glands as a precursor to sex hormones. It counterbalances cortisol: where cortisol is catabolic and immunosuppressive at high levels, DHEA-S is generally anabolic, neuroprotective, and supports resilience to stress. The ratio between cortisol and DHEA-S has been proposed as a more informative marker of adrenal stress state than either in isolation. A high ratio: elevated cortisol or depressed DHEA-S, characterises the exhausted, depleted presentation that many people recognise as burnout. DHEA-S declines naturally with age (by roughly 80% from peak to old age), but premature DHEA-S depletion relative to cortisol in younger adults reflects sustained adrenal strain.
Neurotransmitters are not conjured from nothing. Their synthesis requires raw materials. Serotonin requires tryptophan as a precursor, and the conversion depends on several cofactors including iron (for tryptophan hydroxylase) and B vitamins. Dopamine requires tyrosine, iron, copper, and B6. The methylation cycle: which regulates gene expression, neurotransmitter metabolism, and numerous neurological processes, depends critically on B12 and folate. When any of these raw materials are deficient, neurotransmitter synthesis is compromised at the biochemical level.
Vitamin B12 deficiency produces a neurological and psychiatric syndrome that includes cognitive slowing, depression, irritability, memory impairment, and fatigue — virtually indistinguishable from primary mood disorders in many cases. Proton pump inhibitors (widely prescribed in Germany for acid reflux), metformin, advancing age, and restrictive diets all impair B12 absorption. Standard blood panels do not include B12. The großes Blutbild’s MCV elevation — large red blood cells — can suggest B12 deficiency as a secondary sign, but by the time MCV shifts, B12 has typically been depleted for some time. Direct measurement catches it earlier.
Methylmalonic acid (MMA) is a more sensitive marker of functional B12 deficiency than serum B12 alone — serum B12 can appear normal while functional deficiency exists. For patients with neurological or mood symptoms and borderline B12, adding MMA testing significantly improves diagnostic sensitivity.
Iron is a cofactor in tyrosine hydroxylase, the rate-limiting enzyme in dopamine synthesis. Low ferritin, even in the absence of clinical anaemia, reduces the enzymatic capacity for dopamine production. The clinical picture of dopamine insufficiency overlaps substantially with depression: anhedonia (inability to experience pleasure), low motivation, difficulty concentrating, and a flattened reward response. This is one reason why iron deficiency frequently presents with mood and cognitive symptoms that resolve with iron repletion, independent of haemoglobin. The full iron-ferritin picture matters here: serum iron, ferritin, and transferrin saturation together reveal the functional iron status that haemoglobin alone cannot.
The connection between insulin resistance and mood is increasingly recognised but rarely tested in the context of mental health. Insulin resistance impairs glucose transport into brain cells, particularly neurons in the prefrontal cortex, reducing the brain’s energy supply in a regionally specific way that affects executive function, mood regulation, and impulse control. The UK Biobank study found that metabolic markers, including indicators of glucose dysregulation, predicted 5-year depression incidence independently of other variables [1].
The classic pattern: afternoon energy crashes, difficulty concentrating after carbohydrate-rich meals, carbohydrate cravings as a coping mechanism for low energy, and persistent mood instability that worsens when meals are delayed. These are not personality traits. They are the physiological consequences of impaired glucose regulation — and they are identifiable with fasting insulin, HbA1c, and fasting glucose. As our article on blood sugar and metabolism covers in depth, fasting insulin is the earliest marker of this dysfunction. The one that moves before glucose, before HbA1c, and well before any clinical diagnosis.
If you have been experiencing persistent mood instability, unexplained anxiety, low mood, or emotional volatility and want to understand whether there are measurable biological contributors, this is what a rational comprehensive panel looks like:
Thyroid: TSH, free T4, free T3, TPO antibodies, Tg antibodies. Not TSH alone.
Inflammation: hs-CRP. The single most informative marker for identifying whether an inflammatory subtype of mood disorder is likely.
Vitamin D: 25-hydroxyvitamin D. Particularly important if you live above 50°N latitude and test in winter.
Sex hormones: Oestradiol, progesterone, testosterone, SHBG, FSH, LH. Essential if mood symptoms are cyclical, perimenopausal, or associated with hormonal contraception.
Adrenal: Cortisol (morning serum), DHEA-S. Context for the HPA axis state and stress adaptation.
Nutritional: Vitamin B12, folate, ferritin (with serum iron and transferrin saturation).
Metabolic: Fasting insulin, HbA1c, fasting glucose. Especially relevant if mood symptoms correlate with energy crashes or carbohydrate intake.
None of these are exotic. All are available as standard blood tests. The challenge, as with hair loss and with chronic fatigue and with a dozen other symptom clusters that sit at the intersection of conventional medicine and preventive health, is that they are rarely ordered together, rarely interpreted in context, and rarely presented back to a patient as a coherent biological story. That gap is exactly what comprehensive preventive testing is designed to close.
Aniva’s annual membership at €199 covers all of the above in a single blood draw at an ISO 15189-certified German laboratory, with a personalised results report that interprets your findings in the context of your symptoms and goals — not just against a reference range. Join the free waitlist →
Persistent mood instability, anxiety, and low mood are not always primary psychological conditions. In a meaningful proportion of cases, they reflect measurable biological dysfunction that remains undetected because the right markers are never tested.
Thyroid dysfunction, including subclinical hypothyroidism and early Hashimoto’s, produces a clinical picture nearly identical to depression or anxiety and requires TSH, free T3, free T4, and antibodies to identify reliably.
Chronic inflammation is present in approximately 27% of depressed patients at CRP >3 mg/L, predicts worse treatment response to antidepressants, and responds to targeted intervention. Vitamin D deficiency is endemic in Northern Europe and affects neurotransmitter synthesis pathways directly. Sex hormone imbalances, particularly in perimenopause, post-contraception, or high-stress periods, destabilise serotonin and GABA signalling in ways that feel indistinguishable from primary anxiety or depression.
Ferritin below optimal range impairs dopamine synthesis. Insulin resistance reduces prefrontal cortical energy supply in ways that manifest as mood and cognitive symptoms before any clinical diagnosis is reached.
Treating the biology alongside the psychology is not a compromise. For a significant proportion of people, it is the missing half of the picture.
→ Explore the Aniva biomarker panel | Join the free waitlist
1. Wium-Andersen MK et al. “Clinical laboratory tests and five-year incidence of major depressive disorder: a prospective cohort study of 433,890 participants from the UK Biobank.” Translational Psychiatry. 2021;11:370. Nature
2. Dayan CM, Panicker V. “Hypothyroidism and depression.” European Thyroid Journal. 2009;4(Suppl 2):3–9. PubMed
3. Osimo EF et al. “Prevalence of low-grade inflammation in depression: a systematic review and meta-analysis of CRP levels.” Psychological Medicine. 2019. 37 studies; 13,541 depressed patients; 155,728 controls. PMC6712955
4. Köhler-Forsberg O et al. “Inflammatory markers in depression: A meta-analysis of mean differences and variability in 5,166 patients and 5,083 controls.” Brain, Behavior, and Immunity. 2020;88:901–911. PubMed
5. Rabenberg M et al. “Vitamin D status among adults in Germany — DEGS1.” BMC Public Health. 2015;15:641. PMC4530987
6. Davis SR et al. “Global consensus position statement on the use of testosterone therapy for women.” Climacteric. 2019;22(5):429–434. PubMed
7. Orsolini L et al. “C-Reactive Protein as a Biomarker for Major Depressive Disorder.” International Journal of Molecular Sciences. 2022;23(3):1616. 56 studies reviewed. PMC8836046
8. Sullivan PF et al. “The hypothalamic-pituitary-thyroid axis in major depression.” Acta Psychiatrica Scandinavica. 1997;95:370–378.
9. Howren MB, Lamkin DM, Suls J. “Associations of depression with C-reactive protein, IL-1, and IL-6: a meta-analysis.” Psychosomatic Medicine. 2009;71(2):171–186. PubMed
10. Vaucher P et al. “Effect of iron supplementation on fatigue in nonanemic menstruating women with low ferritin.” CMAJ. 2012;184(11):1247–1254. PubMed
This content is for informational purposes only and is not medical advice. It does not constitute a diagnosis of any mental health condition, and blood test results should never replace assessment by a qualified mental health professional or physician. Mood disorders have multiple causes and require comprehensive evaluation. If you are experiencing significant or persistent mental health symptoms, please consult a qualified healthcare professional. If you are in crisis, contact a crisis helpline or emergency services immediately.
