Depression in executives: the biological drivers standard care misses

By Rohan Smith · Functional & Nutritional Medicine, Adelaide · Published April 29, 2026

What standard care addresses — and what it leaves out

Standard management of depression involves antidepressant medication, psychotherapy (usually CBT or ACT), and lifestyle recommendations around sleep, exercise, and stress reduction. Each of these has genuine evidence behind it. The problem is not that they don’t work — it’s that they operate at the level of symptoms and neurotransmitter availability without asking what produced the deficit in the first place.

SSRIs and SNRIs increase the availability of serotonin and noradrenaline in the synaptic cleft. That addresses part of the neurochemical picture. It does not address why serotonin production is insufficient, whether inflammation is blunting receptor sensitivity, whether thyroid hormone conversion is impaired, or whether chronic cortisol dysregulation has depleted the raw materials mood chemistry depends on.^[1]

For executives specifically, the clinical picture is often further complicated by a late presentation pattern. High-functioning people tend to adapt, compensate, and push through until the compensatory load becomes unsustainable. By the time someone presents, the underlying drivers have often been running for years. Treating the output without investigating the inputs makes sustained recovery harder to achieve.

Neuroinflammation: CRP and homocysteine

The inflammatory model of depression is one of the better-supported frameworks in contemporary mood disorder research. Meta-analyses consistently find elevated CRP and pro-inflammatory cytokines in people with major depressive disorder compared to controls, and the association holds across diverse populations and clinical settings.^[2][3]

CRP is a downstream marker of systemic inflammatory activity. Its elevation reflects upstream drivers that can include gut dysbiosis, metabolic syndrome, sleep disruption, and chronic psychological stress — all of which are common in executive presentations. When CRP is elevated alongside depressive symptoms, treating the mood alone while leaving the inflammatory source unaddressed is working against the biology.

Homocysteine is less commonly checked but arguably as informative. Elevated homocysteine — driven by suboptimal B12, folate, or B6 status, or by methylation pathway variants such as MTHFR — is associated with depressive symptom severity and late-life depression in multiple longitudinal studies.^[4][5] It also carries independent cardiovascular risk, which means it warrants assessment in the executive population for multiple reasons.

Homocysteine levels are modifiable through targeted nutritional support — which makes this a clinically useful finding rather than merely a diagnostic curiosity. See also the broader MTHFR and methylation discussion for how these pathways interact.

Thyroid function beyond TSH

TSH (thyroid-stimulating hormone) is the standard first-line thyroid test. It is a pituitary signal — it reflects how hard the pituitary is working to drive thyroid hormone production. What it does not directly measure is whether that hormone is being converted into active form at the tissue level.^[6]

T4 is the primary thyroid hormone produced by the thyroid gland. It requires conversion to T3 — the metabolically active form — in peripheral tissues, primarily the liver, kidneys, and gut. Under conditions of chronic physiological stress, caloric restriction, inflammatory load, or elevated cortisol, this conversion can shift toward producing reverse T3 (rT3) instead of free T3. Reverse T3 is metabolically inactive and can competitively block T3 receptors.^[7]

The clinical result: a patient with normal TSH and normal total T4, but with elevated rT3 and low free T3, may experience fatigue, cognitive slowing, low mood, weight gain, and poor recovery from exercise — a picture that overlaps substantially with depression. This will be missed entirely if only TSH is measured.

This pattern is particularly common in executives with years of sustained high output. The same physiological conditions that keep a high performer running — elevated cortisol, sleep compression, high demand — are the conditions that impair T3 conversion. The thyroid and metabolism page covers this mechanism in more detail.

The HPA axis: cortisol rhythm in high performers

The hypothalamic–pituitary–adrenal (HPA) axis governs the body’s cortisol response. Under normal conditions, cortisol follows a predictable diurnal rhythm: peaks in the first 30–45 minutes after waking (the cortisol awakening response), then declines steadily across the day, reaching its lowest point in the evening.

This rhythm is essential for mood regulation. Cortisol interacts directly with glucocorticoid receptors in the hippocampus — a brain region critical for emotional processing, memory consolidation, and regulation of the HPA axis itself. Sustained HPA activation, blunted morning cortisol, or a flat diurnal pattern are each associated with depressive symptoms and impaired stress recovery.^[8][9]

In the executive population, the typical pattern is not the elevated cortisol of acute stress — it is often a flattened or disrupted curve that reflects years of HPA overactivation followed by partial exhaustion. The waking cortisol response may be blunted; evening cortisol may remain elevated when it should be at its lowest. Either pattern disrupts sleep quality, impairs emotional regulation, and erodes the cognitive edge that high performers depend on.

A single morning cortisol reading provides almost no useful clinical information about this. The full diurnal curve — typically collected as four to five saliva samples across the day — tells a completely different story. For a more detailed discussion of how adrenal and stress hormone patterns present clinically, see the hormones and stress section.

The gut–brain axis: dysbiosis as an upstream driver

Approximately 90% of the body’s serotonin is produced in the enteric nervous system of the gut. The gut microbiome plays a direct role in serotonin synthesis, GABA production, and the regulation of the vagus nerve — the primary communication pathway between the gut and the brain.^[10]

When the gut microbiome is dysbiotic — characterised by reduced diversity, loss of beneficial bacterial species, and overgrowth of pathogenic or opportunistic organisms — this neurotransmitter production is compromised. Simultaneously, a dysbiotic microbiome often accompanies increased intestinal permeability: the translocation of bacterial lipopolysaccharides (LPS) across the gut wall into systemic circulation triggers a sustained low-grade inflammatory response.^[11] This systemic inflammation can cross the blood–brain barrier and directly dysregulate mood chemistry.

The connection between gut health and mood is not metaphorical. Multiple studies have now demonstrated that transferring gut microbiota from depressed individuals to germ-free animals induces depression-like behaviour in the recipients.^[12] The gut is upstream of the brain in ways that standard mood disorder treatment does not address.

For executives, the drivers of gut dysbiosis are often straightforward: years of high stress (which directly alters microbiome composition via cortisol), disrupted eating patterns, significant travel, alcohol, and antibiotic history. The gut health and IBS section covers how dysbiosis is assessed and what intervention looks like in clinical practice.

Nutritional drivers of neurotransmitter production

Serotonin synthesis requires tryptophan as a precursor, but the conversion pathway depends on co-factors including B6, zinc, and magnesium at multiple enzymatic steps. Dopamine and noradrenaline synthesis follows a separate pathway that requires tyrosine, B6, folate, and B12. Suboptimal status in any of these co-factors — which may not register as frank deficiency on a standard blood panel — can meaningfully impair neurotransmitter production.^[13]

B12 and folate are the most commonly depleted nutrients in mood disorders. Both feed the methylation cycle, which is upstream of neurotransmitter synthesis and myelin maintenance. Folate deficiency has been associated with both depressive symptom severity and poor antidepressant response; B12 insufficiency is particularly common in people over 40 and in those following plant-dominant diets.^[14][5] Because MTHFR variants affect how efficiently folate is converted to its active form, standard serum folate may appear normal while active methylfolate is functionally insufficient.

Zinc is required for BDNF (brain-derived neurotrophic factor) signalling, glutamate receptor regulation, and hippocampal neurogenesis — all of which are implicated in depression pathophysiology. Lower serum zinc is consistently found in people with major depressive disorder across meta-analyses.^[15]

Magnesium is required for over 300 enzymatic reactions, including those involved in serotonin and melatonin synthesis. It also modulates NMDA receptor activity, which is increasingly relevant given the rapid antidepressant effects seen with ketamine (an NMDA antagonist). Magnesium depletion under chronic stress is well-documented; the biochemical demand increases precisely when high-functioning people are most likely to be running low.^[16]

These nutrients are testable. The clinically useful question is not just whether levels fall within reference ranges, but whether they are optimal for the demands the individual’s system is placing on these pathways. This is the kind of granular assessment that shapes a genuinely personalised treatment approach — see the broader discussion of brain fog and mood for how these factors interact with cognitive performance.

What a functional workup actually changes

The goal of this assessment is not to replace standard depression treatment. It is to find the biological leverage points that make standard treatment more effective — or that explain why it has not worked.

Treatment-resistant depression — defined as failure to respond to two or more adequate trials of antidepressants — affects roughly 30% of patients with major depressive disorder.^[17] Clinical experience suggests that in a substantial proportion of these cases, an unaddressed biological driver is running underneath. Finding it changes the treatment strategy. It does not make the mood work or the psychological layer irrelevant. It means the person is no longer working against their own biology while trying to recover.

For executives in Adelaide seeking this level of assessment, the workup is typically completed across one to two pathology draws. Results are reviewed in context, not in isolation. The aim is to identify what is modifiable and prioritise intervention accordingly — not to hand over a supplement list, but to build a targeted clinical response based on what is actually dysregulated.

For those who are functioning but noticing the gap between how they used to feel and how they feel now, the chronic fatigue and burnout section covers how overlapping patterns are assessed in clinical practice. The assessment link below is a useful starting point.

Frequently Asked Questions

Can depression really have a physical cause?

Yes — consistently. Meta-analyses across thousands of patients show elevated inflammatory markers, thyroid conversion problems, HPA axis dysregulation, and nutrient depletions are all associated with depressive symptoms. These are not alternative explanations competing with psychological models. They are biological substrates that run underneath mood chemistry and affect how well any treatment works.

What tests should someone with treatment-resistant depression consider?

A functional medicine workup typically includes: full thyroid panel (TSH, free T3, free T4, reverse T3, TPO antibodies), high-sensitivity CRP, homocysteine, full diurnal salivary cortisol, active B12, red cell folate, serum zinc, red cell magnesium, vitamin D, and gut permeability markers if indicated. Most are accessible via standard pathology. The clinical value is in interpreting them together, not in isolation.

Does stress management help if there are biological drivers?

Yes, and the two are not separate. Chronic psychological stress is itself one of the upstream drivers of HPA dysregulation, thyroid conversion impairment, and gut microbiome disruption. Stress management reduces the physiological load. What changes with a functional workup is the ability to quantify what’s actually dysregulated and address it directly — rather than relying on lifestyle measures alone to correct a nutrient deficiency or an inflammatory process.

Is this different from seeing a psychiatrist?

A psychiatrist specialises in medication management and psychological assessment. A functional medicine workup is complementary — it looks at the biological substrate underneath the mood picture. The two approaches work together. If you’re already under psychiatric care, a functional assessment adds layers of information that psychiatric assessment typically doesn’t cover. It doesn’t replace it.

How is burnout different from depression?

Clinically, burnout and depression overlap substantially but are not identical. Burnout is characterised by emotional exhaustion, depersonalisation, and reduced efficacy — typically in relation to work context. Depression is more pervasive and persists across contexts. Recent meta-analyses suggest the two constructs share significant common variance, and in clinical practice the distinction matters less than identifying what is biologically driving the presentation.^[18] Both respond to the same kind of root-cause investigation.

Ready to find answers?

If something feels different from just being tired — and you’d like to know what’s actually driving it — a functional medicine assessment is a useful starting point. The free health assessment takes about five minutes and gives you a clear picture of where to begin.

Book a Consultation Take the Assessment

References

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