Measuring Stress Biomarkers: Cortisol, HRV & IL-6 | YEARS

Stress Biomarkers: How Stress Can Be Measured in the Body

You feel stressed. This is not purely a psychological experience, but a biological reality that can leave measurable traces in your body. The subjective feeling of stress can be deceptive: you may get used to constant strain and eventually perceive a chronically elevated level of stress as normal. Biological measurements can provide additional information about physiological systems that may be affected by prolonged stress. Determining which methods are scientifically sound is more complex than looking at a single blood value.

This article explains which stress biomarkers are meaningful in a clinical context, how they interact, and where their limitations lie.

Why Stress is Biologically Measurable

Stress is your body's reaction to a challenge. Acute stress, like right before an important presentation, is adaptive. It sharpens your senses and mobilizes energy. The body releases catecholamines (adrenaline, noradrenaline) and cortisol, your heart rate accelerates, and your blood pressure rises. After the challenge, the system normalizes again.

Chronic stress arises when the strain persists and recovery phases are absent. Prolonged stress can dysregulate three central biological systems:

1. The neuroendocrine system: The hypothalamic-pituitary-adrenal axis (HPA axis), which is controlled via cortisol.
2. The autonomic nervous system (ANS): The balance between the activating sympathetic nervous system and the regenerating parasympathetic nervous system.
3. The immune system: Chronic stress can promote low-grade, systemic inflammation.

Self-perception is often a poor guide here. Through habituation, we eventually perceive a constantly high load as normal. Other people have difficulty identifying and describing their own feelings (alexithymia). Still others cognitively downplay their own strain. Nevertheless, physiological changes associated with prolonged stress may still be measurable.

Modern preventive medicine can therefore use different biomarkers to characterize physiological systems that may be affected by chronic stress.

Measuring Cortisol: The Most Famous Stress Biomarker and Its Limits

Cortisol is arguably the most well-known stress hormone. It is produced in the adrenal cortex and is the central effector hormone of the HPA axis. Its main task: to provide the body with energy in the form of glucose to deal with a stressful situation.

The crucial characteristic of cortisol is its pronounced diurnal rhythm. The concentration rises sharply around waking to prepare us for the day. A distinct increase during the first 30–45 minutes after awakening is known as the Cortisol Awakening Response (CAR). Over the course of the day, cortisol levels generally decline, reaching their lowest point around midnight.

A single cortisol value in the blood is hardly usable for assessing chronic stress. A morning blood draw only shows one point in time and cannot distinguish between normal circadian variation and a stress-related change.

For meaningful assessment of HPA-axis activity, there are better methods:

• Salivary cortisol daily profile: Repeated saliva samples distributed over the day can characterize the diurnal cortisol curve. If the Cortisol Awakening Response is specifically assessed, several tightly timed samples during approximately the first 30–60 minutes after awakening are required.
• 24-hour urine collection: Measures the total amount of free cortisol excreted over 24 hours. This method provides information about overall cortisol production but does not capture the diurnal rhythm and is primarily used in endocrinological diagnostics.
• Serum cortisol (fasting in the morning): Less suitable for assessing chronic psychological stress. This measurement is primarily useful in the evaluation of endocrine disorders such as Cushing's syndrome or adrenal insufficiency.

Chronic stress and exhaustion have been associated in some studies with altered diurnal cortisol patterns, including flatter slopes, changes in the Cortisol Awakening Response, or altered HPA-axis responsiveness. Findings are heterogeneous, however, and no single cortisol pattern is sufficiently specific to diagnose chronic stress or burnout.

The measurement is also disrupted by numerous factors: caffeine, intense exercise, sleep deprivation, acute psychological stress, nicotine and medications such as oral contraceptives can influence the values. A careful medical history and standardized measurement conditions are therefore essential. The methodology for valid cortisol measurement in saliva is scientifically well-investigated (Hellhammer et al., Psychoneuroendocrinology, 2009).

DHEA-S and the Cortisol/DHEA-S Ratio

Cortisol is accompanied by other adrenal hormones, including DHEA (dehydroepiandrosterone) and its storage form DHEA-sulfate (DHEA-S).

DHEA-S is an androgen that has been investigated for neuroprotective, immunomodulatory, and other biological effects. Unlike cortisol, DHEA-S does not have such a pronounced diurnal rhythm. Its concentration in the blood is relatively stable, making it a suitable candidate for a single blood measurement.

In stress research, researchers have therefore investigated not just absolute cortisol and DHEA-S concentrations, but also the ratio between the two hormones. The cortisol/DHEA-S ratio has been studied as a potential marker of HPA-axis regulation, chronic stress, and exhaustion.

An elevated cortisol/DHEA-S ratio may indicate an imbalance between glucocorticoid and adrenal androgen activity. Studies have associated changes in this ratio with chronic exhaustion and burnout (Theorell et al., PLoS One, 2013). However, the ratio is not an established standalone clinical measure of allostatic load, and its diagnostic and prognostic value remains insufficiently validated for routine clinical use.

When interpreting this, age must be taken into account. DHEA-S production peaks in early adulthood and declines continuously thereafter (adrenopause). A 50-year-old naturally has lower DHEA-S values than a 30-year-old, which influences the quotient. An abnormal value is not independent proof of a disease, but rather one piece of information within the overall picture of physiological stress regulation.

Due to its relevance for a broader picture of the HPA axis, the measurement of cortisol and DHEA-S is part of the YEARS Evolve® Program. This extended hormone status is not included in the baseline YEARS Core® Program.

Heart Rate Variability (HRV): The Functional Stress Indicator

Heart rate variability does not measure the heart rate itself, but the temporal variability of the intervals between individual heartbeats. A healthy heart does not beat like a metronome. The small irregularities are a sign of adaptability and a well-functioning autonomic nervous system.

HRV reflects autonomic regulation and is particularly influenced by the parasympathetic nervous system, whose main nerve is the vagus nerve.

• Higher HRV is generally associated with greater parasympathetic modulation and greater autonomic adaptability.
• Lower HRV can reflect reduced parasympathetic modulation and lower autonomic flexibility. Psychological stress is one of many factors that can reduce HRV. Chronically low HRV has also been associated with increased cardiovascular risk and higher all-cause mortality.

HRV can be measured in several ways:

• Short-term measurement (5 minutes): An ECG is recorded and analyzed under standardized resting conditions. This is a well-established method for standardized short-term HRV assessment.
• Long-term measurement (24 hours): A Holter monitor captures HRV over an entire day and night, providing insights into autonomic regulation across everyday activities and sleep.
• Wearable-based measurement: Smartwatches and rings usually measure HRV at night and provide average values. They are well-suited for trend monitoring in everyday life but are less standardized than clinical ECG measurements.

The strength of HRV is simultaneously its weakness: it is an extremely dynamic marker. Acute stress, sleep quality, intense training, illness, or alcohol consumption the night before can immediately and significantly influence HRV. A single measurement thus remains a snapshot. HRV becomes especially meaningful over time, when trends become visible over weeks and months.

At YEARS, we conduct a standardized, clinical HRV test as part of the Core® Program to establish a baseline of autonomic function.

Inflammation Markers: How Chronic Stress Can Affect IL-6 and CRP

An often-overlooked consequence of chronic stress is its potential effect on the immune system. Persistent psychological stress can influence inflammatory signaling through complex biological pathways, including activation of NF-κB and increased production of pro-inflammatory cytokines.

Two central markers in this context:

1. Interleukin-6 (IL-6): A cytokine that can respond to acute psychosocial stress. IL-6 has therefore been studied as a marker of stress-associated inflammatory responses, although its interpretation depends heavily on context.
2. High-sensitivity C-reactive protein (hs-CRP): IL-6 stimulates the production of CRP in the liver. hs-CRP is more stable and very well validated as a marker for low-grade, systemic inflammation. Chronically elevated hs-CRP values are considered an established cardiovascular risk marker.

Numerous studies demonstrate associations between chronic psychosocial stress, poor sleep, and elevated inflammation markers.

However, inflammation markers are not stress-specific. An acute infection, obesity, autoimmune diseases, metabolic disease, smoking, or intense exercise can also increase hs-CRP and IL-6. Psychosocial stress can contribute to inflammatory signaling, but elevated IL-6 or hs-CRP cannot establish stress as the cause of inflammation. Their diagnostic value therefore depends strongly on the broader clinical context.

Due to its stability and clinical significance, hs-CRP is part of the 87-biomarker panel in the YEARS Core® Program. The more sensitive IL-6 is measured in the extended panel of the Evolve® Program.

Salivary Alpha-Amylase: A Sensitive Marker for Acute Stress

In addition to the HPA axis, there is a second, faster stress system: the sympatho-adrenomedullary (SAM) system. It is responsible for the rapid release of adrenaline and noradrenaline. A biomarker closely linked to sympathetic activation is salivary alpha-amylase (sAA).

This digestive enzyme is produced primarily by the salivary glands, whose function is strongly influenced by the autonomic nervous system. During acute stress, sAA activity can rise within minutes, often faster than cortisol. However, sAA also shows substantial diurnal variation, which must be taken into account when sampling.

In stress research, sAA is a promising marker. However, it has not yet established itself in routine clinical diagnostics for several reasons:

• High variability: Values fluctuate strongly between individuals and within a single day.
• Confounding factors: Food intake, chewing gum, oral health, dry mouth, and certain medications can significantly influence the measurement. Pre-analytical standardization is demanding.

Salivary alpha-amylase therefore remains more of a tool for research than for broad clinical application. For this reason, sAA measurement is not part of the YEARS programs. We focus on measurements that currently provide clearer clinical information for a prevention strategy.

Which Combination of Stress Biomarkers Makes Sense for Chronic Stress

No single biomarker can reliably measure or diagnose chronic psychological stress. There is also currently no validated biomarker panel that can determine an individual's overall chronic stress burden with a single score.

Several carefully selected measurements can, however, provide complementary information about biological systems that may be affected by prolonged stress:

1. Daily cortisol profile (saliva): To assess HPA-axis dynamics and circadian cortisol regulation. A dedicated multi-sample protocol is required if the Cortisol Awakening Response is assessed.
2. DHEA-S (serum): To provide additional information about adrenal androgen activity and its relationship with HPA-axis regulation.
3. Heart rate variability (clinical short-term measurement): To assess autonomic regulation and parasympathetic modulation.
4. hs-CRP (serum): As a stable, validated marker of low-grade systemic inflammation.
5. IL-6 (serum): As a more dynamic marker of inflammatory signaling.

Every single value must always be interpreted by a doctor in the context of the other findings as well as your individual life situation, medical history, and symptoms. What these diagnostics can achieve is a more detailed characterization of physiological systems that may be affected by chronic stress.

A standalone diagnosis of burnout or chronic psychological stress cannot be derived from these biomarkers, nor can the psychosocial causes be identified through laboratory testing alone. The diagnostics create a data-based starting point for targeted interventions, whether in the areas of sleep, nutrition, exercise, or specific stress management techniques.

How YEARS Implements Stress Diagnostics in Practice

At YEARS, comprehensive stress diagnostics are not an isolated test, but part of our holistic prevention programs. Biomarkers and functional diagnostics are combined to create a broader picture of your health.

The YEARS Core® Program lays the foundation here. It contains stress-relevant measurements such as the clinical HRV test to capture autonomic regulation, as well as the measurement of hs-CRP as part of the 87-biomarker panel.

For more comprehensive stress-related diagnostics, the YEARS Evolve® Program is designed. In addition to all the services from Core®, it includes:

• An extended hormone panel with cortisol and DHEA-S
• The measurement of Interleukin-6 (IL-6) in the extended inflammation panel
• The analysis of biological clocks, which can provide additional information about broader biological aging processes. These measures cannot, however, determine how much of an individual's biological aging is attributable specifically to psychological stress.

This data foundation forms the basis for the YEARS Strategy Session. You discuss all results with one of our doctors and receive not raw lab values, but an integrated analysis with concrete, prioritized recommendations for action. For executives under particular strain, this is a central component of the Manager Check-up at YEARS.

The subsequent coaching sessions in the YEARS Evolve® Program help you translate these recommendations into everyday life and develop effective strategies for stress reduction.

If you want to better understand physiological systems that may be affected by chronic stress and develop a data-based strategy for greater resilience, reach out to us.

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Disclaimer

Stress diagnostics at YEARS serve the purpose of prevention and the assessment of physiological parameters that may be influenced by chronic stress. They do not diagnose psychological stress or burnout and do not replace psychotherapeutic or psychiatric diagnostics and treatment for manifest psychological disorders.

Sources

1. Hellhammer, D. H., Wüst, S., & Kudielka, B. M. (2009). Salivary cortisol as a biomarker in stress research. Psychoneuroendocrinology, 34(2), 163–171. DOI: 10.1016/j.psyneuen.2008.10.026
2. Slavich, G. M. (2019). The new field of human social genomics: Developing a scientifically based, clinically useful, and transdiagnostic model of stress-related physical and psychological disease. Psychosomatic Medicine, 81(2), 122–127.
3. Thayer, J. F., Åhs, F., Fredrikson, M., Sollers, J. J., & Wager, T. D. (2012). A meta-analysis of heart rate variability and neuroimaging studies: Implications for heart rate variability as a marker of stress and health. Neuroscience & Biobehavioral Reviews, 36(2), 747–756.
4. Theorell, T., Osika, W., Leineweber, C., Magnusson Hanson, L. L., Hultcrantz, M., & Westerlund, H. (2013). Is the cortisol/DHEA-S ratio a marker of exhaustion? A longitudinal study. PLoS One, 8(10), e78373. DOI: 10.1371/journal.pone.0078373