Two patients share a birthday. Both turn 58 this year. One has the vascular tone, immune reserve, and stamina of a man ten years younger. The other already carries the lab profile of someone approaching 70. Their charts agree on age. Their bodies do not.
Chronic stress has long been a suspect in explaining that gap, and cortisol has long been the hormone used to measure it. A 2025 study in Biogerontology, drawing on 969 American adults, tested how well cortisol actually performs in that role. The answer was that cortisol alone performs poorly, and that reading it against a second adrenal hormone performs considerably better.
Why a Single Cortisol Level Misleads
Cortisol moves constantly. It surges in the early morning, tapers through the day, and reacts to whatever is happening the moment blood is drawn. A tense phone call, a short night, or the needle itself will register. One reading captures a moment rather than a pattern, which makes it a weak instrument for separating a bad Tuesday from ten hard years.
A second problem runs deeper. Sustained stress does not simply park cortisol at a high level. It wears down the hypothalamic-pituitary-adrenal axis, the signaling loop between brain and adrenal gland, and one hallmark of that wear is a flattened cortisol response. Someone years into caregiving or financial pressure may show a low morning cortisol. On paper, the value looks fine. Physiologically, it is anything but.
The Counterweight
Dehydroepiandrosterone-sulfate, or DHEA-S, is the most abundant steroid circulating in the human body. It clears slowly and lacks the pronounced daily rhythm of cortisol, making it a more stable measure.
Functionally, it opposes cortisol. As a glucocorticoid antagonist, DHEA-S softens cortisol’s effects on immunity, the brain, and metabolism. Sustained cortisol suppresses immune function and, at high enough levels for long enough, damages neurons in the hippocampus and cortex. DHEA-S supports immune activity, offers neuroprotection, and improves mood. Laboratory work has shown that DHEA blocks cortisol-driven lymphocyte death and lowers susceptibility to viral infection, while cortisol pushes the other way.
Two trajectories then converge with age. Adrenal DHEA-S output falls steadily as the adrenal cortex thins, and it falls further under sustained stress. Studies of family caregivers and of workers reporting heavy occupational strain have documented lower DHEA-S than in matched comparison groups. Deep into chronic stress, in what researchers call the exhaustion phase, both hormones lose responsiveness as the axis dysregulates.
The same holds for the ratio. Cortisol wanders. DHEA-S declines. What connects them answers a question neither one answers alone: whether the brake still matches the accelerator.
Reading Age in the DNA
Your genetic sequence does not change with the years. The chemical tags sitting on it do. Methyl groups attach to and release from specific positions along the genome in patterns that shift on a fairly predictable schedule. Reading methylation across a defined set of those positions yields an estimate of biological age. Subtract the birthday on the chart, and the remainder is called epigenetic age acceleration, abbreviated EAA. A positive value means the body is running ahead of the calendar.
These estimates earn attention because they predict things that matter, including illness, cognitive decline, and death from any cause. They also connect to stress in a mechanistically sensible way. Many of the methylation sites built into these clocks sit within or beside glucocorticoid response elements, the DNA sequences that respond to cortisol signaling. Stress physiology and the aging clock share the same genomic real estate.
Six clocks were tested, and they are not equivalent tools. Hannum reads 71 sites and tracks shifts in neutrophils, lymphocytes, monocytes, and the CD4/CD8 ratio, tying it tightly to immune aging. PhenoAge draws on 513 sites linked to inflammation and DNA damage. The skin and blood clock, often called Horvath2, refines the original Horvath method by incorporating blood markers. GrimAge folds in plasma proteins and smoking history. DunedinPACE, built from two decades of longitudinal tracking, reports a rate of aging rather than an age.
What the Researchers Measured
Data came from the Midlife in the United States study, a long-running national research project. DHEA-S was drawn from fasting blood collected before 7 a.m. Cortisol came from 12-hour overnight urine collections, which average out momentary spikes that distort single blood draws. Whole blood supplied the methylation profiles.
Three questions followed. Do age, sex, and demographic background shape these hormones? Once we account for chronological age, do the hormones predict epigenetic age? And which measure performs best, cortisol, DHEA-S, or the ratio between them?
The Findings
Demographic results tracked decades of prior work. DHEA-S fell with age, and age alone accounted for roughly 24% of the variation in DHEA-S levels, making it by far the dominant influence. Men ran higher than women, consistent with testosterone stimulating adrenal DHEA-S production. Cortisol came in lower in women and declined with age, with a steeper slope among African American participants that matches earlier reports of a blunted cortisol awakening response in the same Milwaukee population. The ratio climbed with age and was higher in women, with the age-related increase clear in Caucasian participants and not statistically significant among African American participants.
Then the central comparison. After adjusting for chronological age, sex, and demographic group, the ratio outperformed either hormone measured alone. It correlated with epigenetic age on three of the six clocks: Horvath2, Hannum, and PhenoAge. Cortisol alone was significant on one clock, Hannum. DHEA-S alone reached significance on none.
Epigenetic age acceleration told a sharper story. Looking specifically at the gap between biological and chronological age, only the ratio showed a significant association, and only with the Hannum clock. A higher cortisol/DHEA-S ratio corresponded to a faster rate of aging regardless of how many birthdays a person had accumulated.
Which clocks responded is itself informative. Hannum and PhenoAge are the two most closely tied to immune function and inflammation, exactly where cortisol and DHEA-S pull against each other. Patients with chronic inflammatory bowel disease who show high cortisol alongside low DHEA-S have been found to carry greater inflammatory activity. The signal appeared where the underlying biology predicted it would.
Where the Findings Stop
Effect sizes were modest. Cortisol and the ratio accounted for something between 0.5% and 1.1% of the variance in epigenetic data beyond chronological age, and the ratio’s contribution to Hannum acceleration was roughly 0.8%. Real, but small.
Other constraints deserve naming. Cortisol came from urine while DHEA-S came from blood. The investigators deliberately left out body measurements, health questionnaires, lifestyle, and socioeconomic data, wanting to see what these hormones could do on their own. That decision almost certainly cost them explanatory power and may explain why GrimAge and DunedinPACE, both of which incorporate smoking history, showed nothing. Most African American participants came from one Milwaukee neighborhood, which limits how far the demographic findings travel. And because this is a snapshot rather than a follow-up study, it establishes association without proving cause.
None of that erases the practical lesson. Cortisol by itself would have turned up almost nothing here. DHEA-S by itself would have turned up nothing at all. Together they turned up something.
Running the Calculation
The math takes one step. Divide cortisol by DHEA-S, keeping both in the same units.
In practice, that means a fasting morning blood draw, ideally between 7 and 9 a.m., with serum cortisol and serum DHEA-S both reported in mcg/dL. Dividing cancels the units, leaving a bare number. A 45-year-old man with a cortisol of 12 mcg/dL and a DHEA-S of 240 mcg/dL lands at 0.05. A 68-year-old woman with a cortisol of 14 mcg/dL and a DHEA-S of 45 mcg/dL lands at 0.31.
Several habits keep that number honest. Match the units on both sides, since cortisol is often reported in mcg/dL or nmol/L while DHEA-S may appear in mcg/dL or mcmol/L, and a mismatched ratio compares to nothing. Avoid mixing sample types, because salivary cortisol measures the free hormone while serum measures total hormone bound to carrier proteins. Account for oral estrogen, whether prescribed as hormone therapy or contraception, which raises cortisol-binding globulin and inflates total serum cortisol without altering the free fraction. Finally, repeat the test the same way each time, same hour, fasting, same laboratory.
The research team took a different route, pairing overnight urinary cortisol with fasting morning serum DHEA-S and then taking the natural logarithm of the result, since raw hormone ratios prove unstable and unusually sensitive to measurement error. Their participants averaged about 113 mcg/dL for DHEA-S and about 1.61 mcg/dL for overnight urinary cortisol, yielding a raw ratio near 0.04. Those figures describe a urine-based measurement and will not line up with a serum ratio from your own report.
Interpreting the Number
Begin with what nobody can give you. No professional society publishes a validated target for the cortisol/DHEA-S ratio, and the neat optimal-range tables posted on wellness sites rest on no outcome data whatsoever. Treat any precise ideal figure with skepticism.
Age- and sex-specific reference intervals for DHEA-S, by contrast, are well established. Mayo Clinic Laboratories reports men at 105-728 mcg/dL for ages 18-30, 57-522 at 31-40, 34-395 at 41-50, 20-299 at 51-60, 12-227 at 61-70, and 6.6-162 from 71 onward. Women run 83-377 mcg/dL at 18-30, 45-295 at 31-40, 27-240 at 41-50, 16-195 at 51-60, 9.7-159 at 61-70, and 5.3-124 from 71 onward.
Notice how wide those windows are. Falling inside one says very little. Notice too how steeply they drop by decade, which sets the trap built into age-adjusted reporting: a woman of 70 sitting squarely mid-range holds a small fraction of what she carried at 25, and nothing on the report gets flagged. Sitting in the upper half of your age band makes a more useful working goal than merely staying unflagged, with the caveat that no trial has shown a specific DHEA-S target changes outcomes.
Morning cortisol intervals differ by laboratory and assay, generally landing somewhere near 6-18 mcg/dL for a draw between 6 and 10 a.m. That variability is another reason to keep both hormones from the same laboratory.
For the ratio itself, one published threshold stands out. Among 108 adults aged 65 and older with type 2 diabetes, a morning serum cortisol/DHEA-S ratio at or above 0.2 (both values in mcg/dL) emerged as the strongest independent risk factor for sarcopenia, with odds nearly 8 times higher after adjustment. DHEA-S under 73 mcg/dL and cortisol at or above 9.3 mcg/dL also signaled risk in that group. Given the small and specific population, 0.2 works better as a flag worth investigating than as a universal cutoff. It remains the only number anyone has tied to a hard clinical outcome.
Related work points the same way. In a separate analysis, adults in the highest cortisol/DHEA-S quartile carried significantly greater odds of low natural killer cell activity, a finding that held in men, premenopausal women, and postmenopausal women, and that fits the immune-aging signal the epigenetic study picked up.
Something usable comes out of this. In midlife, a morning serum ratio well under 0.2 with DHEA-S in the upper half of your age-adjusted range describes a reassuring pattern. Women generally run higher ratios than men, and everyone drifts upward with the decades, so the comparison that teaches you the most is not against a population table. It is against your own result from a year ago, drawn the same way at the same lab. A ratio rising faster than your birthdays is the finding that deserves a response.
Putting It to Work
Chronic stress isn’t just something you feel. It leaves a chemical residue on your DNA that can be read and compared against your date of birth. That is a sobering fact and a hopeful one, because a measurable burden is a burden you can address.
If you or your physician are evaluating stress physiology, a lone cortisol value is thin evidence. Order DHEA-S alongside it and calculate the ratio yourself, since most panels report the two hormones separately and no lab will do the arithmetic for you. A falling DHEA-S paired with a steady or rising cortisol is a pattern that calls for attention rather than reassurance, particularly past midlife, given the associations between low DHEA-S and depression, chronic pain, weakened immunity, cognitive decline, and cardiovascular risk.
Recovery is built into the body’s design, and the stress axis was made to swing in both directions. Sleep, genuine rest, regular movement, real food, and durable human and spiritual connection are the inputs that let the brake work as intended. The ancient practice of setting a day aside for rest has measurable biochemistry beneath it.
Bloodwork makes all of this concrete. A cortisol and DHEA-S pair is inexpensive, widely available, and belongs beside the metabolic and inflammatory markers in any comprehensive panel. Measure it, watch the trend, and act on what the trend tells you.
Interpreting the result is where a knowledgeable healthcare partner earns their keep. A cortisol and DHEA-S pair is easy to order and easy to misread, and the ratio has to be weighed against your age, your sex, your medications, your sleep, your training load, and everything else competing for your adrenal output. A licensed physician or nurse practitioner trained in integrative or functional medicine will read those numbers as part of a whole picture rather than in isolation, distinguish a pattern that calls for intervention from one that simply reflects the decade you are in, and track the trend across repeat testing at the same laboratory. That kind of partnership also protects against the opposite error, which is chasing a hormone level with supplements or replacement therapy that carries real risks and no proven benefit for aging. Bring the numbers to someone qualified to interpret them, and let the conversation start there.
References
- Suh E, Cho A-R, Haam J-H, Gil M, Lee Y-K, Kim Y-S. Relationship between serum cortisol, dehydroepiandrosterone sulfate (DHEAS) levels, and natural killer cell activity: a cross-sectional study. J Clin Med. 2023;12(12):4027.
- Takeshita RSC, Nguyen AT, Auger AP, Chung WCJ. Cortisol, DHEAS, and the cortisol/DHEAS ratio as predictors of epigenetic age acceleration. Biogerontology. 2025;26:164.
- Yanagita I, Fujihara Y, Kitajima Y, Tajima M, Honda M, Kawajiri T, et al. A high serum cortisol/DHEA-S ratio is a risk factor for sarcopenia in elderly diabetic patients. J Endocr Soc. 2019;3(4):801-813.
