Our Allostatic Overload piece already named HbA1c as one of the five markers in a major attempt to standardise allostatic load. It's worth its own closer look, because the mechanism behind it is a useful window into how stress stops being a feeling and starts being biology, in a way that wearables and vagal tone only partly capture.
What HbA1c measures
HbA1c reflects your average blood glucose over roughly the previous two to three months. Unlike a single finger-prick reading, it can't be skewed by what you ate this morning. That slowness is exactly what makes it useful for this conversation: it's a marker built for tracking sustained patterns, not single bad days.
The mechanism connecting stress to this number
The pathway is well established in the broader chronic stress literature. Prolonged activation of the hypothalamic-pituitary-adrenal axis and sympathetic nervous system increases cortisol and catecholamine release, which in turn promotes glucose production by the liver and reduces how effectively your cells respond to insulin. Reviews on the topic also point to a second route: chronic stress raises inflammatory signalling, including IL-6, which independently interferes with insulin signalling.
Some studies comparing physicians with and without burnout have reported higher fasting glucose and HbA1c in the burnout group, alongside higher cortisol and ACTH, though results across the wider research are mixed, as the next section explains.
Want the full evidence review?
Six biomarker systems, a reflective self-check, and what the research does and doesn't show about each.
What this is useful for
Not diagnosis. Trajectory. HbA1c sitting in the standard range (roughly 4.0 to 5.6 percent) doesn't rule out that you're running on empty, and a rise doesn't automatically mean burnout rather than diet, sleep, or another medical cause entirely. What it can do is act as one more data point, alongside how you're sleeping, your HRV trend and how you feel, that your doctor can track over time rather than interpret in isolation.
If you already get routine bloodwork, it's worth simply asking to see this number and tracking it across visits, the same way we'd suggest watching HRV as a multi-week trend rather than a single reading. One number, taken alone, tells you very little. The same number, watched over a year during a demanding period, tells you something worth paying attention to.
When a stress spike isn't diabetes
A single high reading after a brutal week at work, a bad night's sleep, or a health scare can feel like the start of a diagnosis, and it usually isn't. A 2026 review in the journal Diabetes, drawing on research funded by the American Diabetes Association's Pathway to Stop Diabetes programme, lays out the separate, faster mechanism behind this: acute stress activates neural circuits running through the brain stem, hypothalamus and amygdala that push the liver to release glucose within minutes, not months. This is a different process from the slow HbA1c drift described above, and it happens to people with and without diabetes alike.
Hospitals already use a version of this distinction. Clinicians calculate what's called the stress hyperglycaemia ratio, a patient's glucose on admission measured against their own baseline HbA1c, because a raw glucose number on its own can't tell a stress response apart from underlying dysglycaemia. A 2025 systematic review in Cardiovascular Diabetology, covering critically ill patients across conditions including heart attack, stroke and sepsis, found this ratio predicted outcomes more reliably than glucose readings alone, with both unusually low and unusually high ratios linked to worse results.
There is some evidence pointing the other way too. A Duke University trial, published in Diabetes Care, randomly assigned 108 people with type 2 diabetes to a five-session group diabetes education programme, with or without stress management training, and followed them for a year. Stress management training was linked to a small but statistically significant drop in HbA1c, about 0.5 percentage points. It was a study of people who already had diabetes, so it cannot tell us what would happen in people who do not.
So if a reading under stress looks high, the useful question isn't whether you're diabetic now. It's the same one this piece already points to: what does your HbA1c show when you're not mid-crisis, and is it worth asking your GP to check it rather than reading the meaning off one number taken on a bad day?
Sources
Findings referenced above draw on Balia et al. (Stress and Health, 2026;42(4):e70205), a systematic review of 111 studies on burnout biomarkers, which lists Deneva et al. (Medicina, 2019;55(5):209) among its studies of physicians with burnout, a 2025/2026 literature review on chronic stress, insulin resistance, and HbA1c mechanisms, Stanley (Diabetes, 2026;75(1):5–16) on the neural circuits behind acute stress hyperglycaemia, Ma et al. (Cardiovascular Diabetology, 2025;24:188) on the stress hyperglycaemia ratio in critical illness, and Surwit et al. (Diabetes Care, 2002;25(1):30–34) on stress management and long-term glycaemic control.
Start with a baseline
The Stress Biomarker Checklist
A 13-page evidence review covering six biomarker systems, a reflective self-check, and what the research does and doesn’t show about each. Free.
Start with the Self-Check on page 11. It takes about four minutes.
The Capio Initiative is an educational platform, not a medical practice. The biomarkers discussed here help explain stress physiology. None of them can diagnose burnout, and we never use them to diagnose anything. Speak with a qualified healthcare professional before changing anything about your recovery or your use of tracking devices.
