Cortisol and Blood Sugar: What's Actually Linked, and Where the Wellness Trend Overreaches

Cortisol gets blamed for blood sugar swings almost as often as it gets blamed for weight gain and bad skin, and this is one of the few cases where the underlying physiology is genuinely settled rather than speculative. The complication is what has been built on top of that settled science: a fast-growing market of continuous glucose monitors, sold directly to healthy, non-diabetic consumers, that lean heavily on cortisol and stress language to justify the price tag.

The core physiology is well established. Cortisol is one of the body's main counter-regulatory hormones, meaning its job is to work against insulin and keep blood glucose from dropping too low. When cortisol rises, whether from a stressful event, a missed meal, or simply the body's normal morning peak, it prompts the liver to release stored glucose and produce new glucose through a process called gluconeogenesis, according to StatPearls' physiology reference on cortisol. This is not a malfunction. It is one of cortisol's basic, everyday functions, alongside glucagon, epinephrine, and growth hormone, and a brief blood sugar bump after a stressful morning is an expected, ordinary response, not evidence of a health problem on its own.

Where this connection becomes clinically significant is with sustained, excess cortisol. A large multicenter trial called CATALYST, led by endocrinologist John Buse at the University of North Carolina and published in Diabetes Care in 2025, screened over a thousand patients whose type 2 diabetes was difficult to control despite medication. Using a standardized dexamethasone suppression test, the researchers found that roughly 24 percent of these patients had undiagnosed hypercortisolism, meaning chronically elevated cortisol from a source independent of their diabetes. That is a real, diagnosable, testable condition, not a wellness buzzword, and it has directly changed how some endocrinologists think about hard-to-manage blood sugar.

That finding, though, describes a specific clinical population: people already struggling to control diagnosed type 2 diabetes. It does not establish that everyday stress meaningfully or lastingly disrupts blood sugar in an otherwise healthy adult, and it says nothing about whether tracking glucose day to day is a useful way to monitor stress.

That is exactly the claim now driving over-the-counter continuous glucose monitors marketed to non-diabetics. Since the FDA cleared the first over-the-counter CGM, companies have marketed the devices directly to consumers with promises of revealing how stress, not just food, moves blood sugar, positioning a glucose spike as a proxy for a cortisol spike. A 2026 review from Johns Hopkins' Bloomberg School of Public Health is more skeptical, noting that the evidence for what this data actually means for a healthy person's long-term health is scant, and that it is not established that reacting to everyday glucose fluctuations produces any measurable health benefit.

The practical distinction is straightforward even if the marketing blurs it. Proven: cortisol raises blood glucose as part of normal physiology, and chronically excess cortisol is a real, testable contributor to difficult-to-control diabetes. Unproven: that strapping on a glucose sensor to watch for stress-related spikes tells a healthy, non-diabetic person anything actionable about their cortisol or their long-term health. For most people, the better-supported response to stress-related blood sugar concerns is still the unglamorous one: consistent sleep, regular activity, and a conversation with a doctor if blood sugar control is already a diagnosed problem, not a new wearable.