Researchers have warned for years that melatonin can weaken the body's insulin response. For a 64-year-old woman with a rare insulin-producing tumor, that same effect may have worked in her favor.
In a case report published in JCEM Case Reports in April 2026, Thanh Nguyen and Aleksey Matveyenko of Mayo Clinic and Galina Smushkin of the University of British Columbia describe a patient whose dangerous blood sugar crashes became far less frequent after she began taking over-the-counter melatonin for sleep. The tumor later removed from her pancreas contained melatonin receptors, offering a possible explanation for what her glucose monitor recorded.
Five Years of Afternoon Crashes After Lunch
For about five years, the woman had episodes of blurry vision and exhaustion that came "mostly in the afternoons 2 to 3 hours after lunch" and improved when she ate. Twice, two years apart, she had emergencies involving altered consciousness and slurred speech. Neurologists first suspected unusual migraines.
That timing was unusual. Insulinomas are pancreatic tumors that release insulin even when blood sugar is already low. A 2024 review in The Journal of Clinical Endocrinology & Metabolism notes that symptoms "occur mainly in the fasting state," though up to 20% of patients also report symptoms after meals. The tumors are rare, with an estimated 0.7 to 4 cases per million people each year.
A 14-day continuous glucose monitor revealed the pattern. Her glucose was below 70 mg/dL 40% of the time and below 54 mg/dL 19% of the time. The lows clustered in the afternoon and evening, while her overnight and morning readings were normal.
Doctors then caught a spontaneous episode during an afternoon blood draw. Her blood sugar was 22 mg/dL, far below normal, yet her insulin and C-peptide levels had not dropped as they should. Because the low was captured in real time, the team did not need the prolonged 72-hour fast that the review recommends when hypoglycemia cannot be documented spontaneously. Scans found an 11-millimeter mass in the tail of her pancreas.
The Melatonin Effect Showed Up in Her Glucose Data
While she waited for surgery, the woman started taking 10 mg of melatonin at bedtime on her own to help with insomnia. She took it for about four months and told her doctors her low blood sugar episodes seemed less frequent and less severe.
Her glucose monitor supported her account. In the 14 days before melatonin, she spent 31% of the time between 54 and 69 mg/dL and 19% below 54 mg/dL. In her first 14 days on melatonin, those figures fell to 19% and 1%. In the 30 days before her operation, time between 54 and 69 mg/dL dropped to 7%, with 1% below 54 mg/dL.
Surgeons removed a 1-centimeter, well-differentiated neuroendocrine tumor with clean margins. When the team stained the tissue with an antibody that detects melatonin receptors, they found "robust, albeit heterogeneous melatonin receptor expression pattern in the tumor tissue."
The authors propose that melatonin may have acted on those receptors to hold back insulin release. They wrote that "future studies are warranted to explore whether pharmacological and/or genetic activation of the melatonin receptor signaling plays a protective role" in insulinoma.
She stopped melatonin before surgery. Afterward, her blood sugar briefly swung high, reaching 270 mg/dL and requiring intravenous insulin for a short time. She went home on no medications. At six weeks, she had no symptoms, and her monitor showed just 2% of the time between 54 and 69 mg/dL.
The Same Hormone That Raises Diabetes Concerns
The case is striking because melatonin's insulin-dampening effect is usually seen as a drawback.
In June 2026, researchers from Mass General Brigham and the Broad Institute published a small randomized, double-blind crossover trial in Diabetes Care. They gave 21 healthy adults a single 5 mg dose of melatonin on one day and a placebo on another. According to a Mass General Research Institute summary, melatonin "significantly worsened glucose tolerance" in people carrying a common diabetes-risk variant in the melatonin receptor gene MTNR1B, but not in noncarriers. It also reduced the pancreas' early insulin response to rising blood sugar.
For most people, a weaker insulin response is not good news. For a patient whose tumor pumps out too much insulin, it may be a different story, and the Mayo-led report suggests the tumor itself carried the receptors melatonin acts on.
One Patient, Many Open Questions
The report describes a single patient and cannot prove that melatonin caused her improvement. Changes in diet or the natural course of her disease were not ruled out in a controlled way, and it is not clear how a bedtime dose affected lows that came mostly in the afternoon.
The receptor staining was uneven, and the antibody used could not tell which melatonin receptor type was involved. It is unknown how many insulinomas share this feature. Surgery remains the standard treatment. The 2024 review calls removal of a single tumor the treatment of choice, and five-year survival for slow-growing insulinomas reaches 94% to 100%.
In the United States, melatonin is sold as a dietary supplement, which the FDA regulates less strictly than prescription or over-the-counter drugs. Anyone with unexplained episodes of confusion, blurred vision, or shakiness, especially after meals, should see a clinician rather than try to treat it on their own.
Key Questions Answered
What is an insulinoma?
It is a rare pancreatic tumor that releases insulin even when blood sugar is already low. Most are slow-growing and can be cured by surgically removing the tumor.
Why was this woman's case unusual?
Her low blood sugar episodes came mainly two to three hours after lunch rather than during fasting, which is the more typical pattern for insulinoma.
What did melatonin appear to do?
After she began taking 10 mg at bedtime, her monitor showed time below 54 mg/dL falling from 19% to 1%. Her removed tumor showed strong, though uneven, melatonin receptor expression.
Does this mean melatonin treats insulinoma?
No. This is one case, and the authors call only for further study. Surgery remains the standard treatment.
Can melatonin affect blood sugar in other people?
A 2026 Diabetes Care trial found that a single 5 mg dose worsened glucose tolerance in healthy adults carrying a common diabetes-risk gene variant. People with blood sugar concerns should discuss supplements with a clinician.
How did a glucose monitor help?
Two weeks of continuous monitoring showed that her lows clustered in the afternoon and evening, which helped doctors pursue the diagnosis.
Published by Medicaldaily.com
