Melatonin Supplement May Reduce Dangerous Blood Sugar Drops Prior to Insulinoma Surgery

Researchers have long warned that melatonin can dampen insulin secretion. For a 64‑year‑old woman with a rare insulin‑producing tumor, that same effect may have worked to her advantage.

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 perilous blood‑sugar crashes became far less frequent after she began taking over‑the‑counter melatonin for sleep. The tumor later excised from her pancreas was found to harbor melatonin receptors, offering a plausible explanation for the patterns recorded by her glucose monitor.

Five Years of Afternoon Crashes After Lunch

For roughly five years, the woman experienced episodes of blurred vision and fatigue that typically emerged “mostly in the afternoons 2 to 3 hours after lunch” and improved after eating. On two occasions, spaced two years apart, she suffered emergencies marked by altered consciousness and slurred speech. Neurologists initially considered atypical migraines.

That timing is atypical. Insulinomas are pancreatic neoplasms that secrete insulin even when glucose is already low. A 2024 review in The Journal of Clinical Endocrinology & Metabolism notes that symptoms “occur mainly in the fasting state,” although up to 20 % of patients also report post‑prandial episodes. These tumors are exceedingly rare, with an incidence of roughly 0.7 to 4 cases per million individuals per year.

A 14‑day continuous glucose monitor traced the pattern. Her glucose fell below 70 mg/dL 40 % of the time and dropped under 54 mg/dL 19 % of the time. The lows clustered in the afternoon and evening, while overnight and morning readings remained normal.

Physicians captured a spontaneous episode during an afternoon blood draw. Her glucose measured 22 mg/dL—far beneath normal—yet her insulin and C‑peptide concentrations did not fall as expected. Because the hypoglycemia was documented in real time, the team avoided the prolonged 72‑hour fast that the review recommends when spontaneous hypoglycemia cannot be confirmed. Imaging revealed an 11‑mm mass in the tail of her pancreas.

The Melatonin Effect Showed Up in Her Glucose Data

Awaiting surgery, the woman began self‑administering 10 mg of melatonin at bedtime to alleviate insomnia. She continued the supplement for about four months and reported to her clinicians that her low‑glucose episodes seemed less frequent and less severe.

Her glucose monitor corroborated her observation. In the two weeks before melatonin, she spent 31 % of the time between 54 and 69 mg/dL and 19 % below 54 mg/dL. During the first 14 days on melatonin, those figures decreased to 19 % and 1 %. In the 30 days preceding her operation, the proportion between 54 and 69 mg/dL fell to 7 % with only 1 % below 54 mg/dL.

Surgeons excised a 1‑cm, well‑differentiated neuroendocrine tumor with clear margins. When the tissue was stained with an antibody that detects melatonin receptors, they observed “robust, albeit heterogeneous melatonin receptor expression pattern in the tumor tissue.”

The authors hypothesize that melatonin may have acted on those receptors to restrain 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 discontinued melatonin prior to surgery. Post‑operatively, her blood glucose transiently surged to 270 mg/dL, necessitating a brief course of intravenous insulin. She was discharged without any medication. At six weeks, she remained asymptomatic, and her monitor indicated just 2 % of the time between 54 and 69 mg/dL.

The Same Hormone That Raises Diabetes Concerns

The case is notable because melatonin’s insulin‑dampening action is usually regarded as a disadvantage.

In June 2026, investigators from Mass General Brigham and the Broad Institute reported a small randomized, double‑blind crossover trial in Diabetes Care. They administered a single 5‑mg dose of melatonin to 21 healthy adults on one day and a placebo on another. According to a Mass General Research Institute summary, melatonin “significantly worsened glucose tolerance” in carriers of a common diabetes‑risk variant in the melatonin receptor gene MTNR1B, while noncarriers showed no effect. The hormone also attenuated the pancreas’s early insulin response to rising glucose.

For most individuals, a blunted insulin response is unfavorable. In a patient whose tumor overproduces insulin, however, it may prove beneficial, and the Mayo‑led report suggests the tumor itself expressed the receptors melatonin targets.

One Patient, Many Open Questions

The report details a single case and cannot establish that melatonin caused the improvement. Dietary changes or the natural history of her disease were not excluded in a controlled setting, and it remains uncertain how a bedtime dose influenced lows that predominantly occurred in the afternoon.

The receptor staining was patchy, and the antibody employed could not discriminate between melatonin receptor subtypes. It is unknown how frequently insulinomas exhibit this trait. Surgical resection remains the standard of care. The 2024 review endorses removal of a solitary tumor as the preferred treatment, with five‑year survival for slowly growing insulinomas ranging from 94 % to 100 %.

In the United States, melatonin is marketed as a dietary supplement, a category that the FDA oversees less stringently than prescription or over‑the‑counter drugs. Anyone experiencing unexplained episodes of confusion, blurred vision, or shakiness—particularly after meals—should seek clinical evaluation rather than self‑treat with supplements.

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 surgical removal of the tumor.

Why was this woman’s case unusual?

Her low blood sugar episodes arose 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 excised tumor displayed strong, though uneven, melatonin receptor expression.

Does this mean melatonin treats insulinoma?

No. This is a solitary observation, and the authors urge further investigation. 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 harboring a common diabetes‑risk gene variant. Individuals with blood‑sugar concerns should discuss supplement use with a clinician.

How did a glucose monitor help?

Two weeks of continuous monitoring revealed that her lows clustered in the afternoon and evening, which aided clinicians in pursuing the diagnosis.

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