A rare case report suggests that melatonin supplementation could potentially modulate blood sugar levels in insulinoma patients, offering a new perspective amid ongoing debates about its metabolic effects.
A case report published in JCEM Case Reports has raised the possibility that melatonin may have eased dangerous low blood sugar episodes in a woman with a rare insulin-producing pancreatic tumour, offering an unusual counterpoint to long-standing concerns that the supplement can interfere with glucose control. The report, written by Thanh Nguyen and Aleksey Matveyenko of the Mayo Clinic and Galina Smushkin of the University of British Columbia, describes a 64-year-old patient whose hypoglycaemia became markedly less frequent after she began taking over-the-counter melatonin for sleep, before surgery later confirmed that her tumour carried melatonin receptors.
The woman had spent about five years experiencing episodes of blurred vision and profound fatigue, usually in the afternoon, roughly two to three hours after lunch, and improving when she ate. On two occasions, she was taken to emergency care after becoming confused and developing slurred speech, and doctors initially considered atypical migraine as a possible explanation. That pattern was unusual for insulinoma, a rare pancreatic tumour that secretes insulin even when blood sugar is already low. A 2024 review in The Journal of Clinical Endocrinology & Metabolism said symptoms most often appear during fasting, although a minority of patients notice problems after meals.
A 14-day continuous glucose monitor showed that her blood sugar was below 70 mg/dL for 40% of the time and below 54 mg/dL for 19% of the time, with the lowest readings clustering later in the day. Doctors then documented a spontaneous episode during an afternoon blood draw: her glucose had fallen to 22 mg/dL, while insulin and C-peptide levels remained inappropriately high. Imaging revealed an 11-millimetre mass in the tail of the pancreas, allowing clinicians to avoid the prolonged fast often used when low blood sugar cannot be caught in real time.
While she was waiting for surgery, the patient began taking 10 mg of melatonin at bedtime for insomnia. She later reported that her lows seemed less severe, and her glucose monitor broadly supported that account. In the two weeks before she started the supplement, she spent 31% of the time between 54 and 69 mg/dL and 19% below 54 mg/dL. In the first two weeks after starting melatonin, those figures dropped to 19% and 1%. Over the 30 days before her operation, time spent between 54 and 69 mg/dL fell to 7%, with only 1% below 54 mg/dL.
Surgeons removed a 1-centimetre, well-differentiated neuroendocrine tumour with clear margins. Tissue testing then found a strong, though uneven, pattern of melatonin receptor expression, which the authors say could help explain why the supplement appeared to blunt insulin release. They wrote that further studies are needed to determine whether activating melatonin receptor signalling might have a protective role in insulinoma. After surgery, the patient’s blood sugar briefly climbed to 270 mg/dL and she needed short-term intravenous insulin, but she was discharged without medication and had no symptoms at six weeks.
The report comes at a time when melatonin’s effect on metabolism is drawing more scrutiny. A June 2026 trial from Mass General Brigham and the Broad Institute, published in Diabetes Care, found that a single 5 mg dose worsened glucose tolerance in healthy adults carrying a common diabetes-risk variant in the melatonin receptor gene MTNR1B, while a recent systematic review and meta-analysis of 30 randomised trials found that melatonin supplementation significantly reduced fasting glucose, insulin levels and insulin resistance measures, although the findings were highly variable. A separate meta-analysis of eight trials also reported lower insulin and improved insulin sensitivity, while another review found little change in fasting glucose but a modest fall in fasting insulin. Together, those studies suggest melatonin can affect glucose regulation, but in ways that may differ according to genetics, dose and the underlying condition being studied.
For this patient, however, the key point is that the evidence remains limited to one case. The timing of her improvement could reflect other changes, including the natural course of the disease, and the authors do not claim melatonin as a treatment for insulinoma. Surgery remains the standard approach, with removal of the tumour considered the treatment of choice in the 2024 review. Even so, the case offers a striking reminder that a supplement often discussed for its potential risks may, in a very specific setting, have seemed to work in the opposite direction.
Disclaimer: This content is for informational purposes only and is not intended to be a substitute for professional medical judgment, advice, diagnosis, or treatment.
