A member of my group asked whether melatonin can attenuate diabetes. This is a fascinating question because you will get opposite results with different amounts and duration.
For example, in 2022 there were two peer-reviewed studies showing opposite results when melatonin is used in the context of diabetes. One study administered 10 mg of MEL to human subjects with type 2 diabetes over the course of 12 weeks in a double ‐blinded, randomized, placebo‐controlled, crossover study. Compared to controls who received placebos, patients receiving melatonin exhibited a REDUCTION in insulin sensitivity by 12%.
However, another peer-reviewed study on diabetic rats conducted last year showed opposite results when melatonin was administered orally at 10 mg/kg body weight to rats at 6 weeks of age (emerging adulthood). The rats injected with streptozotocin to induce diabetes all exhibited a significant reduction in fasting blood glucose (FBG) and increased insulin secretion indicating β cells regeneration in the pancreas. Why would melatonin reduce hyperglycemia, hyperlipidemia and oxidative stress in diabetic rats but not humans?
The key to the controversial puzzle is in dosage and duration.
The rats were given 10 mg/kg whereas humans were given 10 mg regardless of weight
Melatonin was administered to rats for 8 weeks; whereas melatonin was given to humans for 12 weeks.
Is there a difference with these study parameters? You bet, and these differences may contribute to the opposite results obtained.
At emerging adulthood (days 70-150), one human year = 13.3 rat days [2]. That means, the rats were treated with melatonin for a duration (56 days/8 weeks) that is equivalent to ~4.2 human years. The human study gave melatonin to diabetic patients for only 3 months.
Rats were given 10 mg/kg melatonin. At an average weight of 195 grams, a rat would have
received 1.95 mg melatonin. The human equivalent dose (HED) for a 70 kg person after adjusting for interspecies differences in metabolic rate would be 160.8 mg. However, this does not account for the difference between rat and human oral bioavailability of 53.5% and 15%. [3]
The final adjusted dosage for the HED used in the successful rat experiment is actually 573.52 mg, or 57.35-fold higher than what was used in the human RCT. Furthermore, this amount was administered at 16.8 times the duration (4.2 human-year equivalent versus 3 months).
Yes, dosage and frequency matters a lot when you are supplementing with melatonin for targeted results. If you want to learn more about dosages, read my peer-reviewed paper on how to calculate HEDs from animal doses used in successful melatonin studies.
https://www.mdpi.com/1422-0067/24/6/5835
References:
[1] Lauritzen, E. S.; Kampmann, U.; Pedersen, M. G. B.; Christensen, L.-L.; Jessen, N.; Møller, N.;
Støy, J. Three Months of Melatonin Treatment Reduces Insulin Sensitivity in Patients with Type 2
Diabetes-A Randomized Placebo-Controlled Crossover Trial. J. Pineal Res. 2022, 73, e12809.
[2] Ghasemi, A.; Jeddi, S.; Kashfi, K. The Laboratory Rat: Age and Body Weight Matter. EXCLI J.
2021, 20, 1431–1445.
[3] Loh, D.; Reiter, R.J. Light, Water, and Melatonin: The Synergistic Regulation of Phase
Separation in Dementia. Int. J. Mol. Sci. 2023, 24, 5835. https://doi.org/10.3390/ijms24065835