Effects of bedtime melatonin treatment on blood pressure and arterial stiffness: a three-month, randomized, placebo-controlled crossover study in individuals with type 2 diabetes mellitus.

AIM: Blood pressure is regulated in part by circadian rhythms, and melatonin has been reported to exert blood pressure-lowering effects. The underlying mechanisms, however, remain unclear. We hypothesized that melatonin would lower blood pressure in individuals with type 2 diabetes with or without hypertension, and that this effect would be mediated by a reduction in arterial stiffness. METHODS: We conducted a double-blinded, randomized, placebo-controlled crossover trial involving 17 individuals with type 2 diabetes. Participants completed two treatment phases: three months of 10 mg melatonin taken one hour before nighttime, and three months of placebo taken at the same time separated by a four-week washout period. On the last day of each period, participants underwent 24-hour ambulatory blood pressure monitoring, including measurement of arterial stiffness, using the Arteriograph 24. Fifteen participants completed the 24-hour ambulatory blood pressure monitoring (hypertension n = 6). RESULTS: Melatonin treatment was associated with numerical, non-significant reductions in mean nighttime systolic blood pressure (-6 [-13:1] mmHg, p = 0.08, ≈ 5% decrease) and diastolic blood pressure (-5 [-11:1] %, p = 0.11). The pulse wave velocity as a measure for arterial stiffness was unaffected by melatonin treatment (p = 0.83). CONCLUSION: In this randomized placebo-controlled trial of individuals with type 2 diabetes, 3 months of treatment with 10 mg melatonin administered one hour before bedtime did not significantly affect blood pressure or pulse wave velocity. Although numerical reductions in nighttime blood pressure were observed, these hypothesis-generating findings were not statistically significant and warrant confirmation in larger studies specifically powered for blood pressure outcomes.