The Relationship of Endogenous Nocturnal Melatonin Levels and Heart Rate in Healthy Young Males

Objectives: Light inhibits the secretion of melatonin produced in the pineal gland, while darkness increases its release. Melatonin may affect cardiologic functions, including heart rate and blood pressure. In this study, we evaluated the relationship between endogenous nocturnal melatonin levels and heart rate in healthy young males. Methods: Twenty-four healthy males [mean age: 22.4±2.4 (18–26) years] who did not have any disease and did not smoke, drink alcohol, or use drugs were included in the study. While the subjects were in the supine position at a time point between 02:30 and 04:30 am, plasma samples were taken to measure melatonin concentrations. After centrifugation, plasma samples were immediately frozen at -20°C until analysis. In each subject, heart rate and arterial blood pressure were measured by the same observer. Results: Although we found a significant negative correlation between nocturnal melatonin levels and age (p=0.02, r=-0.46), we did not find any correlation between melatonin and body mass index (p=0.80, r=0.05), waist circumference (p=0.12, r=-0.31), hip circumference (p=0.77, r=-0.06), systolic blood pressure (p=0.79, r=-0.05), diastolic blood pressure (p=0.71, r=-0.07), mean blood pressure (p=0.95, r=-0.01), or pulse pressure (p=0.51, r=-0.14). Additionally, we found a negative correlation between nocturnal melatonin levels and heart rate, which did not reach statistical significance (p=0.86, r=-0.038). Conclusion: The current study demonstrated a negative correlation that did not reach statistical significance between endogenous nocturnal melatonin levels and heart rate in healthy young males.