The Impact of Alcohol on Sleep Physiology: A Prospective Observational Study on Nocturnal Resting Heart Rate Using Smartwatch Technology

<b>Background/Objectives:</b> Alcohol consumption is known to influence cardiovascular regulation and sleep quality; however, real-world data on its acute effects-particularly during nocturnal rest-are limited. This study aimed to investigate the impact of moderate alcohol intake on nocturnal resting heart rate (HR) and sleep parameters using continuous smartwatch-based monitoring in healthy individuals. <b>Methods:</b> In this prospective observational study, 40 healthy adults (63% female, mean age of 30.5 years) underwent a structured 9-day smartwatch monitoring period. The protocol included three alcohol-free baseline days, three consecutive evenings with moderate alcohol consumption (40 g/day for women, 60 g/day for men), and three post-exposure days. Continuous data on HR, sleep stages, nocturnal awakenings, and physical activity were recorded. Subjective sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI) at baseline. The primary endpoint was the change in the average nocturnal resting HR. Secondary outcomes included sleep parameters and activity levels. <b>Results:</b> Alcohol consumption led to a statistically significant increase in nocturnal resting HR from 63.6 ± 9.2 bpm at baseline to 66.6 ± 9.0 bpm during exposure (<i>p</i> < 0.001), with rapid normalization during the post-exposure phase (64.9 ± 9.3 bpm). No significant changes were observed in objective sleep architecture or daytime activity. Despite stable sleep structure, participants reported reduced subjective sleep quality under alcohol exposure, suggesting a potential link to the elevated HR. <b>Conclusions:</b> Even moderate alcohol intake transiently elevates nocturnal resting HR without affecting sleep architecture, likely impairing physiological recovery. These findings underscore the underestimated cardiovascular impact of alcohol and warrant further research in larger and more diverse populations.