New research shows that even a few drinks can disrupt your heart’s nighttime recovery, smartwatches reveal the hidden cardiovascular cost, even when your sleep patterns look normal.
Study: The Impact of Alcohol on Sleep Physiology: A Prospective Observational Study on Nocturnal Resting Heart Rate Using Smartwatch Technology. Image Credit: Mike_shots / Shutterstock
In a recent article published in the journal Nutrients, researchers at Ludwig Maximilian University of Munich, Germany, investigated the impact of moderate alcohol consumption on sleep parameters and nocturnal resting heart rate (HR) in healthy adults, as measured through continuous monitoring using smartwatches.
They found that consuming moderate amounts of alcohol temporarily increased nocturnal resting HR but did not alter the objective sleep architecture. The participants also reported that when they drank alcohol, their perceived sleep quality worsened.
Background
Alcohol consumption has been studied in detail to understand its impacts on sleep and cardiovascular health.
While scientists initially believed that moderate drinking offered some benefits for heart health, these beliefs were subsequently challenged. New research demonstrates that even low levels of alcohol consumption can increase the risk of developing cancer or dying, especially for women.
Today, the World Health Organization does not consider any alcohol intake level to be safe. However, while alcohol is known to disrupt cardiovascular regulation and sleep recovery, few real-world analyses demonstrate these effects.
Nighttime is typically characterized by parasympathetic nervous system activity, facilitating bodily recovery. Disruptions, such as elevated resting heart rate, are linked to worse sleep quality and increased cardiovascular risks. Alcohol acutely activates the sympathetic nervous system, raising HR and reducing HR variability.
Prior studies demonstrated that alcohol could increase HR for hours after intake, but much of the existing data comes from lab settings or unvalidated commercial devices.
Although alcohol is believed to worsen sleep, objective studies often show minimal changes in total sleep time or sleep phases, except for a modest reduction in rapid eye movement (REM) sleep. However, many wearable devices, including the one used in this study, are not able to reliably assess REM sleep, so subtle changes in REM may go undetected.
The subjective feeling of poorer sleep may be due to physiological dysregulation, such as elevated heart rate (HR), rather than major changes in sleep architecture; however, further research is needed to confirm this hypothesis. Additionally, the paper notes that subjective reports of poorer sleep quality could be influenced in part by psychological or expectation effects (placebo or nocebo effects) related to alcohol consumption.
About the study
In this study, researchers evaluated the impact of alcohol on nocturnal heart rate (HR) and sleep in real-world settings using continuous wearable monitoring. A prospective observational study was conducted in Germany, including 40 healthy adults, from July 2024 to January 2025.
Participants wore smartwatches to continuously monitor sleep parameters, heart rate, and activity over a nine-day period: three alcohol-free baseline days, three alcohol-exposure days (60 g/day for men and 40 g/day for women), and three post-exposure days.
The alcohol type was the participant’s choice, but strict alcohol abstinence was required during the baseline period and after exposure. Compliance was ensured through daily logs of physical activity and beverage consumption. Subjective sleep quality was evaluated with the Pittsburgh Sleep Quality Index (PSQI) and other sleep-related questionnaires before and after alcohol exposure.
The primary outcome was the change in average nocturnal resting HR. Secondary outcomes included changes in sleep stages, nocturnal awakenings, physical activity, and subjective sleep quality.
Data analysis involved paired t-tests and one-way analysis of variance (ANOVA) with multiple comparisons for secondary outcomes. Fisher’s test was used for contingency tables.
Findings
Forty healthy adults, with an average age of 30.5 years and a body mass index (BMI) of 25.2 kg/m², participated. The group consisted of 63% females. Half consumed alcohol regularly, mainly beer (53%) or wine (48%). On average, subjective sleep quality was moderate, with 50% reporting moderate sleep issues at baseline.
Alcohol exposure worsened perceived sleep quality for 45% of participants, mainly through increased awakenings and less restful sleep, though sleep initiation was unaffected. Objective smartwatch-based sleep monitoring showed no significant changes in light or deep sleep, sleep duration, or awakenings across phases. As noted above, the device used in this study was unable to measure REM sleep, and therefore, potential effects on REM sleep stages were not assessed.
Physical activity remained stable throughout. The main finding was a significant three bpm increase in nocturnal resting heart rate during alcohol exposure (from 63.6 to 66.6 beats per minute (bpm)), which returned to baseline after alcohol cessation. While a 3 bpm increase may seem modest, the study notes that previous research has linked each 10 bpm rise in nighttime HR to a 10% increase in all-cause and cardiovascular mortality. Thus, even such a small change may reflect a clinically relevant autonomic imbalance.
Subgroup analyses suggested stronger HR effects in women, individuals with a BMI less than 25 kg/m², and smokers. No significant influence of beverage type or regular physical activity on outcomes was observed.
Conclusions
This study demonstrated that even low-to-moderate alcohol intake resulted in a reversible three-bpm increase in nocturnal heart rate, without significantly altering objective sleep architecture; however, subjective sleep quality declined. The rise in HR likely reflects autonomic imbalance, potentially driven by increased sympathetic activity and reduced parasympathetic tone. Possible mechanisms discussed in the paper include alcohol's vasodilatory effect leading to sympathetic activation, direct effects on heart rate (e.g., via calcium channels), increased levels of stress hormones like adrenaline and cortisol, and thermoregulatory or inflammatory stress responses. This imbalance could potentially stress cardiovascular health even in healthy individuals.
Strengths include real-world continuous monitoring using wearable technology. However, the analysis was limited by the small sample size, reliance on consumer-grade devices (which may miss subtle REM sleep changes, as REM was not measured in this study), and focusing only on short-term effects. The study also acknowledges that subjective perceptions of sleep quality may be influenced by participants’ expectations about the effects of alcohol. Results may not generalize to people with chronic illnesses.
Overall, findings suggest that even modest alcohol intake affects cardiovascular regulation during sleep, supporting public health advice to limit alcohol, especially among those with cardiovascular risks. Further large-scale studies are recommended to explore the long-term impacts of alcohol consumption on sleep.
Journal reference:
- The Impact of Alcohol on Sleep Physiology: A Prospective Observational Study on Nocturnal Resting Heart Rate Using Smartwatch Technology. Strüven, A., Schlichtiger, J., Hoppe, J.M., Thiessen, I., Brunner, S., Stremmel, C. Nutrients (2025). DOI: 10.3390/nu17091470, https://www.mdpi.com/2072-6643/17/9/1470