Low-dose aspirin taken at bedtime has been proposed as a strategy to lower nighttime blood pressure, but the mechanisms behind this effect remain poorly understood. A new pilot study published in Sleep Advances suggests that sleep itself may be an important piece of the puzzle.
Researchers from UConn School of Medicine, Beth Israel Deaconess Medical Center, and Harvard Medical School investigated whether the cardiovascular effects of bedtime aspirin are mediated through sleep-related pathways. The team enrolled 7 healthy adults (5 women, 2 men; mean age 26 years) in a rigorous within-subject, double-blind, placebo-controlled experiment conducted in an inpatient sleep laboratory.
Each participant completed 2 arms of the study. For 2 weeks at home before each hospital stay, they took either 81 mg of aspirin or a placebo at bedtime. Then came a 4-night hospital protocol: 1 baseline sleep night, 2 nights of experimentally induced sleep disturbance, and 1 recovery night. The experimental sleep disturbance involved delaying sleep onset by 1 hour, 5 forced awakenings of 20 minutes each during the night, and waking participants 1 hour earlier than usual.
The goal was to see whether aspirin’s effects on blood pressure and related physiological systems would differ under conditions of normal sleep versus fragmented, shortened sleep.
What they found
Blood pressure. The study did not find a decrease in blood pressure after 2 weeks of bedtime aspirin, either during undisturbed sleep or during the experimental sleep disturbance. This is a notable null result in a small sample and suggests that any BP effects of low-dose aspirin may depend on factors not captured here.
Renin-angiotensin system. Evening renin levels, a key marker of the renin-angiotensin-aldosterone system (RAAS) that regulates blood pressure, were significantly lower after aspirin compared to placebo (p = .048). This finding points to a potential mechanism: aspirin may reduce the activity of the RAAS during sleep, an effect that could influence blood pressure regulation over longer time scales.
Autonomic nervous system. There was a trend toward decreased 24-hour average heart rate after 2 weeks of aspirin (p = .053) and increased heart rate variability (p = .080). During the sleep disturbance nights, the effect became more pronounced: aspirin was associated with significantly lower 24-hour average heart rate compared to placebo (p < .001). These changes suggest that aspirin may shift autonomic balance toward greater parasympathetic activity, particularly under conditions of sleep stress.
Sleep EEG. Aspirin was associated with longer individual slow waves during the disturbed sleep nights (p = .013), and there was a trend toward greater NREM delta power (p = .061). Slow waves are the hallmark of deep, restorative sleep, and their lengthening under aspirin is intriguing. It may indicate that aspirin enhances the brain’s ability to generate deep sleep even when sleep is fragmented.
Mood and well-being. Participants reported improved subjective mood and well-being after 2 weeks of aspirin, an ancillary finding that warrants further investigation.
Why it matters
This is the first study to directly explore whether sleep acts as a mechanistic factor in the cardiovascular effects of low-dose aspirin. The conventional narrative has been that aspirin lowers nighttime blood pressure directly through anti-inflammatory or antiplatelet pathways. These results suggest a more nuanced picture: aspirin may influence the renin-angiotensin system, autonomic tone, and sleep architecture itself, and these effects may be most visible when the sleep system is under stress.
The fact that heart rate and heart rate variability effects grew stronger during experimental sleep disturbance is particularly noteworthy. It suggests that the benefits of bedtime aspirin may be conditional on sleep quality. For people who already sleep poorly, the cardiovascular effects of aspirin could be different, potentially larger, than for those who sleep well.
Limitations
This is a pilot study with only 7 participants. The small sample size limits the statistical power and means that several interesting trends (HRV, delta power, renin) did not reach conventional significance thresholds. Results should be considered preliminary and hypothesis-generating. Larger studies are needed to confirm and extend these findings.
The participants were young and healthy with normal blood pressure. It remains unknown whether the same effects would appear in older adults, people with hypertension, or those with chronic insomnia or other sleep disorders.
Bottom line
This pilot study does not support the idea that low-dose aspirin taken at bedtime directly lowers blood pressure, at least in young healthy adults over a 2-week period. However, the observed changes in renin, heart rate, heart rate variability, and slow-wave activity suggest that sleep may mediate some of aspirin’s cardiovascular effects. The findings are preliminary but point to a rich area for further research: the intersection of sleep, the renin-angiotensin system, and cardiovascular pharmacology.
If confirmed in larger trials, these results could reshape how clinicians think about chronotherapy for cardiovascular prevention. The timing of medication may matter not just because of circadian rhythms, but because of the complex interplay between drugs and the physiology of sleep itself.
Source
Vazquez M, Yang H, Goldstein M, Haack M, Mullington JM. Is sleep a mechanistic factor in the blood pressure lowering effects of low-dose aspirin taken at bedtime? A pilot study. Sleep Advances. 2026;7(3):zpag058. doi:10.1093/sleepadvances/zpag058. PMID: 42454167.