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Nocturnal peak in cardiac baroreflex effectiveness aligns with nocturnal trough in systolic blood pressure in young healthy adults: Possible circadian effects.

Brito L, Jones M, et al. • Physiological reports • 2026

TL;DR

In healthy adults, the nocturnal peak in cardiac baroreflex effectiveness index (BEI) is possibly aligned with the circadian trough in systolic blood pressure, occurring at approximately 1 am and 1:40 am respectively.

Key Findings

Results

Systolic blood pressure exhibited a significant circadian trough at approximately 1:40 am.

Statistical significance was p = 0.02
11 healthy adults (24 ± 2 years; 4 males and 7 females) were studied
BP was measured via spontaneous beat-to-beat finger photoplethysmography
Measurements were taken during a 30-h circadian protocol with five recurring 6-h cycles of 4-h standardized wakefulness and 2-h sleep opportunities

Results

Cardiac baroreflex effectiveness index (BEI) exhibited a significant nocturnal peak at approximately 1 am.

Statistical significance was p = 0.02
The nocturnal peak in BEI closely aligned with the systolic BP trough at ~1:40 am
BEI was assessed from spontaneous beat-to-beat BP and R-R intervals recorded at rest for 10 min during each wakefulness period
Dim light melatonin onset was used as a circadian phase marker

Results

Cardiac baroreflex sensitivity (BRS) showed no significant circadian variation.

BRS was assessed alongside BEI using spontaneous beat-to-beat BP and electrocardiogram-derived R-R intervals
Unlike BEI, BRS did not show a statistically significant pattern across the circadian protocol
This dissociation between BRS and BEI suggests these two measures of baroreflex function capture different aspects of cardiovascular regulation

Results

Vascular endothelial function (VEF) exhibited a significant circadian peak at approximately 10 am.

VEF was assessed as flow-mediated dilation of the brachial artery
The peak in VEF at ~10 am did not align with the nocturnal peaks in BEI or systolic BP trough
This finding indicates that different cardiovascular parameters have distinct circadian timing patterns

Methods

A 30-hour forced desynchrony-style circadian protocol was used to isolate circadian effects from behavioral influences on cardiovascular measures.

The protocol incorporated five recurring, identical 6-h cycles of 4-h standardized wakefulness and 2-h sleep opportunities
Measurements were taken at rest for 10 min during each wakefulness period, yielding five time points per participant
Sample size was 11 healthy adults aged 24 ± 2 years
Dim light melatonin onset served as the circadian phase marker to anchor individual circadian timing

Discussion

Whether the alignment between nocturnal BEI peak and systolic BP trough holds in people with disease or whether shifting one measure would shift the other remains undetermined.

The authors note the study was conducted in young, healthy adults only
The causal directionality between BEI and systolic BP circadian patterns was not established
The authors explicitly state 'It remains to be determined whether shifting one would shift the other in a similar direction, and whether the alignment holds in people with disease'

What This Means

This research suggests that the body's ability to regulate blood pressure through a reflex mechanism called the baroreflex follows a daily (circadian) rhythm. Specifically, in young healthy adults, the baroreflex appears to be most effective around 1 am — the same time that blood pressure naturally dips to its lowest nighttime level. The baroreflex is a feedback system that helps stabilize blood pressure moment-to-moment; this study measured two aspects of it: how strongly it responds (sensitivity) and how often it successfully engages (effectiveness). Only the effectiveness measure, not the sensitivity measure, showed this circadian pattern, suggesting these two aspects of baroreflex function are governed differently over the 24-hour day. To isolate true circadian effects from the influence of daily behaviors like eating, activity, and sleep, the researchers used a specialized protocol where participants cycled through repeated short sleep-wake cycles across 30 hours. This design helps separate what the body's internal clock is doing from what the environment or behavior is causing. The study also found that vascular function in blood vessels peaks around 10 am — a different time than the nighttime baroreflex and blood pressure patterns — indicating that different parts of the cardiovascular system have their own distinct daily rhythms. This research matters because disruptions to normal circadian patterns — such as those experienced by shift workers or people with sleep disorders — may affect the coordination between blood pressure and its regulatory systems. The findings raise questions about whether diseases that impair baroreflex function or blood pressure control also disturb these circadian alignments, and whether interventions timed to the body clock could be beneficial. The authors caution that these results come from a small group of young, healthy individuals, and it is not yet known whether the same patterns apply to older adults or those with cardiovascular conditions.

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Citation

Brito L, Jones M, Chaudhary N, Shea S, Thosar S. (2026). Nocturnal peak in cardiac baroreflex effectiveness aligns with nocturnal trough in systolic blood pressure in young healthy adults: Possible circadian effects.. Physiological reports. https://doi.org/10.14814/phy2.71092

Key Findings

What This Means

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