Blood pressure normally falls while we sleep, but that healthy nighttime decline does not happen in everyone.
A new modelling study suggests that the timing of the kidneys’ daily salt-processing rhythm may help explain why.
Researchers at the University of Waterloo used an integrated computer model of long-term blood pressure regulation to test how daily rhythms in the kidneys, blood vessels, nervous system, hormones and sleep-wake behaviour interact.
The model reproduced the normal pattern in which nighttime blood pressure falls by about 10% to 20% relative to daytime levels.
When the researchers weakened the daily rhythm of kidney sodium transport, the effect on nighttime blood pressure was modest.
But when they delayed the timing of that kidney rhythm by a few hours, the model shifted from a healthy dipping pattern to a non-dipping pattern.
The effect became stronger under higher sodium intake and greater salt sensitivity.
The findings suggest that blood pressure regulation may depend not only on whether the body’s daily rhythms remain intact, but also on whether those rhythms remain correctly aligned with one another.
Blood pressure normally falls during sleep
Blood pressure follows a daily rhythm.
For many healthy people, nighttime blood pressure is approximately 10% to 20% lower than daytime blood pressure.
This pattern is commonly described as nocturnal dipping.
Some people experience a much smaller decline or no meaningful decline at all.
This non-dipping pattern has been associated with cardiovascular and kidney problems, including stroke, left ventricular hypertrophy, progression of chronic kidney disease and increased mortality.
Non-dipping is also more common in several conditions that affect blood pressure regulation, including salt-sensitive hypertension, diabetes, obesity, kidney disease, ageing and sleep disorders.
Several body systems follow their own 24-hour rhythms
Blood pressure is not controlled by a single organ.
The kidneys, blood vessels, nervous system and hormone systems all contribute to regulating blood pressure over the course of a day.
Many of these systems also have circadian rhythms.
The researchers wanted to determine whether the relative timing of those rhythms could influence whether blood pressure falls normally during sleep.
The study used a computer model rather than human participants
The study did not recruit patients or experimentally alter people’s kidney rhythms.
Instead, researcher Anita T. Layton developed an integrated circadian and sleep-wake computational model of long-term blood pressure regulation.
The model incorporated rhythmic changes in renal sympathetic nervous activity, vascular tone, the renin-angiotensin-aldosterone system, kidney tubular sodium transport and behavioural effects associated with sleeping and waking.
This allowed the researcher to change individual components while holding other mechanisms constant.
That type of controlled manipulation would be difficult to perform experimentally in people.
The model first reproduced a healthy dipping pattern
Before testing disruptions, the model was used to reproduce a physiologically realistic healthy blood pressure rhythm.
It generated lower blood pressure at night and greater sodium excretion during the daytime.
This baseline allowed the researcher to examine what happened when the strength or timing of individual rhythms changed.
Weakening the kidney rhythm had only a modest effect
One possibility was that non-dipping blood pressure might occur simply because the kidneys lose their normal daily rhythm.
The simulations did not strongly support that explanation on its own.
Progressively reducing the rhythmic variation in kidney tubular sodium transport shifted more sodium excretion toward nighttime.
However, it produced only modest changes in the extent of blood pressure dipping.
This suggested that the presence or strength of the kidney rhythm was not the whole story.
Changing the timing produced a much larger effect
The result changed when the timing of kidney sodium transport was shifted.
Delaying the tubular sodium transport rhythm shifted sodium excretion toward the nighttime period.
More importantly, the timing change converted the model from a normal dipper phenotype to a non-dipper phenotype even though rhythmic oscillations in the other physiological systems remained intact.
This distinction is central to the study.
The model suggests that a biological rhythm can still be present but become problematic when its timing is out of alignment with the rest of the body’s regulatory systems.
Higher sodium intake amplified the modelled vulnerability
The researcher also tested conditions involving sodium loading.
Higher sodium intake made the model more vulnerable to non-dipping when the kidney sodium transport rhythm was delayed.
Enhanced salt-sensitive sodium reabsorption produced a similar amplification.
This is notable because salt sensitivity is already associated with hypertension and abnormal nighttime blood pressure patterns.
The modelling results therefore provide a possible mechanism linking salt handling, circadian timing and nighttime blood pressure regulation.
Blood vessels and sleep-wake effects remained major drivers
The kidney was not the only important component in the simulations.
Component analyses indicated that daily changes in vascular function and the direct effects of sleeping and waking were dominant determinants of blood pressure dipping.
The intrinsic rhythm of kidney sodium transport played a stronger role in determining when sodium was excreted.
The findings therefore point toward coordination between systems rather than a single kidney mechanism acting in isolation.
Timing may matter as much as whether a rhythm exists
Circadian research often examines whether a biological rhythm becomes weaker or disappears.
This study highlights another possibility.
Different physiological rhythms may remain individually functional while becoming mistimed relative to one another.
In the model, that temporal misalignment was sufficient to disrupt a healthy nighttime blood pressure pattern.
This could help researchers investigate why non-dipping occurs in people whose underlying blood pressure control systems are still active.
The findings do not show that people should change when they consume salt
The study has an important limitation for anyone looking for immediate lifestyle advice.
It was a computational modelling study.
It did not test whether changing the time of salt consumption in people restores normal nighttime blood pressure dipping.
It also did not test whether changing the timing of blood pressure medication would correct the modelled mechanism.
The results should therefore not be used as a reason to independently alter medication schedules or make timing-based treatment decisions.
The proposed mechanism now needs testing in people
Computer models are useful because they allow researchers to isolate mechanisms that are difficult to manipulate separately in living people.
But their predictions depend on the assumptions, equations and physiological relationships built into the model.
The next step is to determine whether measurable shifts in kidney sodium-handling rhythms are associated with non-dipping blood pressure in clinical populations.
Experimental and clinical research would also be needed to establish whether correcting such misalignment improves nighttime blood pressure.
The study offers a new way to think about nighttime hypertension
The main contribution of the study is not a new treatment.
It is a mechanistic hypothesis about how otherwise functioning daily rhythms could become harmful when their timing no longer matches.
In the simulations, simply weakening the kidney’s sodium transport rhythm had relatively little influence on nighttime blood pressure.
Shifting the timing of that rhythm produced a much larger change and converted the model to a non-dipping pattern.
Higher sodium intake and salt sensitivity made that effect stronger.
If future human studies support the mechanism, circadian alignment could become an additional factor for researchers to consider when studying nighttime hypertension.
Source Information
Study Title: Temporal misalignment of renal sodium transport promotes non-dipping blood pressure phenotypes
Author: Anita T. Layton
Journal: PLOS ONE
Published: 13 August 2026
Institution: University of Waterloo, Canada
Method: An integrated circadian and sleep-wake computational model of long-term blood pressure regulation incorporating rhythmic renal sympathetic activity, vascular tone, renin-angiotensin-aldosterone signalling, tubular sodium transport and behavioural sleep-wake effects. The researcher used virtual experiments to alter the strength and timing of individual physiological rhythms and assess their effects on sodium excretion and nighttime blood pressure dipping.
Main finding: Weakening the kidney tubular sodium transport rhythm had only modest effects on blood pressure dipping, while delaying its phase shifted sodium excretion toward nighttime and converted the model from a healthy dipper to a non-dipper phenotype. Sodium loading and increased salt-sensitive sodium reabsorption amplified the effect.
Limitations: This was a computational study rather than a clinical trial or observational human study. The proposed mechanism requires experimental and clinical validation and does not establish that people should change the timing of salt intake or blood pressure medication.
DOI: 10.1371/journal.pone.0355222
