Most people's blood pressure falls by 10 to 20 per cent while they sleep, giving the heart and blood vessels a chance to recover. But for some people, that nighttime dip never happens. Known as "non-dippers," these individuals face a higher risk of heart disease, stroke, kidney disease and premature death.
Now, researchers at the University of Waterloo have identified a possible reason why.
A new study suggests that even a small mismatch in the timing of how the kidneys process salt may cause blood pressure to remain elevated overnight. The findings offer new insight into a condition that has puzzled researchers for decades.
"Many systems that control blood pressure follow their own 24-hour rhythms, including the kidneys, blood vessels, nervous system and hormones," said Dr. Anita Layton, professor of Applied Mathematics at Waterloo and Canada 150 Research Chair Laureate in Mathematical Biology and Medicine. "What we found is that the timing of these systems' daily rhythm may be just as important as the rhythm itself."
Together, these systems' internal clocks help regulate blood pressure throughout the day and night. Until now, little was known about how differences in timing between these systems might affect cardiovascular health.
Using a sophisticated computer model of the human body, Layton and her team conducted a series of virtual experiments to examine how changes in these biological rhythms influence blood pressure during sleep. The model let researchers adjust individual systems one at a time, something difficult to do in laboratory or clinical studies.
The researchers discovered that weakening the kidney's daily rhythm had only a modest effect on nighttime blood pressure. However, delaying that rhythm by just a few hours was enough to turn a healthy blood-pressure pattern into a potentially harmful non-dipping pattern.
The effect was strongest in people with higher salt intake and in those who are more sensitive to salt, two factors already linked to high blood pressure.
"This is a modelling study, so it does not yet tell people to change when they eat salt or take blood-pressure medication," said Layton. "But it identifies a mechanism that can now be tested experimentally and clinically and may ultimately help us better understand and treat nighttime hypertension and non-dipping blood pressure."
The study, Temporal misalignment of renal sodium transport promotes non-dipping blood pressure phenotypes , was published in PLOS ONE.
