Study finds that the body’s internal clock impairs nighttime blood pressure upon standing in older adults
- Shaun McGillis
- Aug 27
- 3 min read
Updated: Sep 11
A new study from faculty at the Oregon Institute of Occupational Health Sciences at Oregon Health and Science University uncovered a critical reason why older adults are at significantly higher risk of falls during nighttime hours. The research—“The endogenous circadian system impairs nighttime blood pressure response to active standing in older adults,” is published in the Journal of Physiology, reveals that the body’s internal circadian clock dramatically impairs blood pressure responses when older adults stand up, particularly between 10:30 p.m. and 6:30 a.m.
Key discovery
“What we found was that, compared to midlife adults, older adults have impaired blood pressure response to active standing and that internal body clock-related mechanisms were responsible for the impairment,” said lead author, Oregon Institue of Occupational Health Sciences Associate Professor Saurabh Thosar, Ph.D. “This significantly increases the risk of fainting and falls in older adults.
The study compared 25 healthy adults—19 middle-aged (around 50 years old) and six older adults (around 64-years old)—using a gold standard, five-day laboratory protocol that isolated the effects of the body’s circadian system.
Critical findings
The research team found that older adults showed significant blood pressure drops when standing during nighttime hours. Additionally, blood pressure remained dangerously low for at least three minutes after standing in older adults. Unlike with the younger population, the older adults’ vasculature didn’t adequately compensate for the blood pressure drop, which could result in dangerous health outcomes. Furthermore, the researchers found that the greatest impairment occurred between 10:30 p.m. and 6:30 a.m.--times when older populations frequently wake up, for instance to use the bathroom or because of disturbed sleep.
Research to action
“These changes increase the risk of fainting and falls in older adults,” Thosar said. “When someone gets up at night to use the bathroom, their blood pressure may not recover quickly enough to maintain adequate blood flow to the brain.”
Falls are a leading cause of injury and death among older adults, with nighttime falls being particularly devastating. The inability to maintain blood pressure when standing is an independent predictor of future falls and mortality.
Treatment implications
According to Thosar, the research points to several potential interventions, including moderating medication timing to maintain nighttime blood pressure; using compression stockings during sleep; making safety modifications and exploring treatment strategies that account for circadian timing.
"Our data support the use of better-timed blood pressure medications to maintain nighttime blood pressure in older adults," Thosar noted.
Innovative research methods
The study used a unique "forced desynchrony" protocol conducted in continuous dim light, where participants followed 10 recurring cycles of 2-hour 40-minute sleep periods and wake periods. This allowed researchers to isolate the effects of the circadian system from other factors like sleep, activity, and food intake.
"This is likely the only protocol that allows us to test cardiovascular responses to a postural challenge at night without the confounding effects of sleep, activity, food intake, and temperature," Thosar said.
About the research
The study was conducted at OHSU's Oregon Institute of Occupational Health Sciences and funded by the National Institutes of Health. Dr. Thosar's research group investigates how common behaviors like sleep, postural changes, and physical activity interact with the body's internal clock to affect cardiovascular health in people at increased risk. This paper was co-authored by Professor Steven A. Shea, Director of the Oregon Institute of Occupational Health Sciences.
The research appears in the current issue of The Journal of Physiology.
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