- Research suggests that less than six hours of sleep is associated with an increased risk of cognitive impairment and high blood pressure.
- A new study now shows that shorter sleep duration could interact with high blood pressure to increase the risk of poor cognitive function and brain aging.
- Although these results are correlational, they could lead to randomized studies evaluating the efficacy of treatments that modify sleep patterns or help manage blood pressure in preventing or delaying cognitive decline.
While some studies have shown a link between insufficient sleep and the risk of cognitive impairment and dementia, other studies have failed to find a similar association between sleep duration and cognitive function.
A new study published in the
The role of high blood pressure in influencing the impact of sleep duration on cognitive health could explain the mixed results found in previous studies.
The study also paves the way for early identification of individuals at risk of cognitive decline and randomized trials investigating treatments for normalizing sleep patterns and high blood pressure to prevent or delay cognitive decline.
The study’s author, Matthew Pase, PhD, associate professor at Monash University, told Medical News Today:
“The results underscore the importance of having healthy blood pressure levels and prioritizing adequate sleep to maintain a healthy brain into old age. Doctors should be reminded to check patients’ blood pressure levels regularly and manage high blood pressure appropriately. Similarly, the medical world is now starting to appreciate the importance of good sleep, and getting good sleep should be considered part of a healthy lifestyle.”
Shorter sleep duration, besides its association with cognitive decline, is also linked to an increased risk of high blood pressure.
Moreover, studies show that high blood pressure in midlife is independently associated with cognitive impairment and dementia later in life. High blood pressure can cause cerebral small vessel disease, which is associated with an increased risk of stroke and cognitive decline.
Cerebral small vessel disease is a heterogeneous condition involving damage to the small blood vessels in the brain, leading to brain tissue damage and atrophy of the brain structures.
The tissue in the brain can be classified into white matter and
Cerebral small vessel disease can cause lesions in the white matter and a decrease in gray or white matter volume. Gray matter forms the brain’s outermost layer and is involved in several important functions, including cognition, whereas white matter is essential to maintain connectivity between regions of grey matter. White matter damage and a decrease in the volume of gray matter are observed in old age and are associated with cognitive decline.
In the present study, the researchers examined whether hypertension influenced the relationship between sleep duration and cognition. In addition, the researchers also examined the impact of hypertension on the association between sleep duration and imaging markers of white matter damage and brain aging.
The study consisted of 682 individuals over 40 years of age enrolled in the
The researchers collected sleep data using a questionnaire and a home-based sleep study (polysomnographic evaluation). In addition, the researchers measured the daytime blood pressure of the participants at the time of the sleep assessment. Around 3.3 years after the sleep assessment, the participants underwent cognitive assessments and magnetic resonance imaging (MRI) scans to assess changes in brain structure.
The researchers did not find an association between sleep duration and cognitive function or brain imaging markers, except gray matter volume. In the latter case, self-reported short sleep duration was associated with larger gray matter volume.
The researchers then analyzed the impact of sleep duration on cognitive Health after segregating the participants into groups with normal and high blood pressure. They found that sleep duration influenced cognitive function and the levels of brain imaging biomarkers only in individuals with high blood pressure.
Increased brain age, tissue injury with shorter sleep
Specifically, among individuals with high blood pressure, a shorter sleep duration was associated with deficits in executive function, which includes higher-level mental processes involved in planning, reasoning, and decision-making.
Moreover, individuals with high blood pressure and shorter sleep durations also showed higher levels of brain imaging markers for aging and tissue injury. Among individuals with high blood pressure, those with self-reported shorter sleep durations showed higher levels of white matter lesions, whereas those with shorter sleep durations, as measured by the sleep study, showed lower gray matter volumes.
The association between sleep duration and cognitive function or brain imaging markers was absent in individuals with normal blood pressure. In other words, these results suggest that shorter sleep duration interacts with high blood pressure to increase the risk of poor cognitive function and greater brain injury.
One of the study’s strengths was its large sample size. However, due to its observational nature, the study does not establish a causal relationship between sleep duration and cognitive health.
The sleep study was only conducted over a single night, so the data on sleep duration may not represent long-term sleep patterns. Blood pressure decreases by 10% at the time of sleep onset, and shorter sleep duration can eliminate this drop in blood pressure. Blood pressure was collected during the daytime, and it is possible that the impact of sleep patterns on the drop in blood pressure at sleep onset was missed.
Furthermore, Christopher Berg, MD, a board certified cardiologist at MemorialCare Heart and Vascular Institute at Orange Coast Medical Center in Fountain Valley, CA, noted, “The strength of their findings was unimpressive. For instance, they evaluated cognitive function via six tests, only 1 of which showed a significant relationship with sleep duration in those with hypertension.”
“They also evaluated six MRI-based parameters, and again, only one of the six showed an association with sleep duration in those with hypertension. How much those particular parameters meaningfully correlate with their actual cognitive performance or, say, risk of dementia is uncertain as is what extrapolation can be made from these findings,” said Berg.
Lastly, he added that individuals show considerable variation in the daily amount of sleep needed.
“A blanket rule of ‘each person needs x hours of sleep,’ I’m not sure, is supported by the literature and doesn’t seem to be the case in practice. However, this study would support the general recommendation that it is important for each person to get adequate sleep (whatever is the adequate amount ) is important for mental and physical health, and potentially more so in patients with hypertension,” he said.
