Original Article | Medical News Today

• Researchers report that better sleep may translate into a lower risk of cardiovascular disease.

• They add that consistent and healthy sleep patterns can improve a person’s overall well-being.
• Experts say people having trouble sleeping should rethink pre-sleep activities and avoid stimulation before bedtime.

A studyTrusted Source published in the journal JAMA Network Open reports that midlife and older adults with healthy sleep habits have a better chance of avoiding cardiovascular disease.

Researchers used data collected between 2008 and 2018 from the Dongfeng-Tongji cohortTrusted Source, an ongoing, prospective study in Shiyan, China.

The research team looked at 15,306 individuals with an average age of 66 years with 58% being female and 42% being male. The researchers reported that 5,474 (36%) people had persistent unfavorable sleep patterns and 3,946 (26%) had persistent favorable sleep patterns.

The researchers established that 3,669 members of the study group had documented cases of cardiovascular disease during that period, including 2,986 cases of coronary heart disease and 683 cases of stroke over a mean follow-up period of nearly 5 years.

Compared to people with persistent unfavorable sleep patterns, those with persistent favorable sleep patterns had a significantly lower risk of new onset cardiovascular disease, coronary heart disease, and stroke during the follow-up period.

Researchers said the genetic risk for cardiovascular disease didn’t modify these associations.

“However, sleep pattern changes and genetic risk were jointly associated with the [coronary heart disease] and stroke risk in a dose-dependent manner,” the study authors wrote.

Healthy sleep and heart disease risk 

The five-year patterns in the study were determined by bedtime, sleep duration, sleep quality, and midday napping as well as polygenic risk scores for coronary heart disease and stroke.

The participants included people with complete sleep information at the baseline survey from 2008 to 2010 and the first follow-up survey in 2013. Subjects with no history of cardiovascular disease or cancer were prospectively assessed from 2013 to 2018. Scientists performed their statistical analysis in November 2023.

The authors pointed out cardiovascular disease “is a major cause of morbidity and mortality worldwide. In 2019, cardiovascular deaths accounted for approximately one-third of all deaths globally, including more than 40% of deaths in China.

The researchers also said that as the cardiovascular disease burden keeps rising in nearly every country, research identifying modifiable risk factors for prevention of serious heart disease is urgent.

The team acknowledged previous studies have shown an association of sleep with cardiovascular health.

However, the researchers said most of those studies used only a single measurement, which might not adequately reflect the association of overall sleep with cardiovascular disease as sleep habits may change over time.

Researchers cited one studyTrusted Source of 9,309 participants living in Europe that indicated that maintaining healthy sleep patterns over a 2-year to 5-year period was associated with a lower risk of cardiovascular disease and coronary heart disease but not stroke.

However, they noted that the research looked at people in midlife who typically adjusted their sleep patterns around work schedules.

Lifestyle and genetics also factors in heart health 

The study authors noted that more research on older, retired people with more natural sleep patterns is still necessary.

The researchers added that lifestyle and genetic factors are also associated with cardiovascular disease, and previous research has shown people with healthy lifestyles had a lower risk of coronary heart disease and stroke, even among those at high genetic risk.

“To fill the evidence gap, we collected sleep information at two time points approximately five years apart and prospectively explored the long-term outcomes of changes in sleep patterns on the subsequent incidence of [cardiovascular disease] outcomes among middle-aged and older Chinese retirees,” the study authors wrote. “We further investigated how the five-year changes in sleep patterns interact and combine with [cardiovascular disease]-related genetic variants for the risk of [cardiovascular disease] outcome.”

Chelsey Borson, a sleep expert and founder of baby sleep consulting service Luna Leaps who was not involved in the study, told Medical News Today that sleep has profound impacts on overall health, including heart health.

“The link between adequate sleep and heart health is increasingly recognized as vital. Sleep serves as a period of recovery and repair for the heart, reducing stress and inflammation, major risk factors for heart disease,” Borson explained. “It’s not an entirely new idea, but the depth of understanding has deepened significantly in recent years as research has advanced.”

Borson said studies show people getting fewer than seven hours of sleep per night tend to have higher risks of developing cardiovascular issues such as hypertension, coronary artery disease, and myocardial infarction, which “underscores sleep’s role in regulating blood pressure, heart rate, and cardiovascular stability.”

Original Article | Sleep Review Magazine

A new study proposes a mechanism that determines which memories are tagged as important enough to linger in the brain until sleep makes them permanent.

Summary: A recent study led by NYU Grossman School of Medicine researchers has identified a mechanism through which the brain selects certain memories to become permanent during sleep. Focusing on the hippocampus’s neurons, the study found that “sharp wave-ripples,” brief bursts of intense neuron activity, play a crucial role in this selection process. Memories followed by these ripples during the day are more likely to be replayed and solidified in sleep.

Key takeaways: 

• The study identified “sharp wave-ripples” in the hippocampus as crucial for selecting which daytime memories become permanent during sleep.
• Daytime events followed by five to 20 sharp wave-ripples are more likely to be consolidated into long-term memories.
• This process involves the near-simultaneous firing of 15% of hippocampal neurons, encoding complex information within milliseconds.

Neuroscientists have established in recent decades the idea that some of each day’s experiences are converted by the brain into permanent memories during sleep the same night. 

Now, a new study proposes a mechanism that determines which memories are tagged as important enough to linger in the brain until sleep makes them permanent.

Led by researchers from NYU Grossman School of Medicine, the study revolves around brain cells called neurons that “fire”—or bring about swings in the balance of their positive and negative charges—to transmit electrical signals that encode memories. Large groups of neurons in a brain region called the hippocampus fire together in rhythmic cycles, creating sequences of signals within milliseconds of each other that can encode complex information.

Called “sharp wave-ripples,” these “shouts” to the rest of the brain represent the near-simultaneous firing of 15% of hippocampal neurons and are named for the shape they take when their activity is captured by electrodes and recorded on a graph. 

While past studies had linked ripples with memory formation during sleep, the new study, published in Science, found that daytime events followed immediately by five to 20 sharp wave-ripples are replayed more during sleep and so consolidated into permanent memories. Events followed by very few or no sharp wave-ripples failed to form lasting memories.

“Our study finds that sharp wave-ripples are the physiological mechanism used by the brain to ‘decide’ what to keep and what to discard,” says senior study author György Buzsáki, MD, PhD, the Biggs Professor of Neuroscience in the Department of Neuroscience and Physiology at NYU Langone Health, in a release.

Walk and Pause

The new study is based on a known pattern: Mammals including humans experience the world for a few moments, then pause, then experience a little more, then pause again. After we pay attention to something, say the study authors, brain computation often switches into an “idle” re-assessment mode. Such momentary pauses occur throughout the day, but the longest idling periods occur during sleep.  

Buzsaki and colleagues had previously established that no sharp wave-ripples occur as we actively explore sensory information or move, but only during the idle pauses before or after. The current study found that sharp wave-ripples represent the natural tagging mechanism during such pauses after waking experiences, with the tagged neuronal patterns reactivated during post-task sleep.

Importantly, sharp wave-ripples are known to be made up the firing of hippocampal “place cells” in a specific order that encodes every room we enter and each arm of a maze entered by a mouse. For memories that are remembered, those same cells fire at high speed, as we sleep, “playing back the recorded event thousands times per night.” The process strengthens the connections between the cells involved.

Tracing Memory Formation

For the current study, successive maze runs by study mice were tracked via electrodes by populations of hippocampal cells that constantly changed over time despite recording very similar experiences. This revealed for the first time the maze runs during which ripples occurred during waking pauses and then were replayed during sleep.

Sharp wave-ripples were typically recorded when a mouse paused to enjoy a sugary treat after each maze run. The consumption of the reward, say the authors, prepared the brain to switch from an exploratory to an idle pattern so that sharp wave-ripples could occur.

Using dual-sided silicon probes, the research team was able to record up to 500 neurons simultaneously in the hippocampus of animals during maze runs. This in turn created a challenge because data becomes exceedingly complex the more neurons are independently recorded. 

To gain an intuitive understanding of the data, visualize neuronal activity, and form hypotheses, the team successfully reduced the number of dimensions in the data, in some ways like converting a three-dimensional image into a flat one, and without losing the data’s integrity.

“We worked to take the external world out of the equation, and looked at the mechanisms by which the mammalian brain innately and subconsciously tags some memories to become permanent,” says first author Wannan (Winnie) Yang, PhD, a graduate student in Buzsáki’s lab, in a release. “Why such a system evolved is still a mystery, but future research may reveal devices or therapies that can adjust sharp wave-ripples to improve memory, or even lessen recall of traumatic events.”