Once or twice weekly daytime nap linked to lower heart attack/stroke risk

But no such association found for greater frequency or duration of naps

September 9, 2019

Science Daily/BMJ

A daytime nap taken once or twice a week may lower the risk of having a heart attack/stroke, finds research published online in the journal Heart. But no such association emerged for either greater frequency or duration of naps.

The impact of napping on heart health has been hotly contested. Many of the published studies on the topic have failed to consider napping frequency, or focused purely on cardiovascular disease deaths, or compared regular nappers with those not opting for a mini siesta, say the researchers.

In a bid to try and address these issues, they looked at the association between napping frequency and average nap duration and the risk of fatal and non-fatal cardiovascular disease 'events,' such as heart attack, stroke, or heart failure, among 3462 randomly selected residents of Lausanne, Switzerland.

Each participant was aged between 35 and 75, when recruited between 2003 and 2006 to the CoLaus study. This has been looking at the factors behind the development of cardiovascular disease.

Participants' first check-up took place between 2009 and 2012, when information on their sleep and nap patterns in the previous week was collected, and their health was then subsequently monitored for an average of 5 years.

Over half (58%, 2014) of the participants said they didn't nap during the previous week; around one in five (19%, 667) said they took one to two naps; around one in 10 (12%, 411) said they took three to five; while a similar proportion (11%, 370) said they took six to seven.

Frequent nappers (3-7 naps a week) tended to be older, male, smokers, weigh more, and to sleep for longer at night than those who said they didn't nap during the day.

And they reported more daytime sleepiness and more severe obstructive sleep apnea -- a condition in which the walls of the throat relax and narrow during sleep, interrupting normal breathing.

During the monitoring period, there were 155 fatal and non-fatal cardiovascular disease 'events'.

Occasional napping, once to twice weekly, was associated with an almost halving in attack/stroke/heart failure risk (48%) compared with those who didn't nap at all.

This association held true after taking account of potentially influential factors, such as age, and nighttime sleep duration, as well as other cardiovascular disease risks, such as high blood pressure/cholesterol.

And it didn't change after factoring in excessive daytime sleepiness, depression, and regularly sleeping for at least 6 hours a night. Only older age (65+) and severe sleep apnea affected it.

But the 67% heightened cardiovascular risk initially observed for frequent nappers virtually disappeared after taking account of potentially influential factors. And no associations with cardiovascular disease 'events' were found for nap length (from 5 minutes to 1 hour plus).

This is an observational study, and as such, can't establish cause, added to which the information on nap and sleep patterns relied on personal recall. But nap frequency may help to explain the differing conclusions reached by researchers about the impact of napping on heart health, suggest the study authors.

In a linked editorial, Drs Yue Leng and Kristine Yaffe, of the University of California at San Francisco, USA, point out that research in this area is hampered by the absence of a gold standard for defining and measuring naps, making it "premature to conclude on the appropriateness of napping for maintaining optimal heart health."

But they add: "While the exact physiological pathways linking daytime napping to [cardiovascular disease] risk is not clear, [this research] contributes to the ongoing debate on the health implications of napping, and suggests that it might not only be the duration, but also the frequency that matters."

And they conclude: "The study of napping is a challenging but also a promising field with potentially significant public health implications. While there remain more questions than answers, it is time to start unveiling the power of naps for a supercharged heart."

https://www.sciencedaily.com/releases/2019/09/190909193219.htm

To Learn Better, Take a Nap (and Don't Forget to Dream)

April 26, 2010

Science Daily/Beth Israel Deaconess Medical Center

It is by now well established that sleep can be an important tool when it comes to enhancing memory and learning skills. And now, a new study sheds light on the role that dreams play in this important process.

Led by scientists at Beth Israel Deaconess Medical Center (BIDMC), the new findings suggest that dreams may be the sleeping brain's way of telling us that it is hard at work on the process of memory consolidation, integrating our recent experiences to help us with performance-related tasks in the short run and, in the long run, translating this material into information that will have widespread application to our lives. The study is reported in the April 22 On-line issue of Current Biology.

"What's got us really excited, is that after nearly 100 years of debate about the function of dreams, this study tells us that dreams are the brain's way of processing, integrating and really understanding new information," explains senior author Robert Stickgold, PhD, Director of the Center for Sleep and Cognition at BIDMC and Associate Professor of Psychiatry at Harvard Medical School. "Dreams are a clear indication that the sleeping brain is working on memories at multiple levels, including ways that will directly improve performance."

To test this hypothesis, the investigators had 99 subjects spend an hour training on a "virtual maze task," a computer exercise in which they were asked to navigate through and learn the layout of a complex 3D maze with the goal of reaching an endpoint as quickly as possible. Following this initial training, participants were assigned to either take a 90-minute nap or to engage in quiet activities but remain awake. At various times, subjects were also asked to describe what was going through their minds, or in the case of the nappers, what they had been dreaming about. Five hours after the initial exercise, the subjects were retested on the maze task.

The results were striking.

The non-nappers showed no signs of improvement on the second test -- even if they had reported thinking about the maze during their rest period. Similarly, the subjects who napped, but who did not report experiencing any maze-related dreams or thoughts during their sleep period, showed little, if any, improvement. But, the nappers who described dreaming about the task showed dramatic improvement, 10 times more than that shown by those nappers who reported having no maze-related dreams.

"These dreamers described various scenarios -- seeing people at checkpoints in a maze, being lost in a bat cave, or even just hearing the background music from the computer game," explains first author Erin Wamsley, PhD, a postdoctoral fellow at BIDMC and Harvard Medical School. These interpretations suggest that not only was sleep necessary to "consolidate" the information, but that the dreams were an outward reflection that the brain had been busy at work on this very task.

Of particular note, say the authors, the subjects who performed better were not more interested or motivated than the other subjects. But, they say, there was one distinct difference that was noted.

"The subjects who dreamed about the maze had done relatively poorly during training," explains Wamsley. "Our findings suggest that if something is difficult for you, it's more meaningful to you and the sleeping brain therefore focuses on that subject -- it 'knows' you need to work on it to get better, and this seems to be where dreaming can be of most benefit."

Furthermore, this memory processing was dependent on being in a sleeping state. Even when a waking subject "rehearsed and reviewed" the path of the maze in his mind, if he did not sleep, then he did not see any improvement, suggesting that there is something unique about the brain's physiology during sleep that permits this memory processing.

"In fact," says Stickgold, "this may be one of the main goals that led to the evolution of sleep. If you remain awake [following the test] you perform worse on the subsequent task. Your memory actually decays, no matter how much you might think about the maze.

"We're not saying that when you learn something it is dreaming that causes you to remember it," he adds. "Rather, it appears that when you have a new experience it sets in motion a series of parallel events that allow the brain to consolidate and process memories."

Ultimately, say the authors, the sleeping brain seems to be accomplishing two separate functions: While the hippocampus is processing information that is readily understandable (i.e. navigating the maze), at the same time, the brain's higher cortical areas are applying this information to an issue that is more complex and less concrete (i.e. how to navigate through a maze of job application forms).

"Our [nonconscious] brain works on the things that it deems are most important," adds Wamsley. "Every day, we are gathering and encountering tremendous amounts of information and new experiences," she adds. "It would seem that our dreams are asking the question, 'How do I use this information to inform my life?'"

http://www.sciencedaily.com/releases/2010/04/100422153753.htm