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

Does extra sleep on the weekends repay your sleep debt? No, researchers say

February 28, 2019

Science Daily/Cell Press

Insufficient sleep and untreated sleep disorders put people at increased risk for metabolic problems, including obesity and diabetes. But is extra sleep on the weekends enough to reduce those risks? The short answer, according to new findings is 'no.'

"The key take-home message from this study is that ad libitum weekend recovery or catch-up sleep does not appear to be an effective countermeasure strategy to reverse sleep loss induced disruptions of metabolism," says Kenneth Wright of the University of Colorado Boulder.

People often sleep more on weekends than they do during the week. Yet it wasn't known how returning to an insufficient sleep schedule during the workweek after a weekend of recovery sleep influences a person's metabolic health.

To find out, in the new study, researchers led by Christopher Depner and Wright enlisted healthy young adults. Each participant was randomly assigned to one of three groups. The first had plenty of time to sleep -- 9 hours -- each night for 9 nights. The second had just 5 hours to sleep each night over that same period. Finally, the third slept 5 hours for 5 days followed by a weekend in which they slept as much as they liked before returning to another 2 days of restricted sleep.

In the two sleep-restricted groups, insufficient sleep led to an increase in snacking after dinner and weight gain. During ad libitum weekend recovery sleep in the third group, study participants slept an hour longer on average than they usually would. They also consumed fewer extra calories after dinner than those who got insufficient sleep.

However, when they went back to getting insufficient sleep after the weekend, their circadian body clock was timed later. They also ate more after dinner as their weight continued to rise.

The sleep restriction in the first group of participants was associated with a decrease in insulin sensitivity of about 13 percent. But the group that had a chance to sleep more on the weekend still showed less sensitivity to insulin. The insulin sensitivity of their whole bodies, liver, and muscle decreased by 9 to 27 percent after they got insufficient sleep again, once the weekend was over.

"Our findings show that muscle- and liver-specific insulin sensitivity were worse in subjects who had weekend recovery sleep," Depner says, noting that those metabolic aberrations weren't seen in the people who got less sleep all along. "This finding was not anticipated and further shows that weekend recovery sleep is not likely [to be] an effective sleep-loss countermeasure regarding metabolic health when sleep loss is chronic."

The Sleep Research Society and American Academy of Sleep Medicine recommends 7 or more hours of sleep nightly for adults, to promote optimal health. The new findings add to evidence that insufficient sleep is a risk factor for metabolic disorders. It also shows that catching up on weekends isn't the solution to chronic sleep loss during the week.

Wright says that it's not yet clear whether weekend recovery sleep can be an effective health countermeasure for people who get too little sleep only occasionally -- a night or two per week, perhaps. They hope to explore the fine details of these dynamics in future studies, including the influence of daytime napping and other strategies for getting more Zzzs.

https://www.sciencedaily.com/releases/2019/02/190228113534.htm