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Afternoon naps may lower heart attack and stroke risk

Wednesday 11 September 2019

"Taking afternoon naps linked to healthy heart," reports The Times. A study carried out in Switzerland found that people who had 1 or 2 afternoon naps a week were less likely to have a heart attack or stroke, compared with people who did not nap. However, having more than 2 naps a week was not linked to any benefit.

Whether napping during the daytime is healthy or unhealthy is unclear. Some previous studies found a reduced risk of heart and circulation problems, while others found a higher risk. This study of 3,462 Swiss adults aimed to see whether the number of naps a week, and the length of time spent napping, could explain the conflicting results.

While researchers found no link between length of naps and heart or circulation problems, they found that 1 or 2 naps might reduce risks, but having more than 1 or 2 naps did not reduce risk.

Sleeping in the daytime on most days could be a sign of a health problem, such as sleep apnoea, which disrupts night-time sleep. If you're very sleepy during the daytime and need to nap most days, see your GP.

For most people, following healthy living advice – such as keeping active, not smoking, eating a healthy diet and not drinking to excess – is likely to give the best chance of avoiding heart attacks or strokes.

Where did the story come from?

The study was carried out by researchers from the University Hospital of Lausanne in Switzerland. It was funded by GlaxoSmithKline, the Faculty of Biology and Medicine of Lausanne and the Swiss National Science Foundation. It was published in the peer-reviewed medical journal Heart, so is free to read online.

The UK media coverage was reasonably accurate and balanced. Most news reports made the point that this is an observational study so cannot show that naps themselves were responsible for any decrease in stroke or heart attack risk. However, some headlines, such as the Sky News headline that napping "halves your risk of heart attack and stroke", overstate the strength of the evidence.

What kind of research was this?

This was a cohort study. Cohort studies are useful for finding links between factors such as daytime napping and outcomes such as heart attacks and strokes. But they cannot prove that the factors cause the outcomes. Other factors, such as people's overall health and lifestyle, may be involved.

What did the research involve?

Researchers randomly recruited adults from the city of Lausanne in Switzerland, aged 35 to 75. Between April 2009 and September 2012, these people were asked about their sleep habits, afternoon napping, physical activity and medical history.

They also had measurements taken of their height, weight, blood pressure, cholesterol levels and glucose levels. A sub-group was tested for sleep apnoea, a condition that disrupts night-time sleep. They were followed up until May 2014 to April 2017, with an average follow-up time of 5.3 years.

Researchers looked to see whether people who took naps of more or less than 1 hour, or who took naps 1 to 2, 2 to 5, or 6 to 7 times a week had a higher or lower risk of cardiovascular events, such as heart attack and stroke, than people who did not nap.

They adjusted their figures to take account of the following possible confounding factors:

  • age, sex, education level
  • tobacco smoking
  • sedentary behaviour (more than 90% of day spent on low intensity physical activities)
  • body mass index (BMI)
  • sleep duration
  • high blood pressure, high cholesterol or diabetes

They also looked at the effects of sleep apnoea in those who had that measured, and of excessive daytime sleepiness. The researchers based their findings on 3,462 people, once they'd excluded those:

  • lost to follow-up
  • who had a previous history of cardiovascular disease
  • missing information on napping or other important information

What were the basic results?

In the 3,462 people in the study group, there were a total of 155 heart attacks or strokes over 5.3 years. The majority of people in the study (58%) said they had not had a nap in the past week. However, 19% reported 1 or 2 naps, 12% reported 3 to 5 naps and 11% reported 6 to 7 naps.

Those who napped most often were more likely to be older men, less well educated, smokers and with a higher BMI. The study found:

  • 4.6% (93/2014) of people who did not nap had a heart attack or stroke
  • 1.8% (12/667) of people who had 1 to 2 naps had a heart attack or stroke
  • 5.4% (22/411) of people who had 3 to 5 naps had a heart attack or stroke
  • 7.6% (28/370) of people who had 6 to 7 naps had a heart attack or stroke

After taking other potential factors into account, the study found that people who napped once or twice a week had a 48% lower risk of heart attack or stroke (hazard ratio (HR) 0.52, 95% confidence interval (CI) 0.28 to 0.95). Other frequency of naps, and length of naps, had no link to the chances of having a heart attack or stroke.

How did the researchers interpret the results?

The researchers said: "Subjects [people] who nap once or twice per week have a lower risk of incident CVD [cardiovascular disease] events while no association was found for more frequent napping or napping duration."

They added: "Nap frequency may help explain the discrepant findings regarding the association between napping and CVD events."

Conclusion

The study might sound like good news for people who like the occasional snooze after lunch. But factors that affect a person's risk of heart attack or stroke are complicated. This study does not provide enough evidence to say that people should start taking an afternoon nap to avoid having heart attacks or strokes.

There are limitations to the study. The main finding that 1 to 2 naps a week reduce the risk of heart attack or stroke is based on just 12 people. It also relies on people accurately reporting how often they nap, and for how long, as well as how long they sleep at night and a range of lifestyle factors.

Because it's an observational study, we cannot rule out that factors other than napping affected people's chances of having a heart attack or stroke. The researchers tried to account for some of these factors, including age, sex, smoking status and BMI. But there may also be other factors that were not measured, which contribute to the link.

If you want to avoid cardiovascular problems, you’re probably best off following general healthy living advice, such as our top 10 healthy heart tips, which includes advice about eating a healthy, balanced diet and exercising.

Analysis by Bazian
Edited by NHS Website