Many believe that lying down for a snooze is a harmless activity. But today, scientists show that drifting off for more than one hour could be risky. The study is presented at ESC Congress 2020.
"Daytime napping is common all over the world and is generally considered a healthy habit," said study author Dr. Zhe Pan of Guangzhou Medical University, China. "A common view is that napping improves performance and counteracts the negative consequences of 'sleep debt'. Our study challenges these widely held opinions."
Previous research on the link between daytime naps and death or cardiovascular disease has produced conflicting results. In addition, it did not account for the duration of night-time sleep.
This study summarised the available evidence to assess the relationship between napping and the risks of all-cause death and cardiovascular disease. A total of 313,651 participants from more than 20 studies were included in the analysis. Some 39% of participants took naps.
The analysis found that long naps (more than 60 mins) were associated with a 30% greater risk of all-cause death and 34% higher likelihood of cardiovascular disease compared to no napping. When night-time sleep was taken into account, long naps were linked with an elevated risk of death only in those who slept more than six hours per night.
Overall, naps of any length were linked with a 19% elevated risk of death. The connection was more pronounced in women, who had a 22% greater likelihood of death with napping compared to no napping, and older participants, whose risk rose by 17% with naps.
Short naps (less than 60 minutes) were not risky for developing cardiovascular disease. Dr. Pan said: "The results suggest that shorter naps (especially those less than 30 to 45 minutes) might improve heart health in people who sleep insufficiently at night."
The reasons why napping affects the body are still uncertain, said Dr. Pan, but some studies have suggested that long snoozes are linked with higher levels of inflammation, which is risky for heart health and longevity. Other research has connected napping with high blood pressure, diabetes, and poor overall physical health.
He concluded: "If you want to take a siesta, our study indicates it's safest to keep it under an hour. For those of us not in the habit of a daytime slumber, there is no convincing evidence to start."
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