If you take a nap, make sure it is under 40 minutes or else your risk of metabolic syndrome can increase, a new study reported.
In this study, the researchers conducted a meta-analysis on 21 observational studies that included 307,237 participants to see how naps and daytime sleepiness affected metabolic syndrome, which is a cluster of health conditions that can increase risk of heart disease, type 2 diabetes and stroke.
"Taking naps is widely prevalent around the world," said Tomohide Yamada, a diabetologist at the University of Tokyo and the lead author of the study. "So, clarifying the relationship between naps and metabolic disease might offer a new strategy of treatment, especially as metabolic disease has been increasing steadily all over the world."
Data on naps and daytime sleepiness were assessed using questions that included "Do you have a problem with sleepiness during the day?" and "Do you sleep during the day?" The researchers then looked at these answers in relation to the patients' history of metabolic syndrome.
The researchers found that people who napped for less than 40 minutes did not have an increased risk of metabolic syndrome. People who napped for less than 30 minutes experienced a slight decline in their risk of metabolic syndrome.
Napping for more than 40 minutes, however, led to an increased risk of metabolic syndrome. People who napped for 90 minutes had a 50 percent increased risk of metabolic syndrome. More specifically, people who napped for more than one hour had a 50 percent increased risk of type 2 diabetes. Similar effects were seen in people who reported feeling sleepy during the day.
The researchers pointed out that this study did not find a link between length of a nap and obesity, which is a risk factor for metabolic disease.
"Sleep is an important component of our healthy lifestyle, as well as diet and exercise," Yamada said. "Short naps might have a beneficial effect on our health, but we don't yet know the strength of that effect or the mechanism by which it works."
This is the third study conducted by Yamada and his team that found a link between long naps and adverse health conditions. In his previous studies, Yamada reported that napping more than one hour was tied to an 82 percent higher risk of heart disease, a 27 percent increased risk of all-cause mortality and a 46 percent increased risk of type 2 diabetes.
This study's findings will be presented at the American College of Cardiology's 65th Annual Scientific Session in April.
