Napping can be a quick way to get an energy boost during the day, but not all naps are the same. According to a new study published in Obesity, people who take long naps may be at a greater risk of cardiometabolic conditions, including obesity and high blood pressure, than those who take short naps.
For the study, researchers analyzed data from 3,275 adults living in Murcia, Spain, who had no history of cardiometabolic disease and were not on any medications. The mean age was 40 years, and 80% of the participants were women.
The researchers measured participants' baseline metabolic characteristics at a clinic. The participants also completed a survey that gathered information on siestas, or afternoon naps, and other lifestyle factors.
Overall, 35% of participants reported taking regular siestas, averaging four naps per week. Of this group, 16% said they took long siestas that lasted 30 minutes or more.
According to the researchers, napping for 30 minutes or longer was associated with several cardiometabolic conditions, including higher body mass index, higher blood pressure, and certain conditions associated with heart disease and diabetes.
In comparison, shorter naps were not associated with any of these cardiometabolic conditions. And those who took shorter naps were at even less risk of elevated systolic blood pressure than those who took no naps at all.
However, the researchers also found that the association between long siestas and cardiometabolic risks was partially mediated by certain factors, such as eating and sleeping later in the night, having a large lunch right before a nap, smoking cigarettes, and napping in a bed vs. a sofa.
Some of the cardiometabolic risks associated with long naps may be due to disruptions in cortisol daily rhythms, the researchers said. Changes in cortisol rhythms have been shown to cause circadian disruption, which then lead to insulin resistance, central obesity, and metabolic syndrome (MetS).
According to Marta Garaulet, one of the study's authors from Brigham and Women's Hospital, the findings show that "[n]ot all siestas are the same. The length of time, position of sleep, and other specific factors can affect the health outcomes of a nap."
Previously, Garaulet and her colleagues found an association between more frequent daytime napping and waist circumference and higher blood pressure among U.K. Biobank participants who were of European descent. This current study provides more evidence that there is at least some association between long naps and cardiometabolic conditions, especially in a different population where siestas are more culturally embedded.
However, the researchers said they are not able "to conclude causality or directionality" from the findings and more studies, including longitudinal cohort or experimental studies, will be needed to confirm a relationship between nap duration and cardiometabolic conditions.
They also noted that it's possible some cardiometabolic conditions may be a consequence of obesity rather than a nap. Future research will be necessary to determine whether a short nap is actually more beneficial than a long one.
"Many institutions are realizing the benefits of short naps, mostly for work productivity, but also increasingly for general health," said Frank Scheer, a neuroscientist and chronobiology researcher Brigham and Women's Hospital and another study author. "If future studies further substantiate the advantages of shorter siestas, I think that that could be the driving force behind the uncovering of optimal nap durations, and a cultural shift in the recognition of the long-term health effects and productivity increases that can amount from this lifestyle behavior." (Lou, MedPage Today, 4/26; Krištopaitytė, Health News, 5/3; Vizmanos et al., Obesity, 4/26)
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