Is There a Wrong Way to Take a Midday Nap?

In a culture where siesta is practiced, long nappers tended to be the ones at greater risk of having cardiometabolic conditions, observational data showed.

Among people living in the Spanish region of Murcia, midday naps lasting 30 minutes or longer (versus none) were associated with higher body mass index, higher blood pressure, and a cluster of other conditions associated with heart disease and diabetes.

By contrast, those who had short siestas (i.e., "power naps") did not share these risks and were even less likely to have elevated systolic blood pressure than the no-siesta group, according to Marta Garaulet, PhD, of Brigham and Women's Hospital in Boston and the University of Murcia, and colleagues.

"Although napping is traditionally thought to be a good habit and beneficial to health, this notion has become controversial because of studies that have shown that daytime napping is associated with a greater prevalence of obesity and other metabolic alterations. Here, we hypothesize that siesta duration and different lifestyle factors classically related to obesity may help explain this controversy," the authors wrote in Obesity.

They found that the relationship between long siestas and cardiometabolic risks was partly mediated by later nightly sleep timing and food timing, a large lunch right before the siesta, cigarette smoking, and naps in bed vs a sofa.

Some of these risks may be the result of long naps disrupting cortisol daily rhythms. Alterations in cortisol rhythmicity have been shown to induce circadian disruption leading to insulin resistance, central obesity, and metabolic syndrome (MetS), according to the researchers.

What's more, other research has suggested links between long daytime naps in the elderly and incident Alzheimer's dementia.

"Not all siestas are the same. The length of time, position of sleep, and other specific factors can affect the health outcomes of a nap," said Garaulet in a press release.

Her group had previously shown -- through a Mendelian randomization study on U.K. Biobank participants of European ancestry -- evidence of causal links between more frequent daytime napping and higher blood pressure and waist circumference. The present study affirms that there is at least some significant association between the two in a different population for whom siestas are more culturally embedded.

"We will not be able to conclude causality or directionality from our results. Future longitudinal cohort studies or experimental studies are needed to confirm the relationship between nap duration and the development of obesity and MetS and to test the mechanisms involved," Garaulet's team wrote.

"Many institutions are realizing the benefits of short naps, mostly for work productivity, but also increasingly for general health," said study co-author Frank Scheer, PhD, a neuroscientist and chronobiology researcher also at Brigham, in the press release. "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."

The observational study included 3,275 adult volunteers in Murcia who had no history of cardiometabolic disease and were not taking medication.

Baseline metabolic characteristics were measured in clinic and participants were asked to respond to a survey on siestas that collected information on naps and other lifestyle factors.

Mean age was 40 years, with women making up nearly 80% of the group. Habitual siestas were taken by 35% of the cohort (16% long siestas), with an average four naps per week reported.

The study authors acknowledged that such self-reporting is subject to recall bias and lacked actigraphy for backup.

Moreover, it was possible that some individuals had undiagnosed sleep disorders or subclinical conditions that were related to daytime napping and cardiometabolic health, the team cautioned.

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