Investigators from Brigham and Women’s Hospital have linked longer naps to poorer health outcomes, including higher blood pressure and body mass index. 

The researchers assessed more than 3,000 adults from a Mediterranean population—where midday naps, or siestas, are common—examining the relationship of naps and nap duration with obesity and metabolic syndrome. They found that those who took naps of 30 minutes or longer were more likely to have a higher body mass index, higher blood pressure, and a cluster of other conditions associated with heart disease and diabetes compared to those who didn’t take naps.

However, for those who had short naps, this increased risk for obesity and metabolic alterations was not present. In contrast, short nap-takers were less likely to have elevated systolic blood pressure than those who took no siestas. The findings were published in Obesity.

“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,” says senior author Marta Garaulet, PhD, a visiting professor in the Division of Sleep and Circadian Disorders at Brigham and Women’s Hospital, in a release. “A previous study that we conducted in a large study population in the UK had found that siestas were associated with an increased risk of obesity. We wanted to determine whether this would hold true in a country where siestas are more culturally embedded, in this case, Spain, as well as how the length of time for siestas is related to metabolic health.”

Obesity is a growing health concern affecting over one billion people around the world, according to a release from Brigham and Women’s Hospital. Fat accumulation in the body is connected to how food is digested during metabolic processes. Understanding how lifestyle choices, such as taking naps, affect these metabolic mechanisms could help researchers learn how habits influence health.

The researchers examined data from 3,275 adults in a Mediterranean population, specifically people from the Spanish region of Murcia. Baseline metabolic characteristics were measured for the participants at the University of Murcia, and a survey on naps collected additional details regarding their naps and other lifestyle factors. This resulted in the categories of no naps, shorter than 30 minutes, and longer than 30 minutes.

The research team found that long nap-takers had a higher body mass index and were more likely to have metabolic syndrome than those who did not take naps. Additionally, compared with the no-nap group, the long nap group had higher values of waist circumference, fasting glucose levels, systolic blood pressure, and diastolic blood pressure. The researchers found that long naps were associated with later nightly sleep timing and food timing, with increased energy intake at lunch and cigarette smoking, and with the location of naps (a bed versus a sofa), which may explain the higher risks associated with longer duration naps.

While this is an observational study and it is possible that some factors may be a consequence of obesity and not naps per se, a previous study of the data collected in the UK Biobank pointed to a causal relationship between napping and obesity, particularly with abdominal obesity, the most detrimental form. 

In the current study, the authors found a variety of statistically significant lifestyle factors mediating the association between naps and health measures. The results of the study call for future research to investigate whether a short nap is advantageous over a long one, particularly for individuals with habits such as having delayed meals and sleep schedules, or for those who smoke.

“This study shows the importance of considering siesta length and raises the question of whether short naps may offer unique benefits. Many institutions are realizing the benefits of short naps, mostly for work productivity, but also increasingly for general health. 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,” says co-author Frank Scheer, PhD, a senior neuroscientist and professor in the Medical Chronobiology Program in the Brigham’s Division of Sleep and Circadian Disorders, in a release.

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