Taking a long siesta might not be so good for you, scientists warn

A veritable institution in some countries, it turns out that naps might not be as beneficial to health as we think. It all depends on the length of the siesta. In fact, US researchers suggest that long naps, lasting more than 30 minutes, could be associated with a higher risk of obesity, high blood pressure and metabolic syndrome.

From memory and concentration to mood, alertness and learning capacity, in theory, the daily siesta seems to have plenty of plus points. But the benefits of napping in the middle of the day could vary in relation to the duration of sleep.

In fact, it is short siestas, sometimes called power naps, that appear to be most beneficial to health, according to a study conducted by researchers at Brigham and Women's Hospital.

They looked at the relationship between nap duration and certain pathologies, examining data from 3,275 adults from the Spanish region of Murcia, where napping is considered at least in the collective imagination -- something of an institution.

Negative health effects

Published in the journal Obesity, the researchers' work focused on measuring participants' baseline metabolic characteristics and then collecting data on their naps and other lifestyle factors.

One goal was to find out whether they napped for more or less than 30 minutes, or not at all.

The scientists' findings suggest that naps longer than 30 minutes considered long siestas increase the risk of obesity, high blood pressure and metabolic syndrome, which translates into physiological symptoms that in turn increase the risk of type 2 diabetes and heart disease.

"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 senior author Marta Garaulet, PhD, a visiting professor in the Division of Sleep and Circadian Disorders at Brigham and Women's Hospital.

"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," she said in a statement.

In detail, the group of scientists observed higher values of waist circumference, fasting blood glucose and blood pressure in participants who took long siestas compared to those who did not nap at all.

Long naps were also associated with later sleep and meal times, higher energy intake at lunchtime, and smoking, factors that may also explain the increased risk of obesity and high blood pressure.

What's the ideal nap length?

The researchers note that short siestas, lasting less than 30 minutes, were not associated with an increased risk of obesity or metabolic alterations.

They add that power naps were beneficial for blood pressure, which was found to be lower in participants who slept for a short while compared to those who did not nap at all.

This conclusion supports the Brigham and Women’s Hospital's advice on napping, which notably recommends limiting naps to 20 or 30 minutes maximum, and not to take a siesta after 3 p.m.

"This study shows the importance of considering siesta length and raises the question 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," said 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.