Long naps are associated with a higher risk of obesity, and shorter naps with a reduced risk of high blood pressure.
Are siestas a secret weapon for better health? The question has sparked conflicting opinions among scientists for decades, but one thing is certain: midday naps affect how our bodies function.
In a recent study published in the scientific journal Obesity, a team of Spanish scientists delved into the issue of napping. Their findings shed new light on the relationship between nap duration and location and several metabolic markers, including obesity.
The survey was conducted with more than 3,000 Spaniards from Murcia.
Those who took long naps – more than 30 minutes – were found to have a 2% higher body mass index – a measure of body weight relative to height – than non-sleepers.
They also had a 23% higher risk of obesity and a 40% higher risk of metabolic syndrome, a group of medical conditions that increase the risk of developing cardiovascular disease.
On the other hand, people who took short naps – less than 30 minutes – had a 21% reduced risk of high blood pressure.
“Long naps are associated with increases in metabolic syndrome body mass index, triglycerides, glucose and blood pressure,” said Marta Garaulet, study author and professor of physiology at the University of Murcia, Spain.
“In contrast, when the nap is short, we see that it’s associated with a reduction in the likelihood of high blood pressure, so in a sense, the nap becomes protective.”
Learning concluded that nap duration should be considered “relevant to obesity,” but the results only point to “associations,” Garaulet clarified, not formal cause and effect.
In other words, the researchers made “relevant” associations between people who, for example, take long naps and have a higher risk of obesity, but this does not necessarily mean that these people are overweight because they take long naps. Nor do they take long naps because of their weight.
Culture and a nap
Last year, Garaulet led another UK Biobank study of 450,000 people and found 127 genetic variants associated with napping: “the higher the napping genetics, the higher the frequency of napping,” Garaulet told Euronews Next, ” which would help explain why some people are unable to take a nap.”
The English Study — unlike the Spanish study — used a statistical technique used in genetic research to examine causal relationships between risk factors and health outcomes, called Mendelian randomization. The technique allowed Garaulet’s team to pinpoint “potential causal relationships between more frequent daytime sleepiness and higher blood pressure and waist circumference.”
The Spanish findings are less conclusive because they did not use the statistical technique. They do, however, offer new insights into napping.
The British study was conducted among a population with an average age of 60 “and where napping is not a habit of this culture,” the Spanish scientist said. So she was curious to see what happened in a sample of younger people with fewer illnesses, but also in a country with a solid siesta culture and high temperatures.
The heat was relevant because previous studies have shown that siesta genes are activated by heat.
“Summer temperatures activate the PER3 gene, which is the clock gene that initiates naps,” Garolet said, which would explain why there is a greater tendency for midday naps in the Mediterranean than in Scandinavian countries.
Some people don’t have the genetics for siesta, she explained, “but if you do, then that siesta gene can be activated in warmer areas and you’ll be sleepy during the day.”
The Spanish conclusions refined those obtained by the English bank, and Garaulet was not only able to assess the finer aspects of daytime sleep episodes – in particular how the duration of the siesta affected the health of the subjects being evaluated – but also where people sleep affected the health benefits.
“There is a positive association between short naps and improved blood pressure, especially if you sleep in an armchair or on the sofa rather than lying in bed,” Garole said.
It appears that humans are not meant to have large postural changes throughout the day, as this can raise blood pressure, she explained.
Consistent with her findings linking obesity to long naps, Garolett, who is a visiting professor at Harvard, recently published another study that concluded that people who take long naps are more likely to have an altered rhythm of an enzyme called lipase, which plays a crucial role in the digestion and metabolism of dietary fats.
Naps make better workers
Garolet said understanding the science behind napping could help recommend new methodologies to improve employee performance.
Previous studies have found that short naps are associated with improved working memory as well as improved productivity and alertness, particularly in sleep-deprived subjects, but the long-term effects of habitual napping on chronic disease risk remain controversial.
“That’s why this is a topic of interest, it will help to see if naps should be recommended to get all these benefits in the workplace,” Garole said, “but more research is needed.”
To get conclusive results regarding the metabolic effects of napping, scientists need to conduct randomized crossover trials, Garolet added, which involves conducting experiments in which the same individuals are placed to nap but also abstain from it.
“The problem with these studies is that they can only be done in the short term, so it’s possible to look at the acute effects of napping, but not its effect on overall health.”
Acute effects refer to the short-term changes or responses observed after a specific intervention or exposure, such as improved memory in the case of a short nap.
To draw conclusions about metabolic risk or obesity, researchers need many months with the same subjects, “and it’s not possible to put a person who never naps or doesn’t have the genetics to nap, to nap every day, or to ( there are) those who nap, not to nap for six months,” she said.
But while conducting randomized crossover trials can be challenging, previous long-term studies have provided evidence of the benefits of siesta for our health. Back in 2007 a study conducted by the Harvard School of Public Health suggest that napping contributes to the lower rates of heart disease seen in Mediterranean countries.
The study followed more than 23,000 people for six years and found that regular napping could reduce deaths from cardiovascular disease by as much as 37%, providing a benefit of the same magnitude as that associated with lowering cholesterol, healthy eating, or exercise.
Modern lifestyles have greatly affected the frequency, duration and timing of sleep episodes, and although nap research may not provide conclusive evidence, there is a vast amount of scientific literature supporting the idea that nothing is more vital to our health , happiness, and productivity than a good night’s sleep.