Long naps are associated with a higher risk of obesity, and shorters ones with reduced risk of high blood pressure.
ADVERTISEMENTAre siestas a secret weapon for better health? The question has sparked conflicting opinions among scientists for decades, but one thing is certain: the midday snooze affects how our bodies function.
In a recent study published in the scientific journal Obesity, a team of Spanish scientists delved into the napping question. Their findings shed new light on the connection between the duration - and location - of naps and several metabolic markers, including obesity.
The study was conducted with more than 3,000 Spaniards from Murcia.
It found that those who took long naps - more than 30 minutes - had a 2 per cent higher body mass index - a measure of body weight in relation to height - than non-sleepers.
They also had a 23 per cent higher risk of obesity and a 40 per cent higher risk of metabolic syndrome - a group of medical conditions that increase the risk of developing cardiovascular disease.
On the other hand, people who napped for short stretches - fewer than 30 minutes - had a 21 per cent reduced risk of high blood pressure.
"Long naps are associated with an increase in the body mass index of metabolic syndrome, triglycerides, glucose and blood pressure,” said Marta Garaulet, author of the study and Professor of Physiology at the University of Murcia, Spain.
“In contrast, when the nap is short, we see it associated with a decrease in the probability of having high blood pressure, so in a way, the nap becomes protective".
The study concluded that nap duration should be considered as “relevant in obesity,” but the results only point to "associations", clarified Garaulet, and not a formal cause and effect.
In other words, the researchers have made “relevant” associations between people who, for example, take long naps and have a higher risk of obesity, but that does not necessarily mean these people are overweight because they are taking long naps. Nor that they are taking long naps due to their weight.
Culture and napping
Last year Garaulet led another study in the UK Biobank with 450,000 people and found 127 genetic variants associated with napping: "the higher genetics of napping, the higher frequency of naps," Garaulet told Euronews Next, "which would help explain why some people are incapable of napping".
The English study - unlike the Spanish study - used a statistical technique used in genetic research to investigate causal relationships between risk factors and health outcomes called Mendelian randomisation. The technique allowed Garaulet’s team to point out “potential causal links between more frequent daytime napping and higher blood pressure and waist circumference.”
The Spanish findings are less conclusive because they did not use the statistical technique. However, they do offer new insights into napping.
The British study was carried out in a population with a median age of 60 years old "and where napping is not a habit of that culture," said the Spanish scientist. That is why she was curious to see what happened in a sample of younger people with fewer diseases, but also in a country where there is a solid siesta culture and hot 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, nap-initiating gene,” said Garaulet, which would explain why in the Mediterranean there is more of a tendency to nap at midday than in Nordic countries.
Some people don't have siesta genetics, she explained, “however, if you do, then this siesta gene might get activated in warmer areas, and you’ll feel like sleeping during the day".
The Spanish conclusions refined those obtained from the English bank, and Garaulet was not only able to assess the finer aspects of daytime sleep episodes - notably how the length of the siesta had an influence on the health of the evaluated subjects - but also that where people slept influenced the health benefits.
ADVERTISEMENT"There is a positive association between short naps and improved blood pressure, especially if you sleep in an armchair or on the sofa, not lying in bed," Garaulet said.
It seems that humans are not meant to have major postural changes throughout the day, as this can increase blood pressure, she explained.
In line with her findings linking obesity to long naps, Garaulet, 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 in an enzyme called lipase, which plays a crucial role in the digestion and metabolism of dietary fats.
Naps make better workers
Garaulet said that understanding the science behind naps 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 performance and alertness, notably in sleep-deprived subjects, but the long-term effects of habitual napping on chronic disease risk remain controversial.
ADVERTISEMENT“This is why it is a topic of interest, it will help to see whether or not a nap should be recommended to obtain all these benefits at work,” said Garaulet, “but more research is needed.”
To achieve conclusive results regarding the metabolic effects of napping, scientists must conduct randomised crossover studies, added Garaulet, which entails doing experiments where the same individuals are put to nap but also abstain from it.
"The problem with these studies is that they can only be done over the short term, so it is possible to look at the acute effects of napping, but not its effect on the 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 short napping.
To determine conclusions on metabolic risk or obesity, researchers need many months with the same subjects, “and it is not possible to put a person who never naps or does not have the genetics to nap, to nap every day or to (have) those who do nap, not to nap for six months," she said.
ADVERTISEMENTBut while conducting randomised crossover studies can be challenging, previous long-term studies have provided evidence of the benefits of siestas for our health. Back in 2007, a study conducted by the Harvard School of Public Health suggested that napping contributed to the lower rates of heart disease observed in Mediterranean countries.
The study followed more than 23,000 people for six years and showed that regular napping can cut deaths from heart disease by as much as 37 per cent, providing a benefit in the same order of magnitude as that linked to lowering cholesterol, eating a healthy diet, or exercising.
Modern lifestyles have significantly influenced the frequency, duration, and timing of sleep episodes, and while the research on naps may not provide conclusive evidence, there is an overwhelming body of scientific literature supporting the notion that nothing is more vital for our health, happiness, and productivity than a good night's sleep.
