Sleeping in on a day off feels wonderful, especially for those of us who don’t get nearly enough rest during the work week. But are the additional weekend winks worthwhile? Psychologist Torbjorn Akerstedt, director of the Institute for Stress Research at Stockholm University, and his colleagues tried to answer this question in a study published on Wednesday in the Journal of Sleep Research.
Akerstedt and his colleagues have followed more than 38,000 people in Sweden over 13 years, with an emphasis on their sleeping habits on weekends versus weekdays. That look at weekend sleep fills an “overlooked” void in sleep science, Akerstedt said.
In previous sleep studies, people were asked to count their hours of sleep for an average night without distinguishing between work days and days off. Not in the new study. People under 65 who slept five hours or less each night all week did not live as long as those who slept seven hours a night continuously.
But weekend sleepers lived just as long as the well rested. People who slept less than the recommended seven hours of sleep each day of the week but caught an hour or two more on the weekend lived just as long as people who always slept seven hours, the authors reported.
“It appears that the weekend compensation is good,” Akerstedt said, although he cautioned that it was a “preliminary conclusion” of this new research.
Epidemiologists speaking to the Washington Post described the result as a plausible, if not statistically robust, result that deserves more investigation.
Michael Grandner, director of the sleep and health research program at the University of Arizona College of Medicine, who was not involved in this work, warned that sleep is not a financial transaction. We can’t deposit Zzzs over the weekend and expect them to be paid out later.
A superior metaphor, he said, is diet. For the insomniac, sleeping in on a weekend is like eating a salad after a series of hamburger dinners – healthier, safe, but from “one perspective the damage is done”.
In September 1997, thousands upon thousands of Swedes completed 36-page health questionnaires as part of a fundraiser for the Swedish Cancer Society. The study authors followed 38,015 respondents over 13 years to track their death rates. Between 1997 and 2010, 3,234 of these people died, most of them from cancer or heart disease. That’s about six deaths per 1,000 people a year. By comparison, the global death rate in 2010 was nearly eight in 1,000.
The researchers tried to take into account the common gremlins that affect sleep: alcohol consumption, coffee consumption, naps, smoking, shift work, and similar factors, and used statistical methods to control their effects. “The only thing we don’t have under control are latent diseases,” said Akerstedt, referring to diseases that went undetected in a person’s life.
Diane Lauderdale, professor of epidemiology at the University of Chicago, pointed out that this group is not representative of most people, even by 1997 Swedish standards. For example, fewer than average were smokers (people who smoke regularly may not be as eager to attend a cancer society event, she said).
Also not on the research team, Franco Cappuccio, epidemiologist and cardiovascular doctor of the University of Warwick in England, said the study “looks good,” but the authors missed a trick: “a full explanation of the possibility of napping during the day. “The researchers only asked if people napped daily, but did not quantify the nap length. “Therefore, the adjustments may not be effective,” said Cappuccio.
Akerstedt and his colleagues grouped the 38,000 Swedes according to self-reported sleep duration. Short sleepers slept less than five hours a night. Average sleepers slept the typical seven hours. According to the new study, late risers slumbered for nine or more hours. (The American Academy of Sleep Medicine and Sleep Research Society’s “consensus recommendation” is more than seven hours a night for adults ages 18 to 60.)
The researchers further divided the groups by pairing their weekday and weekend habits. A short-short sleeper got less than five hours a night all week. They had an increased death rate. A late riser slept nine or more hours each night. They too had increased death rates.
The short to medium sleepers, on the other hand, slept less than five hours during the week, but seven or eight hours on their days off. Their death rate was no different from the average.
The differences between weekend and weekday sleep were most pronounced at a young age. People in their late teens and twenties slept an average of seven hours a night during the week, but slept 8.5 hours on days off. Those older than 65 years of age, the standard retirement age in Sweden, reported no difference in how long they slept on the weekend on average – they slept almost seven hours every night on all seven days. That finding was in line with previous reports, Grandner said, which suggested that we sleep less as we age, but our “satisfaction with sleep increases”.
It is not fully understood why both short sleepers and long and late sleepers had above-average mortality rates. Akerstedt emphasized that this study is not an experiment, and these data cannot show that short or long sleep is responsible for higher mortality. Akerstedt suspects that oversleeping is probably no harm, but a sign that something else is wrong.
The scientific jury is not yet sure why too much sleep is linked to an increase in death rates. “There’s no obvious biological mechanism,” said Lauderdale.
This study relied on people describing their own sleeping habits, which Lauderdale believed can create a “mish-mosh” of “accurate and less precise information.”
The voluntary disclosure is a “restriction, but not a fatal error,” said Grandner. Otherwise it is impractical to collect data on this scale. The authors are aware that they do not have a fine brush and accordingly drew a rough overview of their sleeping habits. “It’s a blurry picture, that’s true,” he said.
Grandner urged those who were overworked and who were sleeping under sleep not to regard sleep as wasted time. “We live in a society that considers sleep to be unproductive. What is more un-American than unproductive time?” This is not a healthy approach – since our bodies are built to consume food and water, he pointed out, we are also made to sleep.