Sleeping in on a day off feels marvelous, especially for those who don't get enough rest during the workweek. But are the extra weekend winks worth it? It's a question tackled in a new study by psychologist Torbjorn Akerstedt, director of the Stress Research Institute at Stockholm University, and his colleagues.
Akerstedt's team tracked more than 38,000 people in Sweden over 13 years, with a focus on their weekend vs. weekday sleeping habits. This peek at weekend slumber fills an "overlooked" gap in sleep science, Akerstedt said.
Previous studies asked people to count their hours of sleep for an average night, without distinguishing between workdays and days off. People under age 65 who slept five hours or less every night, all week, did not live as long as those who consistently slept seven hours a night.
But weekend snoozers lived as long as the well-slept, the study found. People who slept fewer than the recommended seven hours each weekday, but caught an extra hour or two on weekends, lived as long as people who always slept seven hours, the authors reported.
"It seems that weekend compensation is good" for the sleep-needy, Akerstedt said, though he cautioned that this was a "tentative conclusion" of the research.
Epidemiologists told The Washington Post that the result is a plausible finding, if not a statistically robust one, that deserves more investigation.
Sleep is not like a financial transaction, said Michael Grandner, director of the Sleep and Health Research Program at the University of Arizona's College of Medicine.
We can't deposit zzzs over the weekend and expect to cash them later, Grandner said.
A better metaphor is a diet, he said. For the sleep-deprived, sleeping in on a weekend is like eating a salad after a series of hamburger dinners - healthier, sure, but from "one perspective, the damage is done."
In September 1997, thousands and thousands of Swedes filled out 36-page health questionnaires as part of a fundraiser for the Swedish Cancer Society.
The study's authors followed 38,015 survey participants over 13 years to track their mortality rates. Between 1997 and 2010, 3,234 of these subjects died, most as a result of cancer or heart disease. That's about six deaths per 1,000 people per year. By comparison, the world mortality rate in 2010 was nearly eight in 1,000.
The researchers tried to account for the usual gremlins that influence sleep: alcohol consumption, coffee intake, naps, smoking, shift work and similar factors, and they used statistical methods to control for their effect.
"The only thing that we don't have control over is latent disease," Akerstedt said, meaning diseases that went undetected in a person's life.
But even by 1997 Swedish standards, this group was not representative of most people, said Diane Lauderdale, an epidemiology professor at the University of Chicago.
Fewer than average were smokers, for instance. (People who regularly smoke might not be as eager to participate in a cancer society event, she said.)
Epidemiologist and cardiovascular doctor Franco Cappuccio at the University of Warwick in England also not a member of the research team, said the study "looks good," but the authors missed a trick: "a full explanation of the possibility of daytime napping."
The researchers only asked if people took daily naps but did not quantify nap length. "Therefore the adjustments may not be effective," Cappuccio said.