Most people you know probably talk about not getting enough sleep, but the percentage of U.S. adults who sleep for more than nine hours a night is actually on the rise, a new study suggests.
Between 1970 and 2007, the percentage of survey participants who reported sleeping for more than nine hours over a 24-hour period increased from 28 percent in 1985 to 37 percent in 2007, the study found. The trend was seen in participants' reports of both their weekday and weekend sleep habits.
What's more, the percentage of people who slept for less than six hours a night decreased, from about 11 percent in 1985 to 9 percent in 2007, the researchers said.
"This turns the current concept of an increasingly 'sleep-deprived society' on its head," the researchers write in the March 22 issue of the American Journal of Epidemiology.
Although there's been lots of talk about society sleeping too little, not much attention has been paid to the problem of too much sleep. However, studies show that sleeping more than nine hours a night is linked to an increased risk of heart disease, thinking problems and premature death, the researchers said.
A 2010 study published in the journal Sleep also found that there has been no overall increase in the percentage of U.S. adults who sleep for less than six hours, although there was an increase among full-time workers.
The new study, conducted by researchers at the University of Sydney, examined information from surveys done in 10 countries which asked participants to record how much time they allocated to different tasks in a 24-hour period. The study included surveys from over three decades. (Surveys in each country were from a nationally representative sample of that country's population.)
The U.S. participants were about 1.5 times more likely to report sleeping for more than nine hours a night, and 15 percent less likely to report sleeping less than six hours, in 2007 compared to 1985.
The study found a similar trend in other countries — Australia, Finland, Sweden, and the United Kingdom all reported increases in the percentage of people who slept for more than nine hours a day (only Canada and Italy reported decreases). Sweden and the United Kingdom also saw decreases in the percentage of people who slept for more than six hours, while Italy and Norway had increases.
"One does hear again and again…that people are sleeping less than they used to. There's never been any good evidence for that," said Diane S. Lauderdale, a professor of epidemiology at the University of Chicago's Department of Health Studies, who was not involved in the study.
One reason it may seem like we're sleeping less is that, as we grow up, we do, in fact, sleep less than we used to in childhood or as teenagers. "It makes sense to people, because everybody has experienced that" as they mature, Lauderdale said.
However, it's important to note that the way people define "sleep" can be ambiguous, and it's possible that in the study, participants recorded how long they spent in bed, rather than how long they actually spent sleeping, the researchers said. People are probably sleeping for most, but not all, of the hours they indicated on the survey, Lauderdale said.
It's not clear if long sleep duration itself is responsible for poor health outcomes, or if it is a sign of other problems, such as depression or reduced physical activity. It's possible that people in the study who appeared to sleep for a long time actually had trouble sleeping, and so they stayed in bed for longer, Lauderdale said. More research is needed to investigate the link between long sleep duration and poor health, she said.