One of the more ludicrous examples of a study being used as part of a scare campaign were reports last week of a new study that found sleeping 8 to 10 hours each night increases the risk of dying. Unfortunately, not only was this study poorly designed but its results weren’t all that impressive.
Researcher Daniel Kripke used surveys filled out by 1.1 million men and women from 1982-1988. Among the survey questions were several pertaining to the amount of sleep the individuals received as well as whether or not they took sleeping pills.
Kripke’s study, published in the Archives of General Psychiatry, found that those who slept 8 hours increased their risk of dying by 15 percent, those who slept 9 hours increased the risk by 20 percent, and those slept 10 hours a night had an increased risk of 35 to 40 percent.
Even if all of the data is absolutely correct, a 15 to 40 percent increased risk in this sort of epidemiological trial is hardly anything to get worked up about. This is a level of risk that is difficult to distinguish from background noise in this sort of study.
Moreover the validity of the data here are highly questionable. First, the study relies entirely on people’s self-reporting of how much they sleep. As one critic of the study noted, however, people generally respond to such questions with an estimate of how much time they spend in bed rather than how much they sleep. Even then, it’s questionable whether people can give reliable estimates (how many people reliably track what time they go to bed and wake up — allowing for events such as waking up in the middle of the night, etc.?)
As Dr. Russell Rosenberg, director of the Northside Hospital Sleep Medicine Institute in Atlanta, Georgia, told CNN,
The data can’t be used to establish a cause and effect relationship because there are flaws in the study. You can’t tell how people rated their own sleep quality and looked back at their sleep, which is a subjective reaction to how much sleep they were getting.
Secondly, the study does not appear to have controlled for confounding factors. People who are already ill, for example, would be expected to spend more time in sleeping than people who are not ill. Kripke could simply be measuring the fact that people who are sick tend to sleep more which is hardly groundbreaking news.
Either way, there is plenty of research suggesting that the amount of sleep people receive strongly affects their ability to remain alert. Based on the weak findings of this study, it would be a mistake to alter sleeping patterns to try to achieve a likely non-existent benefit in life expectancy.
Experts challenge study linking sleep, life span. Rhonda Rowland, CNN, February 15, 2002.
Study links 8 hours’ sleep to shorter life span. Shankar Vedantam, Washington Post, February 15, 2002.