At 3:45 a.m. on a Wednesday morning, there are still a handful of students in Novack Caf, hunched over laptops and textbooks, alternately typing, flipping through notes and frantically swigging coffee. Luckily for them, a new sleep study indicates that getting less sleep may actually be beneficial to your health.
People who sleep between six and seven hours a night have a significantly lower mortality risk than those who sleep more than eight hours or less than four hours, according to the study authored by Dr. Daniel Kripke of the University of California-San Diego.
While sleep experts at the Dartmouth-Hitchcock Medical Center found the findings intriguing, they expressed the opinion that there are a number of problems with the study's methodology.
"What Dr. Kripke and his colleagues have demonstrated is that there is a corralation between sleep duration and mortality risk," said Dr. Glen Greenough of the DHMC Sleep Disorders Laboratory. "But t his kind of association does not necessarily imply causality."
Researchers from the University of California used data collected between 1982 and 1986 by the American Cancer Society as part of a project entitled "Cancer Prevention Study II."
Dr. Peter Nowell of DHMC questioned the study's use of this data set.
"Anytime you use data not originally collected for the purpose of your study, it can be problematic," Nowell said.
Kripke said that researchers used the CPS II data because of the uniquely large sample size of 1.1 million participants and the effectiveness of follow-up.
DHMC psychiatrist Dr. Michael Sateia questioned whether participants represented a truly random sampling of the population, since they were relatives of American Cancer Society volunteers.
The original study controlled for variables such as age, diet and exercise, as well as pre-existing health problems and whether or not participants smoked. Participants' ages ranged from 30 to 102. The median age for women was 57; for men, 58.
All information was based on participants' reports, which meant that undiagnosed health problems such as depression or anxiety disorders, both of which can affect sleep patterns, probably were not factored in when calculating mortality risk, Sateia said.
Apart from the issue of mortality, DHMC doctors cited the detrimental effects that too little sleep can have on quality of life and on basic functions.
A substantial body of literature suggests sleep deprivation is associated with a variety of disfunctions and problems, Sateia said. These include negative effects on mood, performance, attention span, memory, retention and the ability to perform on tests, drive and operate machinery.
The study also showed an increased mortality risk for people using sleep-aid medication.
However, the data was collected during the 1980s, before today's most commonly prescribed sleeping pills were on the market. For this reason, Sateia said, "the public health impact could be entirely different."
He added that sleeping pills are commonly prescribed for several other medical problems, including anxiety and excessive muscular tension, which may themselves contribute to an increased mortality risk.
Kripke vehemently responded to some of the common criticisms of his study.
"Most or all of the critics of this study are people who take money from sleeping pill manufacturers," he said. "There is no doubt that there is an organized publicity campaign to worry people if they don't sleep eight hours and that that campaign is largely supported by sleeping pill manufacturers."
Kripke agreed, however, that "people should not set their alarms earlier on the basis of this study."
Dr. Mark Reed, director of Counseling and Human Development for Dartmouth Health Services, said, "There isn't normal sleep at Dartmouth. Students stay up until all hours of the night -- they get their sleep schedules completely backwards."
Student responses supported his observation.
"I doubt this will cause me to change my sleep habits," Amanda Herring '02 said. "If I could, I'd get eight hours a night, and I don't think I'd really consider if that might be associated with increased mortality."
"I don't think these findings are going to affect anyone's opinion about how much they should sleep -- especially not college students because our sleep schedules are inherently so weird anyway," Noa Gafni '05 said.
DHMC doctors praised the overall intentions behind Kripke's study. "This study is opening up a very good debate," Nowell said. "Hopefully it will lead other investigators to specifically design studies that investigate these issues."
"I think it's worth pursuing this issue further." Greenough said. "It's an interesting association, but a lot more work needs to be done to establish a causal relationship."
