"This particular study of about 100 subjects, which Dr. Goel is leading, aims to see if people respond equally to two different types of sleep deprivation. It compares acute, total sleep loss (going 36 hours without sleep) with chronic sleep deprivation (in this case, just four hours of sleep between 4 a.m. and 8 a.m. for five nights). Preliminary results indicate that the answer is yes, Dr. Goel says.
“There are huge individual differences. [But] if you are resilient to total sleep loss, you are resilient to being chronically sleep-deprived or if you’re vulnerable to one, you are vulnerable to the other,” she says.
The study is also looking for genes and other so-called biomarkers—substances in the blood—that can predict which people are more vulnerable to the effects of sleep loss. Dr. Goel says the researchers expect to finish the study later this year.
In earlier studies, the Penn lab and others have found that attention, reaction time and cognitive speed tend to be particularly affected by sleep loss. This is a big problem for driving. Higher cognitive functions, like reasoning, tend to be less affected. Mood plummets: People interpret even neutral facial expressions as more negative. Sleep-deprived subjects also eat more and gain weight: In Penn studies, they eat about 500 extra calories a day, veer toward fat-laden foods and gain about 2 pounds in a week.
But not everyone tolerates sleep loss the same: In general about one-third of people are resistant to the effects of sleep loss, one-third are vulnerable and one-third are somewhere in the middle, Dr. Dinges says.
The study is being funded by the Office of Naval Research. Dr. Dinges has also just completed a study looking at how long it takes to recover from sleep deprivation. In earlier studies, it seemed to only take a few days of regular shut-eye for people to recover from sleep loss and perform like they were well-rested.
But this new study seems to refute that. People might seem fine, but if they lose sleep again, their performance plummets more than expected. “There’s a memory in this biology,” Dr. Dinges says. “They are carrying a vulnerability.”
If the results hold up and are replicated, he says, the days of human sleep-deprivation studies might be numbered. “If I can’t reverse what I’ve induced, then these experiments are no longer ethical,” he says. “I’ve got to stop doing this.”"