No sleep upends nurses’ circadian clock

VANDERBILT (US) — In order to adjust to working the night shift, some nurses stay awake for as many as 12 hours before the shift begins—the worst strategy for adapting their internal clocks.

A new study, based on questionnaires from 388 nurses who work at the Vanderbilt University Medical Center, also finds that variations in individuals’ circadian clock genes have a discernable impact on the nurses’ ability to adapt.

The results are reported in the journal PLoS One.

Hospital nurses who work with inpatients do so almost exclusively in 12-hour shifts, typically on a three day work schedule followed by two to five days off, when most switch back to a normal sleep cycle. That means most of them are shifting sleep cycles as frequently as twice a week.

“I was very surprised to find that nurses’ second most frequent strategy was the ‘no sleep’ strategy that often involved staying awake for the 12 hours before starting the night shift,” says Karen Gamble, assistant professor of psychiatry and behavioral neurobiology at the University of Alabama at Birmingham, who worked on the study as a post-doctoral fellow at Vanderbilt. “That means they are skipping sleep for at least 24 hours straight.”

The researchers identified five distinct strategies that the nurses used to adjust their circadian clocks. The most common approach, is  to sleep late on the morning before their first night shift begins. A small percentage maintained a nighttime schedule on their days off. The other two strategies were intermediates.

“It’s not often that you identify and characterize a human behavior for the first time, let alone one that has an effect on human health,” says Vanderbilt graduate student and co-author Chris Ciarleglio.

It was beyond the scope of the study to determine the effect that the nurses’ sleep strategies have on their performance. “It’s very difficult to differentiate between the strategies and the individual variations of the people who choose them,” Gamble says.

The study asked nurses several questions designed to assess their adaptation. For example,  how well adapted they felt; how long it takes them to get out of bed; how much caffeine they use; and how likely they are to fall asleep during the day.

The answers to these questions indicate that the nurses who use the sleep deprivation strategy are the most poorly adapted of the five groups.

Nurses should avoid the “no sleep” strategy when working nights and hospitals should re-evaluate the way that they schedule nurses to reduce the frequency with which nurses switch sleep schedules.

“Most people don’t want to work at night and those that do use what works best for them and their lifestyle,” says co-investigator Nancy Wells, director of nursing research. Scheduling is a touchy issue and many nurses, particularly the younger ones, like the current system because it allows them to string together a number of days off without taking vacation.

DNA samples from the participants was used to study the extent to which their circadian clocks influenced their adaptation. Nurses’ “chronotype” – whether they are natural early risers (larks) or late risers (owls) – and which of seven well-known variations, or polymorphisms, in human circadian clock genes that
each nurse possessed.

Nurses use several different sleep strategies to adapt to a noctural schedule. (Credit: Carlson Laboratory, Vanderbilt U.)

This information allowed the researchers to determine that larks adapt particularly well to day shifts and particularly poorly to night shifts, while owls do not adapt particularly well or poorly to either shift.

In addition, they found that variants in one gene, called PER3, appear to have a major impact on the effectiveness of the no sleep strategy. Individuals with one variant of this genotype appear to respond more poorly than average to the strategy while those with the other genotype appear to respond better than

The research was funded in part by the National Institute of Mental Health.

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