Sleep strategy used by night nurses throws off their circadian clocks

As many as 25 percent of hospital nurses go without sleep for up to 24 hours in order to adjust to working on the night shift, which is the least effective strategy for adapting their internal, circadian clocks to a night-time schedule.

That is one of the results of the first study to examine the strategies that night nurses use to adjust between day and night sleep cycles. The study was based on questionnaires from 388 nurses who work at the Vanderbilt University Medical Center and the results are published in the April 13 issue of the scientific journal, Public Library of Science One.

The study also found that variations in individuals’ circadian clock genes have a discernable impact on the nurses’ ability to adapt.

Disruptions to circadian rhythm unhealthy

A number of previous studies have found that repeated incidence of circadian misalignment – the condition that occurs when individuals’ sleep/wake patterns are out of sync with their biological clocks – is not healthy. Jet lag is the most familiar example of this condition. Circadian misalignment has been associated with increased risk of developing cardiovascular, metabolic and gastrointestinal disorders, some types of cancer and several mental disorders.

The way that nursing shifts have been scheduled since the nurse shortages of the 1980’s makes nurses particularly susceptible to this problem. Hospital nurses who work with inpatients do so almost exclusively in 12-hour shifts. The day shift normally runs from 7 a.m. to 7 p.m. and the night shift covers 7 p.m. to 7 a.m.

Vanderbilt night shift nurses typically work a schedule that includes three days on night shift 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,” said Karen Gamble, an 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.”
Five distinct sleep strategies

The researchers identified five distinct strategies that the nurses used to adjust their circadian clocks. The most common approach, used by about half the participants, was to sleep in late on the morning before their first night shift. 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,” said Vanderbilt graduate student and co-author Chris Ciarleglio.