Several past studies have found health impacts of working irregular shifts, such as an increased risk for heart disease. And a new study may have found some negative long-term mental effects of shift work.
Memory, overall brain function and information processing declined when people worked a combination of hours during the night and day, the new study found. But once a person no longer worked shifts, their brain regained its usual cognitive power -- although this took some time.
The researchers called for new strategies to help reduce the mental health problems that people may face from shift work. People who work shifts may wish to switch to working only days when possible, they added.
Jean-Claude Marquié, Ph.D., a research director at the University of Toulouse in France, led the study.
The researchers started out with 3,119 people. All were given surveys and took three mental ability tests. All were tested when they were 32, 42, 52 or 62 years of age, again five years later and five years after that.
At five years after starting the study, 2,183 people from the original group filled out surveys and took the mental ability tests again. At 10 years after the start of the study, 1,253 people from the original group completed this process again.
Of the people who started in the study, 1,484 worked shifts or had in the past, and 1,635 had not.
The authors defined shift work as spending at least 50 days a year working rotating shifts that forced participants to go to bed after midnight, get out of bed for work before 5 a.m. or work through the night.
Marquié and colleagues compared the participants' results on the mental abilities tests. They found that shift work was tied to impaired thinking. For instance, those who had worked irregular shifts for more than 10 years had survey scores comparable to other participants who were about 6.5 years older than them and had not done shift work.
But those who left shift work at least five years before taking the surveys regained their memory and tended to have brain function on par with people their own age. They also improved in how fast they processed their thoughts.
The authors suggested that the cognitive problems tied to shift work may be due to the circadian rhythm — the body’s internal 24-hour clock -- being out of sync from not sleeping on a regular schedule. They also said metabolic syndrome -- a cluster of conditions that occur together, such as high blood pressure and high blood sugar, and put a person at risk for heart conditions -- could play a role. Lack of vitamin D may also be to blame, the authors noted. Most people get vitamin D from the sun, and people who work nights may not have enough sun exposure.
The study authors said those who work shifts for more than 10 years should be monitored for health problems.
In an interview with dailyRx News, Marquié said people can minimize negative effects of shift work on their health in a variety of ways. As much as possible, he said, people should work shifts in a consecutive manner -- such as working days for a time, then nights and then back to days -- rather than moving rapidly through shifts that start at different times. He said those who work irregular shifts should regularly see a doctor.
Marquié also said that those who do this kind of work should learn the benefits of eating well, exercising and remaining social -- activities “which are strongly challenged by shift work.”
This study was published online Nov. 3 in the Journal of Occupational and Behavioral Medicine.
A variety of sources funded this study, such as the French Agence Nationale de la Recherche and the Institute of Occupational Safety & Health. The authors disclosed no conflicts of interest.