People who study sleep and circadian rhythms have long suggested that there is real importance in maintaining a regular schedule that roughly follows the same schedule as the dawning and setting of the sun. Now a new study published in the journal Occupational & Environmental Medicine has strengthened that argument as it reveals that an irregular schedule can have an impact on cognitive abilities.
According to the study, working a schedule that includes working late afternoon and into the night can have long-term impacts on the worker’s brain power, and those who subject themselves to a rotating shift schedule for periods of over ten years suffer a decline that is roughly the same as six and a half years of cognitive losses.
Unfortunately, it doesn’t take as long as ten years for the impact to occur. In fact, those who work just fifty days or more of irregular shifts within a one-year period of time are shown to lose a significant amount of mental ability. For the study, irregular shifts are defined as assigned hours that kept the worker from going to bed prior to midnight or that required them to awaken earlier than five o’clock in the morning. With just that roughly fifteen percent of interruption, workers displayed cognitive losses equal to 4.3 years of age-related decline.
This decline was prevent even if the shift work had occurred far in the past, indicating that once these particular types of losses occur there is no recovery of ability, though some recovery was shown in cases where the shift work schedules had been at least five years previous, with no intervening shift work during that time. But for those whose shift schedules were ongoing during the course of the study, scores were found to be low, with a decline of 5.8 year equivalence to age related decline. Lowest of all were those who had been working shift work during the previous five years but who no longer were. Their scores showed a 6.9 year age-related cognitive decline.
The researchers utilized information that had been conducted in a long-term study called VISAT. Data was gathered by conducting three surveys a year over a ten-year period from over 3,200 salaried workers southern France. The workers also submitted to clinical exams. Out of the entire group, almost 1,500 had worked irregular shifts at some point in their careers.
This is not the first study to indicate that work schedules that put the body out of sync with natural rhythms has a deleterious effect. Previous research has shown that airline crews who frequently suffer from jet lag and who have insufficient recovery time test poorly on cognitive tests, and industrial workers assigned to shift work do poorly on memory tests. The same has held true for nurses who have worked night shifts. The researchers concluded that these modifications to the body’s normal schedule cause “physiological stress, which has been shown to have an impact on brain structures involved in cognition and mental health.”