Long term shift work could be linked to impaired brain power, scientists have warned.
Researchers from the University of Swansea and the University of Toulouse investigated what impact shift work had on brain functions, such as memory and processing speed.
The study, published in Occupational & Environmental Medicine, suggested that the impact was most noticeable over a period of 10 or more years, and although the effects can be reversed, this may take at least five years.
"The study shows the long term effects of shift work on the body clock are not only harmful to workers' physical health, but also affect their mental abilities," said Dr Philip Tucker, a professor of psychology at the University of Swansea.
"Such cognitive impairments may have consequences for the safety of shift workers and the society that they serve, as well as for shift workers' quality of life."
The researchers tracked the cognitive abilities of more than 3,000 people, who were either working in a wide range of sectors or who had retired, at three time points: 1996; 2001; and 2006.
The study found that just under half (1,484) of the sample, which was drawn from the patient lists of three occupational health doctors in three different regions in southern France, had worked shifts for at least 50 days of the year.
Participants were aged exactly 32, 42, 52 and 62 at the time of the first set of tests, which aimed to assess long and short term memory; processing speed; and overall (global) cognitive abilities.
In all, 1197 people were assessed at all three time points.
Around one in five of those in work (18.5%) and a similar proportion of those who had retired (17.9%) had worked a shift pattern that rotated between mornings, afternoons, and nights.
The data showed that those who currently or who had previously worked shifts had lower scores on memory, processing speed, and overall brain power than those who had never worked shifts.
The second set of analyses looked at the impact of working a rotating shift pattern and found that compared with those who had never worked rotating shifts, those who had, and had done so for 10 or more years, had lower global cognitive and memory scores—equivalent to 6.5 years of age related cognitive decline.
The researchers also looked at whether stopping shift work was linked to a recovery in cognitive abilities.
The results indicated that it was possible to regain cognitive abilities after stopping shift work, but that this took at least five years, processing speeds excepted.