Long term shift work is linked to impaired brain power, research published in Occupational & Environmental Medicine has found.
The impact was stronger after 10 years for rotating shift patterns and recovery may take at least five years, the findings suggest.
Those who currently or previously had worked shifts had lower memory, processing speed and overall brain power than those who worked only normal office hours.
Analysis of those who worked rotating shift patterns for 10 or more years found lower cognitive and memory scores, equivalent to 6.5 years of age related decline.
Recovery of cognitive abilities was found to take at least five years, processing speeds excepted.
Shift work is known to disrupt the body's internal clock (circadian rhythms) and is linked to health problems including ulcers, cardiovascular disease, metabolic syndrome and some cancers.
Little had been known about its impact on brain function such as memory and processing speed.
The researchers tracked the cognitive abilities of more than 3000 people who were working in a range of sectors at five year intervals from 1996 to 2006.
Just under half the sample had worked shifts for at least 50 days a year, participants were tested for long and short term memory, processing speed and overall cognitive abilities. 1197 participants were tested at all three stages.
The researchers, who include Dr Philip Tucker, a researcher at the Stress Research Institute in Stokholm, who is based at the Department of Psychology at Swansea University, said: "The cognitive impairment observed in the present study may have important safety consequences not only for the individuals concerned, but also for society as a whole, given the increasing number of jobs in high hazard situations that are performed at night."
