In what would come as bad news for shift workers, not only does working irregular hours hit one's social life and likely one's health, more worryingly it had an adverse impact on one's ability to think, according to a new study, CNN reported.
The study, published in the journal Occupational and Environmental Medicine, focused on the long-term impact on people's cognitive abilities of working at odd hours or with frequently changing shifts.
The subjects of the study, employed and retired workers in France and the UK, were followed by the researchers over the course of a decade. Some of the workers had never worked shifts, while others had worked them for years.
The researchers found that shift work was associated with a decline in cognition, with the impairment worse in those who had done it for longer.
Those who had worked abnormal hours for over 10 years showed a response that was particularly marked, with a loss in intellectual abilities equivalent to the brain having aged 6-1/2 years.
The only bright spot for shift workers was that the decline could be reversed by a switch to regular hours, but it took at least five years, according to the research, except for processing speeds.
According to experts, the findings could be important in dementia, as many patients had disrupted sleep, BBC reported.
The design of the body's internal clock was based on activity during the day and rest at night.
Though the brain naturally declined with age, according to the researchers, working antisocial shifts accelerated the process, BBC reported.
Dr Philip Tucker, part of the research team in Swansea, told the BBC that it was quite a substantial decline in brain function. He added it was likely that when people tried to undertake complex cognitive tasks then they might make more mistakes and slip-ups, maybe one in 100 made a mistake with a very large consequence, but it was hard to say how big a difference it would make in day-to-day life.
He added he would not do night shifts "if I could possibly help it" but they were a "necessary evil" that society could not do without.
There were ways to mitigate the effects in the way one designed work schedules and regular medical check-ups needed to include cognitive performance tests to look for danger signs.