Working the night shift or any irregular shift dulls our minds, said a new study from the University of Toulouse in France.

For people engaged in "shift work" for more than 10 years, the effects are equivalent to 6.5 years of normal age-related decline in memory and thinking skills.

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The study published in Occupational & Environmental Medicine also found out that even people on any type of irregular work schedule like mid-shift for at least 50 days also suffered significant mental damage.

Results showed these people had the equivalent of an average of 4.3 years of age-related cognitive decline over the years.

It also gathered evidence that people's brains could recover from the situation after the working schedule switched to a normal one. This recovery takes some five years.

"Our work suggests that shift work is associated with impaired cognition, that the association is stronger and especially significant for exposure durations exceeding 10 years, and finally, and maybe most importantly, that the effect persists after having ceased any form of shift-work schedule," said Jean-Claude Marquie, research director at the National Center for Scientific Research from the University of Toulouse.

There were 3,000 participants in the study from different regions in France. They were employed in a wide range of sectors or had retired. Men and women aged 32, 42, 52, and 62 took the first set of tests to measure their memory, processing speed and overall thinking ability.

The study took place in 1996, 2001 and 2006. Half of the participants experienced shift work for at least 50 days of the year.

More than 1,000 current and retired employees had rotating work shifts that switched back and forth in the mornings, afternoons and evenings.

Rotating shift workers had lower overall memory and thinking ability scores compared to those who did not.

Even lower scores were obtained from people who had rotating working shift for more than 10 years.

The study is additional evidence that screwing-up the circadian rhythm can lead to "physiological stress, which has been shown to have an impact on brain structures involved in cognition and mental health."

TagsBrain damage, thinking ability, night shift work, rotating work shift