Findings of a new study could yet again scare shift workers. A team of international researchers has found that long-term shift work is not only associated with a range of health problems including ulcer, cancer and cardiovascular disease. It is also linked with impaired brain power which could affect a person's memory and thinking.

For their new study, which was published in the journal Occupational & Environmental Medicine on Nov. 3, Jean-Claude Marquie, from the National Center for Scientific Research at the University of Toulouse in France, and colleagues tracked the cognitive abilities of 3,232 individuals, 1,484 of whom experienced shift work while 1,635 of the participants had not.

The researchers found that the participants who were either working or had previously worked in shift or odd hours had lower scores on memory, thinking and processing speed compared with the participants who had never experienced working in shifts.

They also found that the participants who worked in rotating shift patterns for at least 10 years had lower memory and cognitive scores compared with the participants who had never experienced working rotating shifts. The difference is equivalent to more than 6 years of age-related memory and thinking skills decline.

"Shift work was associated with impaired cognition," the researchers wrote. "The association was stronger for exposure durations exceeding 10 years (dose effect; cognitive loss equivalent to 6.5 years of age-related decline in the current cohort)."

Sleep expert Christopher Colwell, from the University of California, Los Angeles, said that in animal studies, one of the things that happen during sleep is the brain storing information into long term memory. Thus, when sleep is disrupted the storage information could be affected as well.

Marquie and colleagues also wanted to find out if stopping shift work was associated with recovery in cognitive abilities and found that while it was possible, reversal would take no less than five years after a person stops shift work.

It should be noted that the study does not prove a cause and effect relationship which means that it did not prove that sleep is indeed the definitive cause of diminished brain power. Nonetheless, the researchers said that the impaired brain power they have observed in their study could have wide-scale implications.

"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," the researchers said.