Working an irregular shift pattern may be causing long-term damage to people’s memory and mental abilities, new research has shown.
Shift work can disrupt the body’s internal clock in a similar way to jet lag, and has been linked before to an increased risk of health problems such as heart problems and even some cancers.
However, scientists have now found a link between working shifts and a decline in brain function – especially among those whose shifts rotated between morning, afternoon and night.
In a study of 3,000 people living in France, scientists found that those who worked rotating shifts performed significantly worse in memory and cognitive speed tests than people who had worked regular hours.
The level of cognitive decline seen in people who worked irregular shifts for 10 years was equivalent to six and a half years’ worth of natural, age-related cognitive decline, said researchers from the universities of Toulouse and Swansea.
Precisely how shift work might have an impact on brain function is not fully understood.
Disruptions to the body clock – or circadian rhythm – are known to affect the body and the mind. People who regularly fly long-haul have been shown to suffer from poorer brain function, thought to be caused by the breakdown of some brain structures, caused by the over-production of stress hormones.
A similar mechanism may be occurring in people working alternating night and day shifts for a prolonged period of time.
It has also been suggested that night shift workers may be more susceptible to vitamin D deficiencies because of reduced exposure to sunlight. Vitamin D deficiency has been linked to impaired brain function by some studies.
In the French study, 1,200 of the participants were followed up at three different stages, in 1996, 2001 and 2006. One in five of them had worked shift patterns rotating between mornings, afternoons and nights.
Those who were currently or had previously worked shifts had lower scores on memory and processing speed tests than those who worked ordinary office hours.
Researchers found that stopping shift work was linked with an improvement in cognitive function – suggesting that any ill effects are reversible – but said that it took five years out of shift work for this effect to be seen.
Writing in the journal Occupational and Environmental Medicine, the authors, led by Dr Jean-Claude Marquié of the University of Toulouse, said that shift workers’ health should be closely monitored as a result of their findings.
“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,” they write.
“It may also affect shift workers’ quality of life, with respect to daily life activities that are highly dependent on the availability of cognitive resources.
“The current findings highlight the importance of maintaining a medical surveillance of shift workers, especially of those who have remained in shift work for 10 years or more.”