People who work for years on rotating shifts are more likely to lose some of their brain power compared to those who do 9-5, researchers warn today.
But the effects on brain function, such as memory and processing speed, can be reversed over time, according to the observational study, which is published in Occupational & Environmental Medicine.
Researchers from the Université de Toulouse-CNRS, Université de Toulouse-Inserm, Toulouse, France, Swansea University, Wales, Stockholm University, Sweden, Université Paris Descartes, France, and the International University of Monaco, tracked the cognitive abilities of more than 3,000 people who were either working or who had retired in 1996, 2001 and 2006.
All the participants, who were aged 32, 42, 52 and 62 at the time of the first set of tests, were drawn from patient lists of 3 occupational health doctors in 3 different regions in southern France. 1,484 of the cohort had worked shifts for at least 50 days of the year.
The tests assessed long- and short-term memory, processing speed, and overall cognitive abilities. 1197 people were assessed all 3 times.
The researchers found that about 1 in 5 of those in work (18.5%) and 17.9% of those who had retired had worked a shift pattern that rotated between mornings, afternoons, and nights.
The first set of analyses looked at whether any abnormal working hours were associated with a decline in cognitive abilities.
The data showed that those who currently, or who had previously, worked shifts scored lower marks for memory, processing speed, and overall brain power compared with those who worked normal office hours.
The second set of tests examined the impact of working a rotating shift pattern. Those who had worked a shift pattern for more than 10 years had lower global cognitive and memory scores—equivalent to 6.5 years of age-related cognitive decline – compared with those who had never worked a rotating shift.
Results from the third analysis suggested that it is possible to regain cognitive abilities after stopping shift work, but that it would take at least 5 years.
The research team said although no definitive conclusions could be drawn about cause and effect, the disruption of the body clock as a result of shift work could generate physiological stressors, which may in turn affect the functioning of the brain.
Previous research has linked vitamin D deficiency caused by reduced exposure to daylight, to poorer cognition.
“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,” warn the researchers.
They suggest that monitoring the health of people who work rotating shifts could be worthwhile.
Marquié JC, Tucker P et al. Chronic effects of shift work on cognition: findings from the VISAT longitudinal study. Occup Environ Med 2014. 0:1–7; doi:10.1136/oemed-2013-101993
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