November 3, 2014
Science Daily/BMJ-British Medical Journal
Long term shift work is linked to impaired brain power, finds research. The impact (for rotating shift patterns, at least) was stronger after a period of 10 or more years of exposure. And although the effects can be reversed, recovery may take at least five years, the findings suggest.

The second set of analyses looked at the impact of working a rotating shift pattern and found that compared with those who had never worked this type of shift, those who had, and had done so for 10 or more years, had lower global cognitive and memory scores -- equivalent to 6.5 years of age related cognitive decline.Finally, the researchers looked at whether stopping shift work was linked to a recovery in cognitive abilities.

The results indicated that it was possible to regain cognitive abilities after stopping shift work, but that this took at least five years, processing speeds excepted.

This is an observational study so no definitive conclusions can be drawn about cause and effect, but the disruption of the body clock as a result of shiftwork could generate physiological stressors, which may in turn affect the functioning of the brain, suggest the researchers.
Other research has also linked vitamin D deficiency caused by reduced exposure to daylight, to poorer cognition, they point out."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.

At the very least the findings suggest that monitoring the health of people who have worked shift patterns for 10 years would be worth while, they say.
http://www.sciencedaily.com/releases/2014/11/141103192034.htm