The research team at the University of Bristol found that temporal lobe regions of the brain critical to memory became smaller after five years of regular jet lag exposure.

...The findings were said to have broad implications not just for airline staff, but also for shift workers and parents of young children whose body clocks are disturbed during the night.

It was not known how long the brain changes persisted, or whether they were reversible.

Evidence of impaired thinking ability in cabin crews subjected to repeated jet lag had already emerged in a previous study by the same research team from the University of Bristol.
http://news.airwise.com/stories/2001/05/990437565.html