Forget about jet lag, and much more

World-weary travelers take heed: You should schedule a break before hopping on yet another flight to a distant time zone. A new study suggests that chronic jet lag shrinks the brain.

Temporary fatigue, drowsiness, and loss of concentration are typical symptoms of isolated bouts of jet lag (SN: 9/18/99, p. 189). Now, a report in the June Nature Neuroscience hints that more ominous consequences wait in the wings for airline flight crews who repeatedly cross many time zones. Kwangwook Cho of the University of Bristol Medical School in England found that flight attendants with chronic jet lag have higher stress-hormone concentrations in their saliva and smaller temporal lobes than more rested attendants do. The temporal lobes are critical brain areas for processing short-term memory.

Cho’s own difficulties with confusion and forgetfulness after trips across the Atlantic inspired him to study the long-term effects of jet lag on the brain. Also, flight attendants had told him of their frequent troubles, such as losing hotel keys.

Cho took saliva samples and brain scans of healthy women in their twenties who had been employed by international airlines for 5 years. Their schedules had included flights crossing at least seven time zones, interspersed with short or long periods of flying within a single time zone.

Half the women had had fewer than 5 days between multizone flights and half had had at least 2-week sessions of the shorter flights. The first group had higher saliva concentrations of the stress hormone cortisol, smaller temporal lobes, and more difficulty in tests of short-term memory. Many studies have shown that high cortisol concentrations damage brain cells. If this is the case in jet lag, the shrinkage is permanent, says Cho.

His findings may have implications for other people whose irregular work schedules play havoc with their sleep cycles, says Cho. Next, he plans to study nurses and journalists.