Repeated bouts of jet lag may harm an area of the brain important to memory, according to a recent study in Nature Neuroscience. For the study, researcher Kwangwook Cho of the University of Bristol, England, recruited 20 international flight attendants who routinely worked flights crossing seven or more time zones. Such journeys throw off the brain's internal sleep/wake clock, causing sleep disturbance and general stress and fatigue.

The flight attendants were all women 22 to 28 years old, with five years of service at various airlines. They were split into two groups, based on how long they had to recover between international flights. One group had a full 14 days, while the other group typically only had five days to reset their clocks.     

Cho used magnetic resonance imaging (MRI) to measure the volume of the women's right temporal lobe. Among other things, the temporal lobe is important to memory. The women also took a test for spatial memory-the memory for information such as the geographical layout of your town or workplace.

The short-recovery group, Cho reports, had "significantly" smaller temporal lobe volumes and performed worse on the spatial-memory test. This echoes Cho's previous research, in which flight crews showed impairments in memory and reaction time.

Does repeated, severe jet lag harm the brain? Research by Cho and others points to a role for hormones, such as cortisol, released by the body during times of stress. Frequent jet lag, like growing up in a stressful home, elevates levels of cortisol. There's evidence that long-term exposure to stress hormones can impair memory and other mental skills. It's not known whether the same impairments would be seen in people who suffer occasional jet lag from vacation or business travel.

Further Reading:

"Chronic 'jet lag' produces temporal lobe atrophy and spatial cognitive deficits," by Kwangwook Cho. (Nature Neuroscience, June 2001, vol. 4, no. 6, pp. 567-568.)