When we get cold, run for the bus or even fall in love, our bodies secrete cortisol, a chemical messenger that is also part of the body's daily routine. Chronic jet lag jams open the body's cortisol tap, Cho's team finds. The body cannot tell whether it is night or day and produces the hormone just in case. Cabin crew who cross more than eight time zones have one-third more cortisol in their saliva than ground staff. Flight attendants serving on shorter flights have lower levels.
Research indicates that cortisol can influence the structure of nerve cells.
Long-term exposure to high levels may affect some brain functions, including memory. Tests show that air hostesses with more than four years service have slower reactions and poorer memories than average. Cabin crews and ground staff were shown sequences of pictures, either 5 or 25 seconds apart, and asked whether the images matched. Cabin crew who work on domestic flights for two weeks, between long-haul treks across the world, are not affected. But the air hostesses surveyed by Cho's team are not so lucky.