The Winged Chariot of Time

The Jet set’s mixed-up clock

The human clock cannot, however, reset itself to today’s jet speeds. In the six-and-a-half-hour flight from New York to London, a traveler will get himself five hours out of step with the daily rhythm of activities and will probably feel tense, tired and irritable. Studies carried out by the Federal Aviation Agency show that these tense feelings are not imaginary; a rapid shift across time zones produces consistent and measurable disruption of physiological processes. A group of volunteers was flown from Oklahoma City to Manila (a time difference of 10 hours) and then tested. During the first 24 hours after arrival none of them could concentrate long enough to add a column of 10 two-digit numbers. For some, their “reaction” time (which is of crucial importance in driving a car safely) more than tripled. Similar experiments with a north-south flight of equal length, in which the time difference was an hour or less, produced no functional impairments.

The “time-zone syndrome” is even more important in the case of airline pilots, who seldom have the time to adjust completely before winging back to their original time zone- and whose job requires the utmost in mental alertness. Many of them definitely prefer north-south to east-west flights; says one: "Flying from New York to Buenos Aires, my digestion can still work on Eastern Standard Time!"

It takes at least 24 hours for mental alertness to return to normal after a long flight across time zones. Indeed, the body’s temperature cycle does not adjust to the “new” time for several days longer. As a result, FAA psychologists have recommended that tourists flying east or west should rest for a day before embarking or strenuous sightseeing programs, and that executives or diplomats should not undertake any important business in the first 24 hours after arrival.

Scientists studying human circadian rhythms are experimenting with drugs that can be used to reset biological clocks, with the hope that they may one day be able to prescribe exact drug dosages to help ease the special problems of jet travelers and workers changing shifts.

Unlike plants or other animals, man appears to lack built-in seasonal rhythms. Perhaps, having evolved I the tropics, “where winter never comes,” he never developed them. He does not migrate with the birds or hibernate with the rodents. His metabolism, to be sure, changes somewhat with the seasons, but it does not appear to anticipate them. A warm, moist April day, impinging on our still-“winterized” bodies, brings on the delicious languors of spring fever year after year.

Nor, for that matter, does man mate or spawn at any special time of the year. In these as in his other activities, he remains a man for all seasons.

Resetting the Biological Clock is a problem for most travelers, who may fail to adapt to local time for several days after a long trip (as shown on the left). On a flight from Tokyo to Seattle, the traveler who leaves Japan at 6 p.m. Tuesday may already have eaten dinner (top right). His biological clock is perfectly synchronized with local time (top left). He then flies East for 8 and a half hours, crossing six time zones, and arrives in Seattle at 9:30 Tuesday morning local time (lower left). But his biological clock (lower right) is still tuned to Tokyo time and he feels as if it were 2:30 a.m. Wednesday. Instead of being wide awake and ready to face the day, he is badly in need of a good eight-hour sleep.