The hormone vasopressin may play a key role in jet lag, new research suggests.
The discovery, described today (Oct. 3) in the journal Science, could help scientists one day develop a medicine to help travelers avoid the groggy feeling.
Anyone who has flown across several time zones knows the frustration of waking up in the middle of the night or dozing off midday because the body's circadian clock can take days to adjust to the new time. Typically, it takes people one day to adjust for every hour in time-zone difference they have traveled, so a person traveling from Japan to California, for instance, would take eight days to completely adjust, said study co-author Hitoshi Okamura, a circadian clock researcher at Kyoto University in Japan.
There are a few ways to trick the body's internal clock and partially avoid jet lag. Going hungry prior to the time shift seems to help, because animals are less likely to sleep through a normal mealtime if they are hungry. And the team of researchers who drive the NASA Mars Rover, who wake up and go to bed according to the Martian day, relies on judiciously timed naps and light boxes to keep them in tune with the Red Planet's 24.65-hour days. [7 Strange Facts About Insomnia]
Still, for most people dealing with jet lag, there are no easy solutions.
Okamura and his colleagues noticed that the brain region that drives the master internal clock, the suprachiasmatic nucleus (SCN), was full of receptors for vasopressin. The hormone's known roles include maintaining the body's salt balance by directing the kidneys to retain water, and helping constrict blood vessels. Other studies have tied vasopressin to feelings of love and generosity.
Okamura wondered about the function of all those vasopressin receptors in the brain's clock region.
To find out, the team created genetically engineered "knockout" mice that lacked the brain receptors for the hormone.
They then subjected mice to the next best thing to an intercontinental flight: a completely disrupted day and night schedule.
"It is a seven- to eight-hour time difference, but in these mice, they immediately adapt to the new cycle," Okamura told LiveScience. For people, adjusting to the new time zone would take at least a week.
That suggested that vasopressin's action in the brain was responsible for jet lag.
Next, they gave normal mice an experimental compound that blocked the vasopressin receptors found in the brain, but not other parts of the body.
When those mice experienced a disrupted day-night schedule, they became in sync with the new schedule within three days — not as fast as mice who lacked vasopressin receptors completely, but much shorter than the usual adjustment period.
Jet lag medication?
The findings suggest that a drug that blocks vasopressin receptors only in the brain could lessen jet lag's toll.
However, the compound the researchers used was experimental, and while the mice didn't show any side effects, many more studies will be needed in humans before a jet lag tablet is on the market, Okamura said.
The findings could also be useful for shift workers, he said.
"Shift workers tend to have high incidence of hypertension, metabolic syndrome and breast cancer," so drugs to avoid a disrupted body clock could be helpful for them, he said.