Today, Gen. David H. Petraeus, commander of American forces in the Middle East, appeared to faint while testifying before the Senate Armed Services Committee.

"It appears he was maybe a little jet-lagged, dehydrated certainly," Petraeus' spokesman, Col. Erik Gunhus, told the press.

While jet lag really can wreak havoc on the body, passing out may be extreme.

"Fainting or losing consciousness seems like an extreme consequence," said Horacio de la Iglesia, who researches biological clocks and animal behavior at the University of Washington. What is more commonly reported is not being able to stay awake regardless of the stimuli in your environment, he said.

The routine effects of jet lag occur both immediately after a person travels and, for those who experience jet lag frequently, in the long-term. This is due to the body's inability to resynchronize its many biological clocks, researchers say, and can affect every organ in the body, putting a person at heightened risk for a number of ailments.

The body’s  many clocks

It was once thought that the body had a single biological clock in the brain – called the suprachiasmatic nucleus (SCN) – that controls our daily rhythms. But now, researchers know that such “clocks” are found throughout the body, said Alec Davidson, professor of neuroscience at the Morehouse School of Medicine.

The SCN in the brain sends signals to other clocks throughout the body and makes sure that all of the clocks are synchronized. The daily cycles of light and darkness, which are sensed by cells in the retinas of the eyes, help the SCN to set the clock for the rest of the body.

Problems arise when the daily cycle of light and darkness suddenly changes and the SCN must adjust and reset the rest of the clocks because some adjust more quickly than others.

"The SCN is like the conductor of an orchestra," Davidson told Life's Little Mysteries. "In jet lag, it's as if the individual instruments are playing on their own, without a conductor. They can all still play, but it doesn't sound so good."

Body functions thrown off

This lack of synchrony throws off many body functions. For example, digesting a meal and absorbing its nutrients into the bloodstream in a balanced way requires the intestines and the liver to work together. If the liver's clock is not in synchrony with the clock of the digestive tract, the body's nutrient levels may be thrown off.

Over the long-term, the effects can be devastating to the body. Compared with the general population, higher rates of breast, prostate and colorectal cancer, along with increased heart attacks, strokes and ulcers have all been documented in studies of people who work night shifts or who have other odd work hours, Davidson said.

However, Davidson cautions, people in this group also tend to make less money and to have greater amounts of stress, so scientists do not think that working the night shift is the only cause of these heightened risks.

For those traveling through several time zones, though, other factors besides the clock adjustment can contribute to feeling ill. Loss of sleep, dehydration and stress can all play a role.

What controls the clocks

Scientists don't fully understand how the SCN sets the rest of the body's clocks, Davidson said, but it is believed that both nervous system signals and hormonal signals are involved in the coordination.

All the body's clocks are similar in that the same 10 to 15 genes control them, de la Iglesia said. The genes interact, and the result of their interaction is what produces a roughly 24-hour rhythm in every cell.

However, the clock in each organ or tissue may respond to different stimuli, which contributes to the lack of synchrony, de la Iglesia said. For example, the clock within the liver tends to be affected more by your meal schedule than the clock in the brain. Travelers who eat at odd times may make it even more difficult for the clocks to come back into synchrony, he said.

Even among the different stages of sleep, the adjustment period is different, he said. The body's cycle of REM sleep, during which dreaming occurs, takes longer to adjust than non-REM sleep, de la Iglesia told Life's Little Mysteries. The ability to fall into non-REM sleep simply depends on how long a person has been awake, but the ability to fall into REM sleep is more closely aligned with your brain’s biological clock. So a jet-lagged person who has been awake for a long time might fall asleep easily and even think that they are getting enough sleep, but they still might not get the type of sleep they need.

There is strong scientific evidence that it takes about one day to adjust to each hour of a time change, he said, although it takes less time to adjust to adjust to a delay in the clock, as occurs when you travel west, as an advance in the clock, as occurs when you travel east, de la Iglesia said.

A good marker of the biological clock's setting is when the core body temperature reaches its minimum, which usually happens about at 3 a.m.

"If your biological clock thinks that it's 3 a.m. when it's 10 a.m., you feel very sleepy and will have a hard time making sense, no matter where you are and what you're doing," de la Iglesia said.


This article was provided by Life's Little Mysteries, a sister site to LiveScience.