Circadian Rhythm

An experimental drug that mimics the effects of the hormone melatonin can reset the body's circadian rhythms, bringing relief to jet-lagged travelers and night-shift workers, researchers reported Monday. In a study of 450 people who were subjected to simulated jet lag in a sleep laboratory, a team from Brigham and Women's Hospital in Boston found that the drug restored near normal sleep the first night it was used.

Get up at 5 a.m., throw on some sneakers, run out the door, exercise like crazy. Sure, a pre-dawn workout comes with some bragging rights -- just don't expect your best performance. A new study suggests that late night, not early morning, is the best time to exercise, as dictated by circadian rhythms. These rhythms affect the daily production of hormones, brain activity, body temperature -- and workouts.

Much of our knowledge about the body's circadian clock comes from people who volunteer to live for a while in "time-isolation." In Europe, such studies first took place in bunkers and caves in the 1960s. In the U.S., the first time-isolated lab was built on the fifth floor of an old hospital wing in the Bronx in the 1970s. In the 18th century, famed English surgeon John Hunter documented that body temperature drops each night during sleep.

Daylight saving time begins three weeks earlier this year and lasts one week longer -- welcome news for people who relish the extra afternoon light to garden, ride a bicycle, walk the dog or just take out the trash when they can still see the curb. But the extension, which begins Sunday, could actually make millions of Americans feel less sunny.

Too much sunlight in places such as Greenland where long summer days often cause insomnia appears more likely to drive a person to suicide than previously thought. Despite a belief that suicides tend to rise in late autumn and early winter months because of darkness, the new findings suggest that constant sunlight in summer seasons may be just as dangerous. "It is crucial to keep some circadian rhythm to get enough sleep and sustain mental health," Swedish researchers reported Friday in the journal BMC Psychiatry.

Melatonin is secreted by the pineal gland, a tiny hormone-producing organ in the brain. Researchers say that, in animals, the hormone helps determine hibernation patterns. In humans, it is responsible for the circadian rhythm -- the biological cycle that dictates when we sleep and wake. It also plays a role in sexual development. * Uses: The hormone is used primarily to fight insomnia and jet lag and, particularly among older adults, improve sleep quality.

As the old song goes, "Changes in latitudes, changes in attitudes," and for anyone who has been wide awake at 3 in the morning after a cross-country jaunt, this attitude might best be described as seriously out of sorts. "The feeling is like lead in my veins," says Elfi Stoddard, who has been a flight attendant since 1975 and for the last 18 years has been based in Honolulu for Hawaiian Airlines. "I am very tired but can't go to sleep, and very irritable so I snap at my family."

Two genes that regulate the circadian clock -- the 24-hour cycle of life events -- in flies also control how long the insects mate, Oregon State University researchers reported in the journal Current Biology. Researchers found that male flies without one of the two genes, called period and timeless, copulated 30% to 50% longer than flies with both genes, increasing the act from 15 minutes to as long as 23 minutes.

This is how 17-year-old Natalie Kepes starts every school day: 6:30 a.m., buzzzzzzz goes the alarm clock--and slam goes her hand on the snooze button. Buzzzzz, slam. Buzzzzz, slam. Then . . . 7 a.m.? Yikes! No more snoozing. She gets dressed, grabs something to eat and makes a mad dash to El Camino Real High School in Woodland Hills. But she's still not really awake when class starts at, ugh, 8 a.m. Maybe her first-period teacher will let her doze a few minutes. Maybe . . . not.

Humans are much more sensitive to light than previously thought and show bodily responses even to dim indoor lamps, according to Harvard scientists. Two reports in Nature indicate that it could be easier to treat jet lag and other disorders of the 24-hour circadian rhythm than doctors have believed. In one study, researchers exposed young male volunteers to varying levels of indoor light and measured their body temperatures to see how they responded.