Circadian Rhythms

The human circadian rhythm, a tyrant that dominates human existence, may be reset far more easily than previously believed, according to a new study in today's issue of Science magazine. The study comes at a time of increasing research into the mysterious, periodic cycles that govern life, and such studies are yielding new knowledge that is of potential benefit to millions of people who work non-traditional hours.

Surgical residents were more fatigued than expected, especially on night rotations, according to a new study. A quarter of their waking time, they were the equivalent of being legally drunk, the study said. “Our fatigue levels were higher than we thought, but that allows us to focus on where the problems are likely to be,” Frank McCormick, a doctor from the Harvard Combined Orthopedic Residency Program and the lead researcher, said by telephone. The study, published Monday in the journal Archives of Surgery, did not measure actual harm to patients from fatigue, just potential, he said.

Getting a good night's sleep--or a good day's sleep if you prefer--is more easily accomplished when you're in sync with your body's internal clock. * Body temperature, exposure to light and what a person eats all affect how that clock--known as circadian rhythm--runs. While many of us use an alarm clock to awaken, research shows that when our bodies are allowed to run unencumbered by clocks, an internal gauge keeps us up and puts us to bed at certain times.

There's a lot you can read about on Twitter — including, it now appears, the patterns of human moods. After analyzing two years' worth of tweets by 2.4 million people around the world, researchers at Cornell University have concluded that individuals wake up happy but that their mood deteriorates as the day progresses. That discovery, among others reported Thursday in the journal Science, will interest researchers who are trying to understand how circadian rhythms and other natural influences shape our states of mind.

Researchers have obtained their first peek into circadian rhythms, the hitherto mysterious internal clock that tells humans and other animals when to fall asleep and wake up and that regulates a host of other biological functions, such as hormone release and body temperature.

AT 6 a.m., the hospital's bright hallway lights flicker on, signaling the start of a new day. Doctors in crisp business clothes appear on their early-morning rounds, and the clang of breakfast carts will soon echo through the unit. For registered nurse Liberty Bunag, however, it's finally time to go home and sleep. She began her shift 12 hours ago with an extra-large coffee and since has consumed a liter of caffeinated soda, more coffee and lots of rice, her personal energy food. Sometimes she and the other nurses on the orthopedic ward of White Memorial Medical Center in Los Angeles practice foreign languages to stay alert, squelching the yawns and drowsiness -- the body's way of protesting this nocturnal activity.

Doctors often wonder if there is a best time of day for cancer patients to receive chemotherapy. Past research suggests there probably is an optimal time based on the body's circadian rhythms. Now a compelling new study offers some biological proof for the idea. Researchers at the University of North Carolina have discovered that chemotherapy is probably most effective at particular times of day when an enzyme system in the body that can blunt the effect of the drugs is at its lowest levels.

New evidence confirms that mankind's daily cycles of sleeping and waking, so easily disrupted by travel through different time zones, are driven by an internal chemical mechanism rather than by environmental cycles of light and darkness, researchers say. The new information results from a study of a recently discovered strain of hamsters whose daily rhythms, called circadian rhythms, are four hours shorter than normal.

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.

Years ago, it used to be standard practice for hospital nurses to leave bright lights on all the time in neonatal intensive care units because it helped the staff better attend to premature infants' urgent medical needs. Over the years, though, researchers found that constant light was stressful for preemies, so many NICUs switched to near-darkness, aiming to mimic the darkness of the womb.

Melatonin may hold the key, or one key, to treatment of summer seasonal depression. The hormone, produced naturally by the human body, is frequently taken as a supplement to help travelers adjust to new night and day cycles and to help insomniacs get to sleep. Very early research suggests that this ability to affect the body's circadian rhythms could make the hormone a potential treatment for depression triggered by seasonal changes as well. Melatonin is a hormone that sets the seasonal rhythms in animals, such as the timing of breeding seasons and coat growth.

When a magnitude 8.8 earthquake struck South America last weekend, the ground rumbled in Chile, the sea rose in the Pacific, and a day on Earth got shorter. Not by much. Earthlings ended up losing 1.26 millionth of a second of a day. You can't sense it. Nor is your dog aware of it. But while other experts charted the shift of tectonic plates and the swell of ocean waters wrought by the quake, geophysicist Richard Gross mathematically calculated the temblor's disruption of the length of the day. The thrust-fault quake -- in which plates under the Earth's surface moved vertically -- caused mass to be redistributed, said Gross, who works at the Jet Propulsion Laboratory in La Cañada Flintridge.

Riding in school buses in the early morning, then sitting in poorly lighted classrooms are the main reasons students have trouble getting to sleep at night, according to new research. Teenagers, like everyone else, need bright lights in the morning, particularly in the blue wavelengths, to synchronize their inner, circadian rhythms with nature's cycles of day and night. If they are deprived of blue light during the morning, they go to sleep an average of six minutes later each night, until their bodies are completely out of sync with the school day, researchers from Rensselaer Polytechnic Institute reported Tuesday in the journal Neuroendocrinology Letters.

Doctors often wonder if there is a best time of day for cancer patients to receive chemotherapy. Past research suggests there probably is an optimal time based on the body's circadian rhythms. Now a compelling new study offers some biological proof for the idea. Researchers at the University of North Carolina have discovered that chemotherapy is probably most effective at particular times of day when an enzyme system in the body that can blunt the effect of the drugs is at its lowest levels.

AT 6 a.m., the hospital's bright hallway lights flicker on, signaling the start of a new day. Doctors in crisp business clothes appear on their early-morning rounds, and the clang of breakfast carts will soon echo through the unit. For registered nurse Liberty Bunag, however, it's finally time to go home and sleep. She began her shift 12 hours ago with an extra-large coffee and since has consumed a liter of caffeinated soda, more coffee and lots of rice, her personal energy food. Sometimes she and the other nurses on the orthopedic ward of White Memorial Medical Center in Los Angeles practice foreign languages to stay alert, squelching the yawns and drowsiness -- the body's way of protesting this nocturnal activity.

AT 6 a.m., the hospital's bright hallway lights flicker on, signaling the start of a new day. Doctors in crisp business clothes appear on their early-morning rounds, and the clang of breakfast carts will soon echo through the unit. For registered nurse Liberty Bunag, however, it's finally time to go home and sleep. She began her shift 12 hours ago with an extra-large coffee and since has consumed a liter of caffeinated soda, more coffee and lots of rice, her personal energy food. Sometimes she and the other nurses on the orthopedic ward of White Memorial Medical Center in Los Angeles practice foreign languages to stay alert, squelching the yawns and drowsiness -- the body's way of protesting this nocturnal activity.

Unlike plants that turn to face the sun and animals that seem to crave its light, humans have supposedly evolved to the point where we no longer react to changes in light. Not so, according to scientists who see much evidence of light's physical and psychological effects on us. Their research has the greatest bearing on people who suffer from jet lag or certain types of insomnia, who work night shifts or who experience autumnal or wintertime depression because of shorter, darker days.

New research shows that bathing different parts of the body with light, even the knees, can reset your biological clock. "Until we did this study, it was widely assumed that in mammals, including humans, their biological clocks could not be affected by light except through the eyes. So this is quite a surprising result," said chronobiologist Scott Campbell of Cornell University.

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.

Years ago, it used to be standard practice for hospital nurses to leave bright lights on all the time in neonatal intensive care units because it helped the staff better attend to premature infants' urgent medical needs. Over the years, though, researchers found that constant light was stressful for preemies, so many NICUs switched to near-darkness, aiming to mimic the darkness of the womb.