What time is it? Your body knows.

Internal 'clocks' regulate behavioral, psychological rhythms

Internal 'clocks' regulate behavioral, psychological rhythms

March 13, 2006|by JULIE E. GREENE

Ticktock goes the clock, and, as it goes, so goes our sleep, mood and health.

This timekeeper is our internal clock.

The human body has many clocks in its structures and cells, but the master clock is in the suprachiasmatic nucleus region of the brain's hypothalamus, says Dr. Teodor Postolache, a physician and associate professor of psychiatry at the University of Maryland School of Medicine in Baltimore.

This clock establishes behavioral and physiological rhythms called circadian rhythms based on its cycle, which usually lasts more than 24 hours, but less than 25 hours, under constant conditions, Postolache says.

So if a person was kept in a controlled environment such as a cave with no light changes, each day the person would end up going to bed at a later time and waking up at a later time than the person would in real-world conditions, Postolache says.


The hypothalamus helps regulate breathing, heart rate, body temperature, blood pressure, hormone production and other vital body functions, says Lynne Lamberg, co-author of "The Body Clock Guide to Better Health." The suprachiasmatic nucleus is like the chief executive officer of the hypothalamus.

This body clock is influenced by light.

Light travels from the eyes on special nerve pathways to the suprachiasmatic nucleus, says Lamberg, who lives in Baltimore.

Managing exposure to light or certain intensities of light has been shown to help people whose body clocks might get out of whack from jet lag or night-shift work.

People who work night shifts are working at a time the body clock says it's nighttime and would want to sleep.

Several studies, set in labs or real-life conditions, have shown bright light improves alertness at night, Postolache says. Thus, bright light could improve the energy level of night-shift workers.

Night-shift workers could wear dark sunglasses on their way home to control light exposure, helping the body clock adjust and making it easier to get to sleep, according to Lamberg and Postolache.

Because it's more difficult to control exposure to light when traveling through many time zones, Lamberg says people can prepare their body clocks by switching their routines before they leave to fit the destination's time.

Other ways the body clock influences our lives are:

· Adolescents' clocks run on a delayed cycle so their bodies want to go to bed later and wake up later. Because they must get up to go to school early, they often are sleep-deprived, Postolache says.

Some middle schools and high schools start the school day earlier than elementary schools so adolescents have to get up earlier, when it should be the other way around, says Dr. Greg Lyon-Loftus with Mont Alto (Pa.) Family Practice.

If adolescents need to be awake in time for a 7:30 a.m. school start, they need to be in bed by 9 p.m. - an unrealistic bedtime for a teenager, Lyon-Loftus says. "How many teenagers do you know that go to bed at 9 o'clock?"

· Seasonal-affective disorder's winter depression occurs when people have symptoms of depression during the winter months when daylight periods are shorter.

· Daylight-saving time creates a one-hour mismatch between our internal clock and external clock. Moving our clocks ahead one hour in the spring results in less daylight in the morning.

People with seasonal-affective disorder, who were just starting to feel better with the morning daylight, might experience a setback as they lose that early morning light, Postolache says.

The time change in the spring can be harder on people who lose that one hour of sleep, Lamberg says. Many people cannot force themselves to go to sleep one hour earlier. She suggests gradually going to bed earlier, by 15-minute increments, to prepare for the time change.

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