(The Los Angeles Daily News) -- The teenager who sleeps until noon. The morning person who's perky at the crack of dawn. The worker who has a burst of energy before lunch and then catches a second wind in the early evening.

Most people see these patterns as matters of personality or preference. Experts in circadian rhythms say they're biological, emanating from an internal clock that dictates everything from when we sleep to when we're most productive at work.

Deep in our brains, a clump of cells tinier than a pinhead form the body's clock. Called the suprachiasmatic nucleus, this timing system fluctuates over a 24-hour period and regulates functions both basic and complex, including the secretion of hormones and the ability to learn and remember.

Researchers believe knowledge of how the body clock works can be applied to everyday life. As anyone who's ever worked a night shift or suffered from jet lag knows, turning off the body's clock isn't as simple as hitting the snooze button on the alarm.

"It's a particular problem in industrial society because there's economic pressure to ignore (the) time of day," said Christopher Colwell, associate professor of psychiatry and biobehavioral sciences at UCLA. "Turning on a light will not override this. We muck ourselves up by doing this and by ignoring this powerful biological regulatory system."

Michael Smolensky, author of "The Body Clock Guide to Better Health," adds that circadian rhythms can play a critical role in health, influencing the best time of day to schedule a doctor appointment and when to take medications.

"A great deal of research has been spawned in different directions," said Smolensky, a professor of environmental physiology at the University of Texas at Houston. "If we know there are circadian rhythms, then this has ramifications."

BEATING THE CLOCK

Our internal clocks stay in sync with the world by reacting to morning light. But studies have shown that the timing system continues to work even when a person is left in the dark, though the clock then runs closer to a 25-hour cycle.

Researchers, however, believe circadian rhythms aren't exact, ranging from 23 to 25 hours. The people who run on the faster clock would be the morning people, and those whose clocks are slower would be the night people.

Kristine Bounds turns her body clock around twice a week. As an emergency room nurse at Encino-Tarzana Regional Medical Center, she pulls three consecutive shifts from 7 p.m. to 7 a.m. On her four days off, she reverts to sleeping at night so she can spend her days with friends and family. A 28-year veteran of nursing, Bounds sticks to an eating and sleeping schedule that allows her to make the transition. Naps are an integral part of keeping fatigue at bay, she says.

"There are a lot of people who just can't do it at all," Bounds said. "My mother was a nurse also, and she was able to do it. I don't think heredity has anything to do with it, but I am a stay-up-late, sleep-late person."

Shift workers and travelers often suffer from fatigue, upset stomachs and a lack of concentration. Over the long term, studies have found that shift workers are at higher risk for sleep disorders, peptic ulcers, heart disease and high blood pressure.

From a circadian standpoint, the easiest way to transition to night shifts is for the worker to arrive and leave work at a progressively later hour each week, Smolensky said. How quickly the body's rhythms adjust to a new time zone or work schedule depends on the individual. Some can take up to a week to adjust.

"If you go in a forward direction, that's in sync with the biological clock," Smolensky said. "The same goes for jet lag."

Circadian rhythms are also responsible for the afternoon drowsiness that many workers experience. According to the Massachusetts-based Circadian Technologies Inc., a consulting firm for companies that operate around the clock, the drop in energy happens whether or not you eat lunch. A big meal simply exacerbates the effect.

Besides the postlunch dip, experts say the worst time of all for human performance is between 2 a.m. and 4 a.m. That's not a big deal to the majority of Americans who are sound asleep. But 12 to 15 percent of U.S. workers spend at least part of their time on the night shift.

Circadian rhythms also change pace with age. Teenagers don't stay up late just to be rebellious. Their internal clocks tend to keep them awake until around 1 or 2 a.m., which means they won't get out of bed until noon. By contrast, the elderly tend to go to bed early in the evening and wake up early in the morning, said Sonia Ancoli-Israel, a professor of psychiatry at the University of California, San Diego, and an expert in sleep research.

"If you're in the wrong part of your circadian rhythm, you'll have a hard time falling asleep," she said.

TIME FOR TREATMENT

Sleep and productivity aren't the only areas where being attuned to circadian rhythms can be helpful. From working in the emergency room, Bounds says nurses learn that heart attack patients brought to the ER in the early morning hours are more likely to be severe cases.

"If they come in at that time, we know it's a bad one," she said.

According to the Mayo Clinic, heart attacks and strokes happen most frequently between 7 a.m. and 11 a.m. After getting out of bed, the blood pressure rises, the heart rate increases and the flexibility of the blood vessels is altered - changes that may lead to the increased risk in the morning hours.

Other diseases also show daily rhythms. Inflammatory conditions like asthma, rheumatoid arthritis and hay fever are more likely to flare up overnight. This is because the hormone cortisol, which has an anti- inflammatory effect, is at its lowest levels during sleep, Smolensky said.

Experts in circadian rhythms say that following the natural ebb and flow of circadian rhythms can lead to better diagnosis and treatment.

Doctors ideally would schedule diagnostic tests at times that are in sync with the body clock. UCLA's Colwell notes that people have stronger resistance to allergens in the mornings. So allergen skin tests will provide a more accurate result in the afternoon.

An appointment for glaucoma would be best done in the morning, Smolensky said. Intraocular pressure from glaucoma rises during the sleep cycle. At a morning appointment, the eye pressure will be closest to its highest levels.

Medications also should be tailored to the body clock. Traditionally, scientists have designed drugs with the goal of maintaining a constant level in the body. More recently, with conditions like hypertension and asthma, the notion of a cyclic release in which medication levels change with what the body needs has started to catch on.

Two hypertension medications, Covera-HS and Verelan PM, do just that. The pills are taken at bedtime, but the medication has a slow time release, taking effect toward morning, when blood pressure levels are high. The asthma medication Uniphyl also functions according to biorhythms. Taking the medication at bedtime reduces the likelihood of an asthma attack by 50 percent, said Smolensky, who has done extensive research on circadian rhythms and asthma.

"It's the same daily dose," he said. "The difference is in how it's distributed."

Researchers continue to pursue a range of health topics connected to circadian rhythms. Colwell is using mice to study how circadian rhythms regulate the ability to learn and remember. Ancoli-Israel, the UCSD sleep expert, is running a study that examines the relationship between circadian rhythms, chemotherapy and fatigue in breast cancer patients.

Though there's a growing amount of research to support the application of circadian rhythms in medicine, the practice is still far from common. The concept of homeostasis - that the body remains constant in its biology over time - has long been the standard in medicine. But that's starting to change, Smolensky said.

"We're getting there, but this is a developing science," he said. "I think doctors will accept it and embrace it if they understand the rationale for it. We need to get this into the curriculum in the schools of nursing, medicine and pharmacy. Then doctors can make their own decisions."

Copyright 2002 The Los Angeles Daily News. All rights reserved.