What to Do to Set Your Body Clock : Eating, Sleeping and Exercising on Schedule Keep You Ticking

Health and Fitness News Service

Does anybody really know what time it is? Your body clock knows. With the precision of the finest Swiss watch, it has been keeping time--your time--from the moment you were conceived.

From how fast your blood clots to how many calories you burn, from when your toothache is likely to be most painful to when you’re most likely to fall in love, from when you’re most apt to lose weight or get a raise--virtually every activity in your life is governed by the beat of your internal drummer.

Your body clock, or circadian rhythm (circadian is Latin for “about a day”), plays such a crucial role in your physical and mental health that is has evolved into a science of its own, called chronobiology.

Our body clocks are kept on time by time cues called zeitgebers (German for “time-givers”)--internal and external stimuli that help set the body’s clock. These clues include light, work schedules, food, alcohol, caffeine, exercise, mental stimulation, social activity and many other factors.


For this reason, eating, sleeping and exercising about the same time each day helps keep our body clocks and our bodily functions ticking away on schedule.

Unfortunately, life doesn’t always follow predictable timetables. About 20% of us work the night or evening shift at factories, hospitals and police departments, or rotate shifts--the most disruptive work schedule. Airline pilots and flight attendants who rotate shifts have the most irregular work, sleep and meal patterns of any occupational group, and are more likely to suffer from chronic health problems and premature aging.

Getting a new shift, a new job, a new baby--even a new lover or spouse--can turn your life inside out and your body clock upside down, leaving you with what feels like jet lag--without the jet.

Unless you readjust your body clock to match your new life style, you could suffer from such symptoms as fatigue, insomnia, indigestion, diarrhea, weakness, irritability, stress, lower-back pain, respiratory problems and emotional problems, and be eight times more likely to develop stomach ulcers.

Let’s say you’re a daytime nurse who has just learned that she has been rescheduled to work the graveyard shift in 3 weeks. Your first concern is likely to be how you’ll make it through the night on your feet when you’re used to spending those 8 hours in bed.

The key is to start as early as possible to readjust your three key time cues-- when you go to sleep, when you eat and when you exercise. Don’t expect overnight results. Resetting your time clock so that nighttime really feels like day--and not a hangover--requires a week or more of slowly adjusting your internal clock to its new time frame.

It’s possible to turn your clock ahead by 3 hours a day over the course of 9 days by staying up progressively later and sleeping later each day. Be careful to get enough sleep and create a silent, dark sleeping environment that duplicates nighttime.

If you’ve been bumped to the night shift, start your “day” off with a high-protein breakfast to rev your body into high gear and fuel you through the night.

For “lunch,” choose light, high-protein foods like salad, fish and lean meat. These foods will give you energy without making you sluggish or lethargic. “Dinner” should be a light, high-protein, complex-carbohydrate meal that includes fruit, whole-grain bread and low-fat milk.

To feel like part of the human race, try to eat at least one meal with friends or family--even if they’re eating dinner and you’re eating breakfast.

Exercise is also an important physical, mental and social zeitgeber. Between the time you get home from work and bedtime, relax and unwind with leisure or social activities and light exercise, with friends if possible.

Don’t engage in vigorous exercise before bedtime or you may be too stimulated to sleep.

Understanding your body clock is more than a matter of health. Research indicates that most accidents attributed to human error occur during one of two “zones of vulnerability” when neural functions ebb--from 2 to 7 a.m. and 2 to 5 p.m. A few examples:

- More than half of 6,052 single-vehicle accidents recorded in studies from Texas, Israel and New York occurred between midnight and 7 a.m., peaking between 1 and 4 a.m.

- The Presidential Committee report on the space shuttle Challenger explosion said human error and poor judgment were linked to sleep loss during shift work. Some key managers reported that they had slept less than 2 hours the night before the tragedy.

- Studies show a significant rise in accident rates in the United States during the 2 weeks in which we “spring forward” to daylight-saving time or “fall back” to standard time.

Most people tend to be day people (larks) or night people (owls), as classified by Charles F. Ehret, an authority on circadian rhythms at the Argonne National Laboratory and co-author with Lynne Waller Scanlon of the popular “Overcoming Jet Lag.”

Larks and owls differ because their body clocks operate on slightly different schedules, with owls lagging behind larks by about an hour.

In general, a lark is the proverbial early-to-bed, early-to-rise type who bounces out of bed feeling cheerful and energetic, has a productive morning and begins to wind down in mid-afternoon. By 11 p.m., he’s ready for bed.

Larks tend to be more introspective than owls, to lead controlled, structured lives and to be more achievement-oriented. Because they love structure, their meals are usually balanced and well-regulated. Larks who are overweight are more likely to consume extra calories by snacking between meals than by binging.

Owls are a different species entirely. An owl routinely retires after the “Tonight Show” and is likely to sleep through the 6 a.m. alarm--and until lunchtime if he can.

More likely to crawl than bounce out of bed, and endure rather than experience mornings, owls peak later in the day or in the early evening and don’t begin winding down until about 10 p.m.

Owls are generally more extroverted, social creatures who are natural leaders and who strive to make a lot of money. Because they rise late, they generally skip breakfast, but more than make up for it by binging on favorite foods later in the afternoon and in the evening, when their taste buds are primed.

Despite the wide variances in body clocks and the fact that owls generally lag an hour or so behind larks, a few generalizations about the human body clock hold true:

- Most of us feel best when we’re in sync with the sun--awake during the day and asleep during the night.

- About half of our adrenal hormones are secreted into the bloodstream before we wake up in the morning. Early in the day there is a surge in the production of corticotrophin, a pituitary hormone. Our sense of taste and smell are usually at a low ebb in the morning, when these hormones are at their highest levels.

- The average person’s sense of taste and smell become sharper and more discriminatory as the day goes on, so we’re more likely to be adventurous in our choice of foods at dinner than at breakfast.

- Most of us feel a bit fatigued or lethargic around 4 to 5 p.m., when blood sugar levels are low.

- As body temperature rises and other vital processes pick up pace during the day, most of us start feeling more energetic. We’re at our best when our temperature is at its normal high point.

- At midday or in the early afternoon, most of us are best prepared to handle situations requiring good memory, mathematical skills and hand-eye coordination. We also tend to be physically stronger and faster in the afternoon.

- Moods and attitudes have corresponding highs and lows through the day, affecting what and when we eat. This is particularly true for those who use food to alter their moods.