The Phoenix Project
An Introduction to Biorhythms
The Pros and the Cons
Last updated Tuesday, April 28, 2009 09:45 AM

The theory of biorhythms is a pseudoscientific theory that claims our daily lives are significantly affected by rhythmic cycles overlooked by scientists who study biological rhythms. Biochronometry is the scientific study of rhythmicity and biological cycles or "clocks," such as the circadian (from the Latin circa and dia; literally, "about a day").

Circadian rhythms are based upon such things as our sensitivity to light and darkness, which is related to our sleep/wakefulness patterns. Biorhythms is not based upon the scientific study of biological organisms. The cycles of biorhythm theory did not originate in scientific study, nor have they been supported by anything resembling a scientific study.

The theory has been around for over one hundred years and there has yet to be a scientific journal that has published a single article supporting the theory. There have been some three dozen studies supporting biorhythm theory but all of them have suffered from methodological and statistical errors (Hines, 1998).

An examination of some 134 biorhythm studies found that the theory is not valid (Hines, 1998). It is empirically testable and has been shown to be false. Terence Hines believes that this fact implies that biorhythm theory "can not properly be termed a pseudoscientific theory."

However, when the advocates of an empirically testable theory refuse to give up the theory in the face of overwhelming evidence against it, it seems reasonable to call the theory pseudoscientific.

For, in fact, the adherents to such a theory have declared by their behavior that there is nothing that could falsify it, yet they continue to claim the theory is scientific.

Biorhythm theory is based more on numerology, testimonials and the Forer effect, mass media hype, and intuition than on scientific study.

The theory originated in the nineteenth century with Wilhelm Fliess, a Berlin physician, numerologist and good friend and patient of Sigmund Freud.¹  Fleiss was fascinated by the fact that no matter what number he picked he could figure out a way to express it in a formula with relation to either 23, 28 or both.²   The latter number he associated with menstruation and thus when he was convinced that all the world is governed by 23 and 28, he called the 28-day period "female" and the 23-day period "male."

In 1904, several years after Fliess's discovery, Dr. Hermann Swoboda of the University of Vienna, claimed he discovered these same periods on his own. In the 1920s, Alfred Teltscher, an Austrian engineering teacher, added the 'mind' period of 33 days, based upon his observation that his students' work followed a 33-day pattern.

The theory was popularized in the 1970s by George Thommen (Is This Your Day? How Biorhythm Helps You Determine Your Life Cycles) and Bernard Gittleson (Biorhythm--A Personal Science).

Neither book provides scientific evidence for biorhythms. They consist of little more than speculation and anecdotes.

However, by now the static idea of periods was replaced with the dynamic notion of cycles, which are now known as the physical, emotional and intellectual cycles.

Interestingly, not only did the "female" period become the emotional cycle, but both men and women are said to share the same physical and emotional cycles of 23 and 28 days respectively. One might have expected that, given the different hormonal natures of males and females, the sexes might have at least some unique and distinct rhythmic cycles.

New cycles have been added in recent years. There is the 38-day intuitional cycle, the 43-day aesthetic cycle, and the 53-day spiritual cycle. Others claim there are cycles that are combinations of the three primary cycles. The passion cycle is the physical joined with the emotional cycle. The wisdom cycle is the emotional joined with the intellectual cycle. And the mastery cycle is the intellectual joined with the physical cycle.

However many cycles there are, the function is the same: to predict what kind of day one is likely to have.

Generally speaking, the more positive a cycle is at any given point in time, the better one is able to interact in that arena. For example, high emotional level tends to mean that a person is more stable, is better able to make relationship decisions, and so on. This is not to say that when the cycle is in the negative range that the person is not doing well in that arena, rather, it means that it is harder to do well. --Plan exams when your Intellectual cycle is high. [Facade]

At the moment of birth, according to the theory, the biorhythmic cycles are set to zero. Knowing your birthday, the number of days you have lived and where in each cycle you are can be determined for any given day. A biorhythmic chart for July 24, 1998, for someone born four days earlier would look like this:

According to the theory, when certain points on the cycles are reached a person may enjoy special strength or suffer special weakness.  "Switch point days," when cycles cross the zero line on the ascent or descent, are "critical" days.

Performance on critical days is supposedly very poor. It has even been predicted that people are especially accident prone on critical days. This empirical claim is easily testable. It has been tested and shown to be false.

However, any cycle with an odd number of days does not have an exact day in the middle, a fact which has led some "experts" to do some slippery math.

For example, one "scientific study" said to support biorhythm theory claims that something like 60% of all accidents occur on critical days but critical days make up only 22% of all days.

If true, this statistic would not likely be due to chance and biorhythm advocates could justifiably claim their theory had been confirmed by this data.

However, biorhythmists include both the day before and the day after a switch point day as "critical" days. Thus, an accurate statistic would be something like about 60% of all accidents occur on about 60% of all days, which is to be expected by chance (Hines).

In any case, according to the theory, critical days are days you want to know about in advance so you can prepare for them. For example, if you are scheduled to take a test that will measure your thinking ability, make sure you do not take the test on a day when your intellectual cycle is at a critical or a low point.

Of course, to do well one must also get a good night's sleep, be generally healthy, eat properly, and study, but those preparations will do you no good if your intellectual cycle is not in the right spot.

On the other hand, if you are a long distance runner, try to pick your next race date so that you are at a peak on your physical cycle. Of course, you must train properly, eat well, get sufficient rest, be healthy, etc., but these will not suffice if your physical cycle is at the wrong point.

The worst day of all, according to the classical (3-cycle) theory, is the "triple critical," the day when all three cycles are at a  switch point.

Next worst is the "double critical", when two cycles meet at the switch point. As you can imagine, it gets very complicated tracing all these cycles on their ascents, descents, switch points, etc.

But it does not take a mathematician to figure out that it is going to be easy to find cases that fit the theory. For example, the physical cycle is 23 days long. That means that every 11.5 days is a physical cycle switch over day.

So, the odds of, say, having a heart attack on a given physical switch over day are about 1 in 11. Most people would agree that having a heart attack is having a bad physical day.

One valid empirical test of the theory would be to collect data on heart attack victims and see if significantly more than 9% (1 out of 11) had their heart attacks on physical switch over days. Instead, the usual evidence given by believers is an anecdote about Clark Gable or someone else who had a heart attack on a switch over day.

There are thousands of heart attack victims each year and 1 out of 11 of them would be predicted by chance to have the attack on a switch over day. So, finding several individual cases of people who have serious physical problems on a critical physical day is to be expected, not wowed at.

The ho-hum response that anecdotes such as the Clark Gable story should evoke from a reasonable person should put one to sleep when you consider that biorhythmists generally count the day before and after a critical day as being just as bad as critical days. This means that 6 out of every 23 days (26% of our days) are danger days for the body.

Thus, the odds are about one in four that any given person who has a bad physical day is at a "critical" point. Anecdotes of people having bad physical days are particularly inconsequential given such odds. A meaningful test of the theory might be to study heart attack victims. If significantly greater than 25% of the sample have attacks on a critical days, then you have a scoop.

Another typical but useless test of the theory is to keep track of how accurate the theory is by charting each day and keeping a diary of your days.\

Actress Susan St. James, a fervid believer in biorhythms, once described on a television talk show how she had done this. If her chart predicted a low emotional day, she was upset that day. If her chart predicted a physical high, she felt great that day. On a day when her intellectual cycle was at a low, she couldn't think straight about anything. In some circles this is known as the self-fulfilling prophecy, the power of suggestion or subjective validation. Whatever you call it, it isn't science.

To demonstrate the folly of using subjective validation to count as support for biorhythm theory, James Randi had George Thommen, president of Biorhythm Computers, Inc., do a biorhythm chart for Randi and his secretary. One of the listeners to Randi's radio program was selected for an experiment. She was to be given her own personal chart and she was to keep a day-by-day diary for two months and to rate her chart for accuracy. She reported that the chart had been "at least ninety percent accurate." The devious Randi had actually sent her his own chart. He told the subject that he had done this by mistake. She agreed to check her diary with her real chart, which Randi gave her. She reported that the new chart was even more accurate than the other one. Actually, she'd been given Randi's secretary's chart. This kind of data retrofitting is common among believers in such pseudosciences as astrology, graphology and biorhythms. In fact, similar tests of subjective validation, with identical results, have been done on astrological charts and graphological readings. Randi's deception, of course, was not intended to disprove biorhythms, but to call attention to the problem of subjective validation, something consistently overlooked by devotees of astrology, graphology and biorhythms.

Biorhythms is a pseudoscience because there have been several meaningful tests of the theory, all failing to support it (Hines, 1991), yet its advocates refuse to give up the theory. Advocates of this theory have more ad hoc hypotheses to explain away disconfirming evidence than Galapagos has islands. My favorite is the hypothesis that some people are arrhythmic some or all of the time. Any contrary case can be explained away by reference to the case being arrhythmic.

Another favorite ad hoc hypothesis concerns Thommen's claim that he could predict with 95% accuracy the sex of a child by the biorhythms of the mother. If, during conception, the mother's physical (masculine) cycle was at a high point, a boy was likely. If, during conception, the mother's emotional (female) cycle was at a high point, a girl was likely.

A study done by W.S. Bainbridge, a professor of sociology at the University of Washington, concluded that using the biorhythm theory your chances of predicting the sex of the child were 50/50, the same as flipping a coin. A defender of the theory suggested to Bainbridge that the cases where the theory was wrong probably included many homosexuals, who have indeterminate sex identities!

Footnotes

¹ Freud's letters to Fliess were preserved, much to Freud's dismay. They were first published in English as Origins of Psychoanalysis: Letters to Wilhelm Fliess Drafts and Notes, 1887-1902. Edited by Marie Bonaparte, Anna Freud and Ernst Kris, translation by Eric Mosbacher and James Strachey (London: Imago Pub. Co., 1954). A more recent translation by Jeffrey Moussaieff Masson is available: The Complete Letters of Sigmund Freud to Wilhelm Fliess, 1887-1904 (Cambridge, Mass.: Belknap Press of Harvard University Press, 1985). Fliess's masterpiece is entitled The Rhythm of Life: Foundations of an Exact Biology (Leipzig: 1906). There is a discussion of Freud, Fleiss and biorhythms in Frank Sulloway's Freud: Biologist of Mind (Cambridge, Mass:; Harvard University Press, 1993).

² How did Fliess come up with his theory about the magic of the numbers 23 and 28?   Martin Gardner writes:

Fliess's basic formula can be written 23x + 28y, where x and y are positive or negative integers. On almost every page Fliess fits this formula to natural phenomena, ranging from the cell to the solar system....He did not realize that if any two positive integers that have no common divisor are substituted for 23 and 28 in his basic formula, it is possible to express any positive integer whatever. Little wonder that the formula could be so readily fitted to natural phenomena! [Gardner pp. 134-135]

More Resources 

Books and Articles

Gardner, Martin. Science: Good, Bad and Bogus (Buffalo, N.Y.: Prometheus Books, 1981), ch. 11, "Fliess, Freud, and Biorhythm."

Hines, Terence M. "Comprehensive Review of Biorhythm Theory," Psychological Reports, 1998, 83, 19-64.

Hines, Terence. "Biorhythm Theory: A Critical Review," in Paranormal Borderlands of Science,  ed.  Kendrick Frazier (Amherst, N.Y.: Prometheus Books, 1991).

Hines, Terence. Pseudoscience and the Paranormal: A Critical Examination of the Evidence (Buffalo, NY: Prometheus Books, 1990).

Randi, James. Flim-Flam! (Buffalo, New York: Prometheus Books,1988), ch. 8, "The Great Fliess Fleece."

Websites

• Biorhythmic chart generator

• Facade biorhythm chart generator

Biorhythm chart for a 4-day-old born on 7/20/98

The line going through the middle is the zero line. A cycle is said to be in a positive phase when above the zero line and in a negative phase when below the zero line. A cycle begins in an ascent for the first fourth of a cycle, then half of the cycle is in descent, then the last quarter of the cycle ascends back to the zero line. The cycles repeat until you die. Should you live to be something like 58 years and 66 days old, you will reach the point at which the physical, emotional and intellectual cycles return to the same point on the zero line. For some, this is a moment of  "rebirth."

According to the skeptics, when the anecdotes don't fit the theory, biorhythmists are likely to change the theory. For example, one of the more common ways to defend the theory has been to point out that great feats occur when high in a cycle. Defenders of the theory commonly cite the example of Mark Spitz (born 2/10/50) being in a high physical and emotional phase when he won seven gold medals in the 1972 Olympics.

Biorhythm chart for Mark Spitz (9/5/72)

Note how Spitz's emotional and physical cycles converged on September 5, the day of the Munich massacre. Coincidence? Not to inquiring minds. No doubt this is evidence of synchronicity. Note, too, that his intellectual cycle was very low during this period. Why not conclude that he did so well physically because his mind was inactive. Thus, he was not distracted by doing any serious thinking, a known hindrance to athletic performance. Of course, the simplest theory is that he did so well because he was a damn good swimmer! Those of a logical bent might use Occam's razor to reject biorhythms in favor of this simpler explanation.

However, Reggie Jackson, who was inaugurated into Baseball's Hall of Fame and was born on May 18, 1946, had the greatest day in his brilliant career on October 18, 1977. On that day he hit three consecutive home runs on three consecutive pitches off three different pitchers to help the New York Yankees win the game and the World Series against the Los Angeles Dodgers. Jackson's cycles were all in the low end of their negative phases on that day.

Biorhythm chart for Reggie Jackson (10/18/77)

Russ Streiffert has an explanation: "Studies have shown that location in the graphic data may be less important than trend or which way your [sic] going. This is a dynamic interpretation as opposed to earlier views.  Briefly starting at the bottom of the graph we have increasing resource discharge (available)...then maximum discharge across the center line...then decreasing discharge approaching the top. Starting back down we have increasing  recharge (unavailable)...maximum recharge across the center line...then decreasing recharge approaching the bottom. In the graph above, notice how Mr. Jackson's resources appear charged (available) and synchronized on October 18, 1977. While this does not constitute proof that these cycles contributed to his achievements, it appears to be an excellent correlation and is certainly not  disproof. " The studies that have shown this are not cited by Mr. Streiffert.

So, when the data seems to conflict with what would be predicted by the theory, we are to engage in a new kind of interpretation. Reggie Jackson was not in a negative phase of all cycles; he was "charged and synchronized." We are to think in terms of recharging our energy as we ascend in a cycle, and discharging energy as we descend (or is it the other way around?). In this dynamic and energetic view, even days in the negative phase of a cycle can be good and days in the positive cycle can be bad and vice-versa, depending upon whether they are ascending or descending, charging or discharging, available or unavailable. Such constructions may make it impossible to refute the theory, but they render it untestable and so slippery as to be of little use for predicting the future. What was a pseudoscientific theory because its advocates continued to support it even though it failed all scientific empirical tests, is now a pseudoscience because it claims to be a scientific theory but it is not empirically testable. Everything can be made to fit the theory, even contrary readings such as those of Mark Spitz and Reggie Jackson, who deserve more credit for their accomplishments than biorhythm theory can provide.

Below are two bio-rhythm charts for both my wife and me. This program is based on the western scientific theory of biorhythms, and contains additional features based upon oriental philosophy.

I am a bit dubious about the "extra" bio-rhythms because they are not a part of the traditional calculations, but have been added by who-knows-who to make a product more attractive to buyers who may think they're getting more than others offer ... when in fact these "extras" may be totally meaningless. What "oriental philosophy" does this refer to?

You can click on the links and get your own bio-rhythms, and the code to put on a web page (these are called "widgets") so you can keep up with it. This is nice if you create your own Start Page - the one that loads up when you start your browser.

The company that offers this widget also offers a "free" downloadable bio-rhythms program at Whitestranger.com.
http://www.whitestranger.com/.

I'm sure you can also find others on Google. Just remember that "free download" does not mean "free software".

They are not infallible - but then neither is medical science or physics or astronomy or chemistry. With all disciplines, the rules are always changing. As we learn more, what applied yesterday isn't applicable today or tomorrow.

I found the Reggie Jackson example above very compelling, but that example itself doesn't exactly hit a home run - or three. It's quite possible to summon the willpower and determination to overcome tremendous odds.

And today, of course, with all the stories about steroids, you never know what may be responsible for that burst of energy.

Like anything else, bio-rhythms can be subject to misinterpretation and misunderstanding, even by their respective "experts." And people can become obsessed with bio-rhythms or astrology or anything else - yes, even energy healing - to the point that it becomes unhealthy.

In medicine, a drug will work well for one person, but not the next. In many studies, the placebo ("sugar pill") works as well or better than the drug tested.

Does that speak to the ineffectiveness of the drug or the power of suggestion that gets such astounding results for a simple sugar pill?

Now that we've dealt with the critics' opinions, let's take a look from the other side.

What are biologic rhythms?
Source: MedicineNet.com

What are biologic rhythms? In essence, even looked at from the traditional medical perspective, they're the rhythms of life. All forms of life on earth, including our bodies, respond rhythmically to the regular cycles of the sun, moon, and seasons.

For example, as night turns into day, vital body functions, including heart rate and blood pressure, speed up in anticipation of increased physical activity. These and other predictable fluctuations in body function, taking place during specific time cycles, are our biologic rhythms. They are regulated by "biologic clock" mechanisms located in the brain.

Although biologic rhythms can be "reprogrammed" by environmental influences (such as when a person regularly works the night shift and sleeps during the day), they are genetically "hard-wired" into our cells, tissues, and organs.

Medical chronobiologists have found that biologic rhythms can affect the severity of disease symptoms, diagnostic test results, and even the body's response to drug therapy.

Now these investigators are working to discover how the rhythms of life can be used to improve the practice of medicine - and your health.

Now, technically, biologic rhythms are not the same as bio-rhythms. Biologic rhythms are a natural phenomena that stand by themselves and can be observed, studied and measured.

Biologic rhythms, or biorhythms, are how our bodies respond to the regular phases of the sun, moon, and seasons. A medical chrono-biologist studies how the "body clock" or biorhythms affect diseases such as heart disease, arthritis, asthma, allergies, and how the body clock responds to treatment of diseases and conditions at different times of the day.

While bio-rhythms can, so to speak, be "measured", bio-rhythms, as popularly used, are more of an interpretation of what those biologic rhythms might mean in terms of mental, physical or intellectual/emotional guidance and planning.

Also, as discussed here, biologic rhythms have more to do with the different times of the day than with the days of the month.

So the two are closely intertwined, but still somewhat different.

Among the various biologic rhythm cycles that medical chronobiologists study, the 24-hour day/night-activity/rest cycle is considered a key chronobiologic factor in medical diagnosis and treatment. Formally known as the circadian rhythm, it's also referred to as the "body clock."

Why is the 24-hour body clock so important?

Because so many of our normal body functions follow daily patterns of speeding up and slowing down, intensifying and diminishing, in alignment with circadian rhythm. Interestingly, so do the symptoms of a number of chronic disorders:

Allergic rhinitis: (nasal inflammation associated with hay fever) Symptoms of sneezing, runny nose, and stuffy nose are typically worse in the early waking hours than later during the day.

Asthma: In most patients, symptoms are more than 100 times as likely to occur in the few hours prior to awakening than during the day.

Stable angina: Chest pain and electrocardiographic (ECG, EKG) abnormalities are most common during the first 4 to 6 hours after awakening.

Prinzmetal's angina: ECG abnormalities are most common during sleep; chest pain can occur even while at rest.

Heart attack: Heart attack most commonly occurs in the early waking hours.

Stroke: Strokes most commonly occur in the early waking hours.

Hypertension: The highest blood pressure readings typically occur from late morning to middle afternoon; lowest occur during early sleep. Therapy now exists that works with your body clock; consult your physician about this treatment. Clinical studies are underway to further this research.

Rheumatoid arthritis: RA symptoms are most intense upon awakening.

Osteoarthritis: Symptoms of osteoarthritis worsen in the afternoon and evening.

Ulcer disease: The pain typically occurs after stomach emptying, following daytime meals, and in the very early morning, disrupting sleep.

Epilepsy: Seizures often occur only at particular times of the day or night; individual patterns differ among patients.

I recently read a study (and saw it several network news broadcasts) that strongly shows a large spike in heart attacks with the artificial time change we know as Daylight Savings Time.

The attacks and fatalities spike up when we have to get up an hour earlier, and spike down when we get that extra hour of sleep.

The rest of the world (except humans) often sleep and wake up by the sun, going to sleep when it gets dark and waking up when it starts to get light.

Not humans, though. They have to party all night, drag themselves from sleep in a zombie stupor and stumble around for up to an hour before it's even safe to speak to them or look them in the eye. Strange species!

Personally, I hate alarm clocks and will not use them unless absolutely necessary. One can tune into their own bio-rhythms (circadian) and wake up naturally, even at varying times.

I always audibly repeated out loud the time I have to get up, whether it's 5 am or 8 am. And about 98% of the time I do so without any problem.

Alarm clocks are a sudden, violently rude and physiologically traumatic invasion of our natural sleep cycles. Perhaps we'll offer a little "inner training" later in this site so you, too, can live without an alarm clock.

Early morning is my favorite time. The world is quiet and still, not even the birds have started singing yet. It is a time for meditation, prayer and wonderment at the world around around us.

What are examples of specific diseases affected by biorhythms?

Angina

Angina is chest pain or pressure due to an insufficient supply of oxygenated blood to the heart muscle.

• Oxygenated blood is normally delivered to the heart muscle by arteries to the heart (coronary arteries).
• Inadequate oxygenation of heart muscle (ischemia) can occur because of either narrowing or spasm of the coronary arteries.
• Narrowing of the coronary arteries (coronary artery disease or CAD) is usually caused by arteriosclerosis (cholesterol deposits on the inner wall of the arteries).
• In patients with narrowed coronary arteries, factors that increase work demand and oxygen consumption of the heart (such as exercise, excitement, increased blood pressure and heart rate) can precipitate heart muscle ischemia and angina.

Patients who develop angina only during stress or physical exertion have stable, exertional angina. When a coronary artery becomes critically narrowed, heart muscle ischemia or angina can occur with minimal or no exertion. These patients have unstable angina, and are at imminent risk of heart attack (myocardial infarction). A heart attack occurs when a diseased coronary artery becomes completely obstructed by a blood clot, leading to irreversible death of heart muscle. During the early hours of a heart attack, irregular heart rhythms can occur which commonly cause sudden cardiac death.

Heart ischemia resulting in angina can be caused by spasm of the coronary arteries. This is a rare condition called vasospastic angina (also known as Prinzmetal's angina) and is not associated with exertion.

It has been known for some time that the symptoms of ischemic heart disease are more common in the morning hours than at any other time of day.

• Patients experience episodes of stable angina with lower levels of exertion in the morning than in the afternoon.
• The occurrence of episodes of vasospastic angina is higher in the morning than in the afternoons.
• In patients with CAD, electrocardiogram (ECG) changes indicative of heart muscle ischemia are seen more frequently in the morning than in the afternoon.

Heart attack

Over one million Americans suffer a heart attack annually. Over four hundred thousand of these heart attack victims die as a result. Many of the heart attack deaths are due to sudden ventricular fibrillation occurring before the patient can reach any medical assistance or the emergency room. Ventricular fibrillation and other heart electrical disturbances can be treated with medications once the patient reaches the hospital. Therefore, 90% to 95% of those heart attack patients who make it to the hospital survive.

Heart attack (myocardial infarction) is the irreversible death of heart muscle due to complete blockage of a coronary artery, usually by a blood clot forming on a cholesterol plaque.

• A coronary artery is an artery supplying blood to the heart muscle.
• A cholesterol plaque is an abnormal, hard thick deposit on the artery wall.
• The condition whereby cholesterol plaque deposits on coronary arteries is called coronary artery disease (CAD).
• CAD leads to narrowing of these coronary arteries, thus impairing the normal oxygen supply to the heart.
• Coronary artery narrowing can cause angina, chest pain or pressure due to an insufficient supply of oxygenated blood (ischemia) to the heart muscle.
• During a heart attack, heart muscle dies when a diseased coronary artery becomes completely blocked by a blood clot. Heart attack can cause chest pain, heart pump failure, and electrical disturbances in the heart.
• Electrical disturbances in the heart can cause ventricular fibrillation (a chaotic heart rhythm). A heart undergoing ventricular fibrillation simply quivers, and is incapable of pumping oxygenated blood to the rest of the body and the brain. Permanent brain damage usually occurs unless oxygenated blood is restored to the brain within minutes.

Numerous studies, including the classic Framingham study, have shown that the incidence pattern of sudden cardiac death parallels those of hypertension, heart muscle ischemia, angina, and heart attack - a 70% greater risk between the hours of 7 a.m. and 9 a.m., compared to the rest of the day.

Stroke resulting from ischemia occurs more frequently in the morning than at any other time of day. Like heart attack, ischemic stroke refers to permanent death of brain tissue because of blockage of the artery supplying blood to the brain, usually by a blood clot.

High blood pressure (hypertension)

Hypertension or high blood pressure is a silent killer. Early high blood pressure produces no symptoms or discomfort. However, untreated long-term high blood pressure can lead to strokes, heart diseases, kidney disease, and eye damage. Medical scientists now know that a person's blood pressure varies according to the time of day (circadian rhythm). Such variations may have important implications in the diagnosis, treatment, and monitoring of patients with high blood pressure.

It is important to understand a critical distinction: Circadian rhythms do not cause clinical hypertension in normotensives (people with normal blood pressure). Circadian rhythms do, however, result in a cyclic worsening of hypertension in hypertensive patients.

In the majority of individuals - normotensive and hypertensive - blood pressure rises rapidly in the early morning hours, the time when most individuals wake up and begin their day. This morning rise in blood pressure is not caused by the act of getting out of bed and beginning activity. It is a genetically preset system that automatically increases a person's blood pressure at that time.

For example, if a person goes to sleep at around 10 p.m., beginning in the very early morning - sometime between 3 a.m. and 5 a.m. – the blood pressure begins to rise and continues to rise through the morning.

This increase, which is accompanied by an increase in heart rate, corresponds to the following biologic changes, which are also governed by circadian rhythms:

• Increased secretion of catecholamines, particularly norepinephrine, into the bloodstream.
• Increased plasma renin activity.

Catecholamines, norepinephrine, and renin are natural hormones produced by the kidneys and adrenal glands (small glands located near the top of both kidneys). These hormones cause tightening of blood vessels in the body (vasoconstriction). Vasoconstriction causes resistance to blood flow and elevates blood pressure.

In the late morning or early afternoon, the natural rise in blood pressure reaches its peak. After that, blood pressure declines, falling 15 to 20 mmHg between about 8 p.m. and 2 a.m., the time at which blood pressure is normally at its lowest point.

The blood pressure pattern just described is typical of some individuals, whether the individual is hypertensive or normotensive. These people are referred to as "dippers." In other individuals (called "nondippers"), there is no nightly decline in blood pressure. The blood pressure in these people remains high, even during sleep.

Disease of the heart and blood vessels (cardiovascular disease), including hypertension and the syndromes of ischemic heart disease (angina, heart attack, sudden death), also follow circadian rhythms. This pattern makes sense when you consider that heart rate and blood levels of enzymes and catecholamines that strongly influence blood pressure and heart function follow circadian rhythms.

Hay fever (allergic rhinitis)

Allergic rhinitis (hay fever) is a very common condition, affecting 17.6 million Americans annually. The symptoms of allergic rhinitis (sneezing, runny nose, nasal congestion, and itchy eyes) occur when an allergic individual is exposed to allergens. Allergens are tiny proteins that stimulate the allergic reaction. Common allergens include:

• pollens from ragweed, trees, and grasses;
• mold spores;
• animal proteins; and
• mites.

The best way to treat allergic rhinitis is to avoid the allergens. Skin testing is often performed to identify the allergens which cause allergic reactions in a given individual. Scientists now believe that the symptoms of allergic rhinitis, and even the skin testing results, can vary according to the time of day.

For sufferers of allergic rhinitis, the major symptoms of sneezing, runny nose, and stuffy nose are typically worse upon arising than during the middle of the activity span of a given day.

Asthma

Asthma is a common breathing problem, affecting 16.1 million Americans. Asthma is a disease of the lung airways (bronchi). Narrowing of the openings of the airways (caused by spasm, swelling of the tissue lining, and/or mucus accumulation) can lead to shortness of breath, wheezing, or coughing. 

Causes of asthma attacks include:

• allergies,
• cold air,
• air pollutants,
• drugs,
• cigarette smoke,
• molds,
• exercise, and
• infections.

Asthma attacks (rapid worsening of symptoms) typically occur in episodes. Intervals between attacks can be days, weeks, or years. With severe asthma, attacks can occur daily. Scientists now believe that asthma attacks vary according to the time of day.

The occurrence of asthma attacks is not random during the day. Asthma symptoms are frequently worse at night (nocturnal) for a majority of asthma sufferers. A group of active asthma patients recorded the occurrence of acute asthma attacks, manifested by dyspnea (difficulty breathing) and wheezing, during a medication trial. 

The incidence of asthma attacks was more than 100 times greater during nighttime sleep, especially around 4 a.m., than it was during the middle of the day.

Can the "body clock"  affect diagnostic testing?

The body clock's powerful influence can also be seen in the way it affects diagnostic test results. These results can vary significantly, possibly producing inaccurate readings, depending on the time of day when a test is done.

Consider how the body clock affects blood pressure. Blood pressure isn't constant throughout the day and night; it normally rises in the morning, remains elevated during the day and early evening, and decreases to its lowest level during sleep. So a single reading taken during the day may not give a true picture of whether blood pressure is within the normal range or requires treatment. Some doctors now ask patients to wear special monitoring devices that provide a complete 24-hour blood pressure pattern by recording blood pressures a number of times during the day.

The body clock also affects skin testing for allergies. Results are lower in the morning, considerably higher in the evening, and greatest just before bedtime.

The body clock may complicate testing for asthma severity. Airway patency, or degree of openness, is poorest during the night and best during midday and evening. The same is generally true for forced expiratory volume and peak expiratory flow readings, which can be up to 50% higher at midday and in the afternoon than overnight or when the patient wakes up. Unless these circadian rhythms are taken into account, daytime evaluation of asthma patients could result in underestimating the severity of the disease.

What's being done to help doctors obtain the most accurate results from diagnostic tests likely to be affected by the body clock?

Just heightening their awareness of the problem helps. In addition, medical chronobiologists are working to develop test interpretation guidelines for doctors that take circadian rhythms into account.

Can drug therapy be matched to the "body clock?"

The time of day also can affect the way our bodies respond to medical therapy, especially drug therapy. Investigators working in a special area of chronobiology, called chronotherapeutics or chronotherapy, are studying these effects. Their goal is to come up with new medications, or improve existing ones, that make the most of what we know about how the body clock works.

Already there is evidence that taking medication "by the clock" helps the drugs work better and reduces their side effects. Currently, some doctors are prescribing nighttime administration of medication for patients with ulcer disease or asthma (which worsen at night), rheumatoid arthritis (which worsens in the early morning hours), and high cholesterol levels (most of the body's cholesterol production occurs at night). For patients with osteoarthritis, which worsens in the afternoon and evening, some doctors are prescribing midday medication.

Drugs that may be given "by the clock" include corticosteroids, nonsteroidal antiinflammatory drugs (NSAIDs), antihistamines, theophyllines, and anticancer drugs.

These lists are growing as chronobiology, chronotherapy, and the diagnostic and treatment methods derived from them are slowly accepted by the medical community. However, the broad acceptance of chronobiology in medicine is expected to take (excuse the expression) time.

Chronobiology: marking time, making progress

Although chronobiology is not new to medical science, it's still in the process of being accepted by the medical community. That's because most doctors are not taught about chronobiology - in fact, they are taught something that seems to contradict it!

What are doctors taught?

Homeostasis - the concept that body functions are in a constant "steady state" throughout the day and night, and that the goal of treatment is restoring or maintaining this "steady state." Even the treatment itself may have this goal, for example, a prescribed drug is given in a way ("every 4 hours") that theoretically will ensure a steady level of it in the patient's bloodstream. Obviously, this view contrasts sharply with diagnosing and treating illness chronobiologically - "by the clock."

Fortunately, although chronobiology is not yet taught in medical schools, doctors are increasingly taking biologic rhythms into account in diagnosing and treating illness. They are recognizing that whereas homeostatic mechanisms keep the body functioning continuously on a moment-to-moment basis (for example, by maintaining breathing and heartbeat), biologic rhythms program the body "in advance" for coping with its predictably changing needs, such as varying energy requirements, during specific time cycles.

The time is coming, medical experts say, when chronobiology, and particularly the body clock, will play a vital role in many areas of medical practice. In some of those areas, as we've seen, that time is now.

If you are taking medication for a medical condition, consider keeping a record of the timing and intensity of your symptoms for a few days and showing it to your doctor; he or she may want to adjust your therapy to align more with your body clock. Who knows, maybe now is your time to get more into the rhythm of life!

References:

• The right time? Chronopharmacology - a new science. Nursing RSA Verpleging. 1992;7:23-27. Pharmacology.

• Smolensky MH, D'Alonzo GE. Medical chronobiology: concepts and applications. Am Rev Respir Dis.1993;147:S2-S 19.

• Time of day medicine dose is taken may boost its efficacy, cut toxicity. JAMA. 1996;275:1 143-1 144. Medical News & Perspectives.

• American Heart Association; "Know the Facts, Get the Stats 2007."

• Centers for Disease Control, National Center for Health Statistics; "Allergies/Hay Fever."

• Centers for Disease Control, National Center for Health Statistics; "Asthma."

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Last updated Tuesday, April 28, 2009 09:45 AM
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