Biorhythms

Medical Author: William C. Shiel, Jr., MD, FACP, FACR
Medical Editor: Melissa Conrad Stöppler, MD

• What are biologic rhythms?
• How does the "body clock" affects symptoms of illness?
• What are examples of specific diseases affected by biorhythms?
• Angina
• Heart attack
• High blood pressure (hypertension)
• Hay fever (allergic rhinitis)
• Asthma
• Can the "body clock"  affect diagnostic testing?
• Can drug therapy be matched to the "body clock?"
• Chronobiology: marking time, making progress

What are biologic rhythms?

What are biologic rhythms? In essence, 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.

These time-related medical observations, and others still in the exciting process of discovery, are rooted in chronobiology (chronos - time; bios - life; logos - science), the study of biologic rhythms.

How does the "body clock" affects symptoms of illness?

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.

Next: What are examples of specific diseases affected by biorhythms? »

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