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For several decades, scientists have been accumulating knowledge about circadian rhythms, the daily ups and downs of our metabolic processes. Only recently, however, have they returned to the time honored concept of chronotherapy to help people get well.

Different organs seem to operate on different time sequences. These functions are so regular that medical writer Dunja Voos deems them "clockwork organs." Scientists believe that we have genetically determined clocks that operate many of our hormonal functions, including the secretion of insulin and cortisol, as well as mechanisms that respond to changes in the season, changes in lighting, and changes in our daily activities. Knowing when your body is likely to focus on a particular symptom makes it easier to treat the symptoms of disease.

Brain Rhythms

Knowing when to take a pain reliever in anticipation of a severe headache can make a huge difference in the severity of the subsequent pain. Different kinds of headaches, however, occur at different times of day. Cluster headaches, for example, typically strike during REM sleep, sometime between midnight and three in the morning. If you tend to have cluster headaches, your doctor may advise you to give your child (cluster headaches are most commonly a problem of children) a pain reliever just before you go to bed. 
Migraine headaches tend to strike first thing in the morning, around sunup. At least you can have your treatments handy for early morning use, even if you can't get up in the middle of the night to take them. Men who get migraines tend to experience their symptoms later in the day than women, closer to mid-morning. 

Eye Rhythms

Redness in the eyes is usually worst early in the morning. This is the time pinkeye and conjunctivitis symptoms will be most severe. Dry eyes (caused by conjunctivitis sicca or autoimmune diseases such as Sjogren's syndrome) will tend to be worse later in the day. Using eye drops in the late morning maximizes their effectiveness.

Even Cardiac Arrhythmia Has A Rhythm

Emergency room doctors notice that sudden death, the heart suddenly stopping, is most likely to occur between six in the morning and noon. Heart pain with an EKG signature of a raised ST segment, however, is more common between six in the evening and midnight. Sudden death in insulin-dependent diabetics, however, occurs almost exclusively during sleep.
Chronic heart conditions like congestive heart failure typically get worse during the day and, if they are going to cause a need for emergency treatment, become critical at night. Heart attack (myocardial infarction), nowever, usually occurs during the day, except among people who take a medication in the beta-blocker class to control their heart rhythms.
High and low blood pressure also seem to cycle during the day. During sleep, blood pressure levels are 10 to 25 percent lower than during the day. Both systolic and diastolic blood pressures increase after waking in the morning. As people get "revved up" for their daily activities, especially if they have to exert physical effort under time pressure (running to catch a bus, hurrying to go to an appointment), blood pressure levels reach their peak. This is the reason the blood pressure measurement your doctor takes late in the morning, especially when you had to rush to make the appointment, can be uncharacteristically high.

More Examples Of Chronobiology In Symptoms Of Disease

Whether someone has high blood pressure or not, stroke is more likely to occur during the late afternoon or early evening. Strokes, both ischemic (caused by blood clots) and hemorrhagic (caused by bleeding vessels in the brain) are rare at night. 
Pulmonary embolism (blood clots in the lungs) and deep vein thrombosis (DVT) are most likely between ten in the morning and one in the afternoon. Death from pulmonary embolism, however, is most likely to occur earlier in the morning, after waking up.

Respiratory Rhythms

A dripping nose (rhinorrhea) is one of the more troubling symptoms of colds and seasonal allergies. Runny nose is most likely to occur in the evening, and just after you want to go to sleep, and then again in the morning. The nasal "spigot" gets turned off, usually, during the middle of the day. Knowing this tells you that the best time to take an antihistamine, particularly if it is going to make you sleep, is an hour or two before bedtime.
Cough, on the other hand, is worse during the middle of the day. Decongestants and cough suppressants are most effective when they are taken after breakfast.
Asthma, chronic brochitis, emphysema, and chronic obstructive pulmonary disease tend to follow a course strangely similar to Traditional Chinese Medicine's "time of the lungs," between three and five in the morning. Four in the morning is prime time for asthma attacks. COPD symptoms tend to be worst between midnight and eight in the morning.


At night, the kidneys produce a hormone called vasopressin. This reduces urine production, so we can sleep undisturbed. When there is an urge to urinate at night, there could be a hormonal disturbance, but there is more likely to be a problem with sleep apnea, which forces more blood flow through the kidneys, resulting in greater urine production, urinary tract infection, or, in men, prostate disease.

Gastrointestinal Function

The stomach uses acid to digest food. For that reason, stomach acidity is greater when we have not eaten recently, which for most of us is after midnight. If you are prone to gastroesophageal reflux disease symptoms, the most severe acid burns will come at night. GERD tends to come in "daytime" or "nighttime" patterns, depending on the degree to which anatomical features cause the disease. If the fundamental problem is that there is just too much pressure on the stomach, heartburn and GERD will tend to manifest themselves shortly after eating. If the problem is more hormonal in nature, the symptoms will tend to occur at night.
Gallstones tend to be a problem late at night (after ten in the evening) through the early hours of the morning just after midnight. Ulcers tend to be more of a problem in the late afternoon, especially between four and five o'clock.

Infections And Fever

Viral infections tend to cause higher fevers in the afternoon, especially between four and eight o'clock. Bacterial infections tend to cause higher fever in the morning, especially between six and ten o'clock.

Inflammatory Diseases

The stress hormone cortisol is the body's way of relieving the constant inflammation causes by allergies, arthritis, eczema, and psoriasis. When cortisol levels are lower, especially at night, pain, swelling, itching and redness tend to be worse. Medications should be timed to relieve nighttime symptoms.
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