Illness and Medications
Susceptibility to diseases also may vary at different times of the day, month, or year figure For example, circadian variability has been observed in the onset of allergies, dermatitis, myocardial infarction, cerebral hemorrhage, as well as pain from dental caries, rheumatoid arthritis, and osteoarthritis of the hip and knee. Monthly rhythms exist for the incidence of urticaria hives related to immune system dysfunction as well as bacterial and viral infections in women figure Both circadian and monthly rhythms have been observed for asthma, epilepsy, migraine headache, and bacterial/viral infections see figure Regular annual cycles also have been verified for upper respiratory infections, nonrespiratory infections chicken pox, mumps, rubella, sexually transmitted diseases, and certain birth defects congenital dislocation of the hip. These seasonal
The onset of fever in women, signaling bacterial and viral infections. Top panel circadian rhythm: Bacterial fevers are more common in the morning, whereas viral fevers occur more often in the evening. Bottom panel circamensual rhythm: Bacterial infection is more likely around ovulation, whereas viral infection is more likely around menstruation.
Reprinted from differences in the incidence of disease may be linked with the production and function of hormones. For example, there is a striking association of the annual rhythm of adrenal gland activity which peaks in the spring season with a the annual peak in the incidence of pneumonia and influenza, and b rhythms of immune status.
Even the effectiveness of medications may be different at different points within a day or month. Pharmacologic studies have shown this to be true for aspirin, acetaminophen, ethyl alcohol, diazepam, corticosteroids prednisone, methylprednisolone, cardiovascular drugs digitalis, atenolol, propranolol, antihistamines, diuretics, and antibiotics erythromycin, ampicillin. This occurs, in part, because the amount of a medication that is absorbed into the bloodstream, the amount that is excreted, and the dynamic changes in the plasma concentration all vary. In addition, some drugs psychiatric medications such as lithium actually may lengthen circadian and ultradian rhythms. Thus, it appears that most drugs may produce differential effects depending on the timing of administration.
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Windows of Optimal Performance
Observations of athletes, who are required to perform optimally while under great duress and whose performance is easily measured in terms of time, distance, strength, or points scored, provide valuable insights regarding human performance at different times of the day. Such studies have shown that the majority of performance-critical circadian rhythms are optimal in the afternoon. Table which was compiled from three sources, shows that many physiological and psychological factors peak between the times of : P.M. and : P.M. You should realize, however, that this table presents an average time of day for each factor and that differences in circadian rhythms exist between athletes larks are different from owls in epinephrine secretion, psychological mood, and activity patterns. Also, the unique requirements of each sporting event or work task dictate how each factor in tablealters performance. For example, some activities require small muscle coordination and visual acuity more than others.
Coaches and supervisors can identify the optimal time of day for each athlete by keeping detailed records of previous performance during training sessions and competition. Also, the average athlete can determine his or her own peaks, valleys, and patterns of performance. This involves taking simple measurements of physical and
However, circadian rhythms should not be confused with the discredited biorhythm concept, which was popularized in the s. Involving an unsubstantiated -day physical cycle, a -day emotional cycle, and a -day emotional cycle, this concept resulted in books, charts, and calculators that predict favorable and unfavorable days in one’s life. This discredited concept states that biorhythms are established at birth, do not change, and are identical for all persons with the same birth date. In contrast, scientific studies have shown that true circadian rhythms may be altered by a variety of factors and vary greatly among individuals.-