- 1 Hypothalamus and Time-keeping Genes
- 2 Larks and Owls
- 3 Mood and Exercises
- 4 Disease symptoms vary with Circadian rhythms
- 5 The relativity of Diagnostic Results
- 6 Circadian rhythm Disorders
- 7 Chinese Chronobiology
- 8 Macrocosm and Microcosm
- 9 Circadian rhythm Biological Mechanisms discoveries earns Scientists the 2017 Nobel Prize of Physiology
The study of circadian cycles in the body is called chronobiology. When i studied Chinese Medicine, this subject was an important part of the three years training. In effect, the flow of time impacts not only human behavior, but also human diseases.
Most of the physiologic activities in the body are not constant throughout the day, but show variations. Some functions are more active in the first hours of the day while for others, the activity is more pronounced in late hours. This diurnal variation of activities is called “circadian cycle” or “circadian rhythm”. “Circadian” literally means “around the day”. Circadian rhythms cause changes in our physiological, mental and behavioral patterns that follow a roughly 24 hour cycle.
Almost all functions follow this rhythmicity. Our sleep-wake cycle, the thermoregulation, or regulating the body temperature, secretion of many hormones and body immunity all show circadian rhythm. Hematocrit, red blood cell and hemoglobin show significant change with time of day. Total cholesterol, HDL-cholesterol, beta-lipoprotein, triglyceride and blood glucose also reveal alterations with time of day. Parasympathetic system is more active in the night while sympathetic activity is usually more noticeable in the day. Cortisol level is highest in the morning and lowest in the evening. The same pattern also exists for melatonin, the pineal gland hormone. There is also a diurnal change in blood fluidity. Our lung functions are different in day and night. Growth hormone release also shows daily change. There is almost no physiologic activity that is spared by the rhythmicity.
Hypothalamus and Time-keeping Genes
It is generally believed that there are “biologic clocks” within our body that control these rhythms. These biologic clocks are groups of cells throughout the body and are controlled by a “master clock” in hypothalamus, which is a complex of nerve called Suprachaismatic nuclei or SCN. The SCN is actually two clusters of 50,000 neurons, and works with several genes.
Together, the SCN and these timekeeping genes make up the central clock which governs many aspects of physiology and behavior. They orchestrate the daily rhythms and cycles that control the ebb and flow of hormones, chemicals and neurotransmitters and these chemicals determine wake, sleep, appetite, sex and other key aspects of our lives.
Apart from the genetic aspect, the circadian rhythm is also under significant influence of some environmental factors, the most important being light. There is neural link between the retina and the SCN which conveys to it the day and night signals. Light may also affect switching on or off the genes that direct circadian rhythm.
Circadian rhythm “clocks” , other than the “master clock” are dispersed in many organs and cells in the body outside the suprachiasmatic nuclei (SCN).These “clocks”, also called peripheral oscillators, are found in the esophagus, lung, liver, pancreas, spleen, thymus
We know that we may perform differently for varied types of activity in different times of the day. Runners, cyclists and swimmers perform better in the afternoon, when body temperature and aerobic activity is in the peak. Fencers, on the other hand show better actions in the middle of the day, since at this time there is better concentration and mental activity.
Larks and Owls
There are also individual differences among people in their circadian cycles. Some people, usually called, “larks” sleep early and rise early. Others, the “owls”, burn the midnight oil and get up late the next morning. While “larks” are at their best late in the morning and early in the afternoon, “owl” seem to be warming up just around the noon. Their most pleasant time is usually after 6 in the evening. The difference between “larks” and “owls” is usually a matter of genetics. Teen agers are usually very difficult to get up in the morning. They are scorned by the parents for such laziness, but now we know that many times, it is not a matter of laziness, but adolescent development passes an “owl-like” stage.
Mood and Exercises
The Best mood for larks is between 9am and 4pm and for Owls is between 3pm and 10pm. larks are most reproductive between 9am and 1pm while for owls this time is between 7pm and 12am
The Best time to exercise for larks is between 4pm and 6pm and for Night Owl between 5:30pm and 7:30pm. The highest mental performance for larks is between 8am and 10am and for Owls is between 7pm and 9pm
Disease symptoms vary with Circadian rhythms
Like the physiologic activities which change during a day, disease symptoms may also show the same diurnal variation. Fevers are usually worst in the evening. Allergic rhinitis with 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, is aggravated in the few hours prior to awakening than during the day.
Angina pectoris, with chest pain and electrocardiographic (ECG, EKG) abnormalities are most common during the first 4 to 6 hours after awakening. Heart attacks are seen commonly in the early waking hours. 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. Symptoms of rheumatoid arthritis are most intense upon awakening. Osteoarthritis: Symptoms of osteoarthritis worsen in the afternoon and evening.
The relativity of Diagnostic Results
Circadian cycles can also affect diagnostic test results. These results can vary significantly, possibly producing inaccurate readings, depending on the time of day when a test is done. For example, 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. 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. Furthermore, many elements in blood like iron, many hormones, phosphorus and so many others do not have the same concentration in the morning and in the afternoon.
Circadian rhythm Disorders
Disorders of circadian rhythm may be seen. Shift workers are quite prone to developing circadian rhythm disorders. These disorders can be categorized as acute and chronic. The acute ones are usually transient. The most common acute type is “jet lag” or more scientifically termed “Rapid Time Zone Change Syndrome. This happens when traverse long distances in a short time. The symptoms include sleeplessness, fatigue and decrease of daytime alertness, to which can be added high blood sugar and stress hormones.
The chronic forms are usually more complicated. These include: delayed sleep-phase syndrome (DSPS), advanced sleep-phase syndrome (ASPS), and irregular sleep-wake cycle, seasonal affective disorder (SAD).
It is known that workers who work all night have more cancer and Alzheimers. Which makes sense because melatonin is one of the strongest antioxidants that fights cancer cells while the body’s repair mechanisms and brain detox system get activated at night.
In chinese medicine Chi energy has a cycle during the 24 hours. For two hours , each organ network (that is organ with its associated meridians) has the maximum flow of Chi and therefore shows maximum activity. Thus, energetic flow in different parts of the body has a diurnal rhythm. Ancient chinese and classical chinese medicine practitioners believed that the more our daily life is consistent with this cycle the healthier we are. This is also an important element in Taoism, where Nature has a dominant role.
Top: a chart showing correlations of the modern view of circadian rhythm with that of the ancient chinese one
Many ancient philosophies used to think of human beings as small models of universe. They had the idea that whatever happens in the universe has an equivalent in the body. This is why they called the universe the macrocosm and the human beings the microcosm. They believed that the main secret to health and longevity was living in accordance with nature.
In the same way, one of the fundamental principles that structures Happiness and Holistic Medicine is based on respecting the billion years old microbiota (intestinal bacteria), Nature and all of their circadian rhythms. It is a small price for added Happiness, Health and Longevity.