Chronobiotics are any substance, including many prescription medications and dietary supplements, that influence and alter the body’s circadian and circannual rhythms (“around the year”). Prescription sedatives, sleeping pills, antidepressants, and stimulants are chronobiotics and all affect the body’s normal circadian rhythm. Coffee is a chronobiotic when used to increase alertness and prevent the onset of sleep. Over-the-counter sleep aids and “alertness” preparations alter the normal functioning of the circadian rhythm, which can lead to even more difficulty in sleeping or staying awake.
This site is primarily about prescription, manufactured chronobiotic medications, not about herbs or stuff like coffee.
Circadian rhythm, meaning “around the day” and also called the biological clock, is an internal clock that is synchronized with the 24.5 hour light/dark cycle and the earth’s rotation. Entrainment is the result of the continual circadian rhythm adjustment that occurs within the human body from environmental time cues, mainly the presence or absence of light. Body temperature, blood pressure and heart rate, hormone secretion, alertness, energy, mood, and weight gain are affected by the body’s circadian rhythm. The circadian rhythm also has an impact upon the effectiveness of certain medications; this is the reason why some medications have instructions as to the specific time they must be taken.
The "clock" part of the brain - the suprachiasmatic nucleus - is rich in cells that have receptors for melatonin. Two biochemical receptors have been identified: MT(1) and MT(2) Melatonin's influence on the sleep/wake rhythm cycle is thought to be due to its action on those receptors. Other organs in the body have clocks, too, incuding the retinas and adrenal glands. The suprachiasmatic nucleus is often called the "master clock" (or pacemaker or oscillator) for the body.
Science's understanding of the circadian timing system has increased greatly in recent years - some refer to it as a "clockwork explosion".
Synthetic melatonin derivatives have been created that can activate those receptors and can increase sleep duration in rats.
The most well-known chronobiotic is the hormone melatonin, which was discovered in 1958. All mammals, including humans, secrete melatonin as a response to changing light levels which in turn regulates internal circadian and circannual rhythms. Darkness cues an increased production of melatonin, while light cues a decreased production of the hormone. The amount of melatonin secreted and the sensitivity of melatonin receptors in the body changes during the day, with the highest sensitivity at dusk and dawn.
Melatonin is especially important for the onset of sleep, but it is also necessary for the proper functioning of our cardiovascular, immune, endocrine, and metabolic systems. Cued by darkness, melatonin levels rise which decrease body temperature, heart rate, blood pressure, pupil size, and alertness; all normal body states during sleep. The presence of light reverses this process, resulting in awakening and alertness.
Melatonin acts as a sedative and chronobiotic; it lowers anxiety, decreases pain, prevents inflammation, and has antioxidant effects. Alterations in normal levels can lead to the development of mood and behavioral disorders, and can also affect body weight. People with severe depression have reduced melatonin levels, an unsynchronized circadian rhythm and severe sleep disturbance.
Melatonin is also secreted by other tissues and organs in the body; this melatonin acts as an antioxidant, scavenging free-radicals and decreasing the risk for the development of cancer. Melatonin also prevents premature death of normal cells while destroying tumor cells. Melatonin is necessary for normal bone health and immune function, and detoxifies potentially harmful chemicals. Melatonin also enhances the action of other drugs or hormones in the body.
Laboratory studies in vitro and in animals and clinical investigation of people has shown melatonin has two functions. It plays a part in maintaining sleep (and in initiating sleep) and it influences the body's 24-hr circadian rhythms. This hard science has led drug companies to investigate molecules that are similar to melatonin for possible use against insomnia. These drugs are called agonists or analogs.
Today’s hectic lifestyle has resulted in a large number of people with altered circadian rhythm sleep disorders. Sleep disorders affect all aspects of life; including school and work performance as well as a person’s mental and emotional health. Working or driving with a sleep debt decreases alertness and response time, which can lead to injury or even death. A large number of people have resorted to either prescription or over-the-counter sleep aids; however, the use of these sleep aids can contribute to their problem by negatively altering the body’s normal circadian rhythm.
Scotobiology has recently (in the 2000s) been coined to identify biological study of darkness on living things. It is not clear how scotobiology is distinct from photobiology.
Read about different types of chronobiotic substances.
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