If we revealed the answer to the question in the first line, we would be doing spoilersso let’s get to know the plot of this story a little better.
The word biorhythm simply means biological rhythm, so, in principle, it is a very correct term. However, it is a word that we chronobiologists try not to use.
The reason is very simple: consulting Wikipedia, we find that biorhythms claim to predict various aspects of an individual’s life using simple mathematical cycles. These cycles are supposed to depend on the moment of birth and follow sinusoidal waves with a period of 23 days for the physical aspect, 28 for the emotional and 33 for the intellectual. This pseudoscientific belief became popular in the 1970s.
Given its “resemblance” to the Chronobiology, which focuses on the study of biological rhythms, the terms tended to be confused. Moreover, in many cases Chronobiology was appealed to validate the “biorhythmic”. But the truth is that biorhythmics has no scientific basis and is considered a pseudoscience that, in some way, has contaminated the social perception of Chronobiology.
But they have nothing to do. Chronobiology is an exciting (and rigorous) scientific discipline that explains the seasonal rhythms of reproduction of species, the existence of nocturnal and diurnal animals, why fever rises in the afternoon, why it is more likely to suffer a cardiovascular episode in the morning or one of asthma at night, and a host of other things that affect us directly.
life has rhythm
Life has developed in a cyclical environment imposed by the punctual arrival of day and night, as well as the seasons. Anticipating these regular events has allowed organisms to adjust their physiology predictively, to anticipate and prepare “in advance” for reproduction, overnight fasting, migration, etc.
This measurement of time depends on the existence of a biological clock, which in the case of mammals is found in the brain, specifically in an area of the hypothalamus called the suprachiasmatic nucleus. But in addition to this main clock, oscillators exist in virtually every organ and tissue in the body. Together they make up the circadian system.
To this must be added a molecular clock, whose detailed description earned Jeffrey C. Hall, Michael Rosbash and Michael W. Young the 2017 Nobel Prize in Physiology and Medicine. Finally, this award put Chronobiology on the map. Since then, the temporal dimension has been part of the most cutting-edge research in multiple fields. Although it is still not studied in textbooks, as is the case with the cardiovascular, respiratory or digestive systems.
tick tock melatonin
The biological clock transmits a temporary signal to the rest of the body through a hormone, melatonin, whose concentration increases at night in all species, both diurnal and nocturnal.
Thanks to this hormone, the different physiological variables present rhythms with a period close to 24 hours, and therefore circadian, which means close to the day.
Basically, the main clock, the suprachiasmatic nucleus (or better the nuclei, since it is a paired anatomical structure), acts as an orchestra conductor whose baton is melatonin. This baton ensures that each of the instruments of the orchestra, that is, our physiological variables, enter at the appropriate time to create the melody that maintains the temporal order of our body and, with it, our health and well-being.
As a curiosity, melatonin is a chronobiotic, which means that it adjusts the time that our clock shows and prepares us for the night. That is why the body temperature of a nocturnal animal increases while that of a diurnal animal decreases.
Rhythms that last more than a day (or less)
Circadian rhythms are not the only biological rhythms out there. Rhythms are actually classified based on the number of complete oscillations that occur in a day. If there is more than one, we will talk about ultradian rhythms (for example, breathing, the feeding rhythms of a newborn or the alternation of sleep phases). And if the cycle lasts more than 24 hours we will talk about infradian rhythms, as in the case of the menstrual cycle.
Although the truth is that it can be a little more complicated, since there are also circannual or seasonal rhythms, circatidal, circalunar (which is also the case of the menstrual cycle) or even circaseptan, depending on whether the rhythm is close to the year, to the tides , to the lunar cycle or to a week, respectively. And be careful, the rhythms have an endogenous character! That means that they would continue to exist even if the environmental factor that readjusts them over time were constant.
But be that as it may, we always talk about biological rhythms and not biorhythms. It is a real pity that a beautiful word so easy to understand has been tarnished by the use that a pseudoscience has made of it.
It is time to claim its place in the scientific discipline to which it belongs in its own right, and let the pseudosciences fade away. The way to achieve it is precisely this, that you, the reader, know a little better what Chronobiology is and what this science can contribute to our daily lives.
María de los Ángeles Rol de Lama receives funding from the Ministry of Science, Innovation and Universities and the State Research Agency (RTI2018-093528-B-I00), of the European Union (Call H2020-sc1-BHC-2018-2020, Grant agreement 825546, Diabfrail-Latam), and the Ministry of Economy and Competitiveness, through the Carlos III Health Institute (CIBERFES, CB16/10/00239), all of them co-financed with FEDER Funds. She is a founding partner of Kronohealth SL (2017), a technology-based company owned by the University of Murcia (spin-off).