What are the differences between chronological age and biological age?

Chronological age and Biological age are different references when studying aging.

Time is a physical magnitude with which human beings measure the duration or separation between events. This dimension helps us to order events in sequences, establishing a past, a future and a third set of events that are not directly related to these terms.

When we say that "time passes for everyone," we are referring, even if we do not know it, to an essential condition for defining life. Organic matter degrades over time, and this event is essential to conceive of existence itself. Without going any further, there are few more accurate definitions of life, at the biological level, than "the interval between birth and death".

Thus, senescence and demise are an integral part of living organisms. We are born, we grow, we reproduce and we die, in a hitherto infinite cycle of organic matter and energy. Even so, it is curious to know that, although time passes for everyone, it does not do so in the same way according to certain conditions of the organism. Here we present to you the differences between chronological age and biological age.Join us in this world of science and metaphysics.

What is the difference between biological and chronological age?

The chronological age is the one that is marked by the date of birth of the individual.. It is a rather meaningless figure at a biological level, but it is used in the social environment to legislate and categorize population groups based on their knowledge, work aptitude and many other things.

The number of years that defines us is nothing more than a social construct, since a sick person at the age of 30 can have the health and vital prognosis of a 90-year-old individual.

Chronological age is really a chronometric figure, that is, it is only quantified on the basis of the rhythm of a clock.. Although it is a relative and purely mechanical measure, it can be married in a certain way to the biological passage of time.

If on one side of the "equation" you put a clock and on the other a particular physiological process (such as the first ovulation in the female of a given species), a kind of useful bijection is formed.

The distance between birth and first ovulation has been defined chronologically (or rather chronometrically), since a total of X seconds, minutes, days, months and years have passed until reaching that exact point, right? Yes and no. Hang on, for it's time to digress and abstract from typical terms.

While the chronological age is the one that marks the clock and the date of birth of the individual, the biological age is the one that represents his or her internal functional state, marked by the aging of cells, cells, organs, and tissues.marked by the aging of cells, tissues and organs. The difference in the example given above is that physiological processes do not correspond to a physical process that is invariably successive (as is the passage of time on a chronometric level).

Thus, the vital phases of a living being are not determined on the basis of their chronometric distance (year 1, year 2, year 3, etc.), but by the qualities of the physical system in which they manifest themselves. In other words, what conditions the ovulation of a female of a given species is not the time spent, but the concentrations of sex hormones in the blood, for example. We know that all this may sound complex, but it is enough for us to make the following message clear: the biological clock and the mechanical clock do not follow the same temporal patterns..

How is the biological age of an organism determined?

So, what use is the physical time scale to quantify the age of a living being? Undoubtedly, the calendar can give us several clues as to the health of an organism, since generally someone who has spent 20 laps around the Sun on Earth will have statistically more years ahead of him than someone who has lived 80. We stress the term "statistically", i.e., on average, because the cases of early mortality due to pathologies and accidents are there and are an undeniable reality.

For further complexity and interest, it is essential to emphasize that the chronological age and the biological age are distanced on the basis of different parameters. Among them, we have the following:

• Epigenetics: modifications of gene expression that do not respond to a change in the organism's DNA. The genome is "fixed" throughout life, but its expression is not.
• Lifestyle: to confirm this parameter, we need only look at the lung tissue of a chronic smoker and that of a non-tobacco user of the same age.
• Diseases: various diseases can cause cell destruction, which sometimes cannot be recovered. This clearly leads to premature aging.
• Environment: growing up near an industrial plant that emits smoke continuously is not the same as living in the countryside. The body senses environmental variations.

There are several biomarkers that show the discrepancies between biological and chronological age. One of the most widely used biomarkers in this field is the telomeric shortening rate, as you will see below.as you will see below.

Telomere shortening rate and biological age

Telomeres are the ends of chromosomes. They are non-coding (not used for protein synthesis) and highly repetitive (repeating nucleotide sequences) regions of DNA whose function is to give structural stability to the chromosomes of eukaryotic cells.

Telomeres are one of the most interesting bases of aging. Although we do not want to go into complex genetic terms, it is enough to know that, with the duplication of genetic information, it is impossible to transcribe absolutely all the DNA. Thus, as a cell line divides and renews as a cell line divides and renews itself, the telomeres become shorter and shorter.. When they reach a critical length, aging processes are triggered, as the integrity of the cell itself is destabilized.

It is even more interesting to know that there is an enzyme called telomerase present in germline cells, which is found in fetal tissues and is capable of causing telomere lengthening. Telomerase is repressed in mature somatic cells after birth, resulting in telomere shortening after each cell division in adult tissues.

Deficiency in telomerase levels at key developmental stages results in the early onset of pathologies such as aplastic anemia, immune problems or pulmonary fibrosis, in other words, accelerated aging and increased biological age.The deficiency in telomerase levels at key developmental stages results in the early onset of pathologies, such as aplastic anemia, immune problems or pulmonary fibrosis, in other words, accelerated aging and an increase in biological age. Thus, it is deduced that the rate of telomeric shortening (and the previous action of telomerase) are perfect biomarkers to predict the biological age of the individual, regardless of what a clock or calendar shows.

Every part of our body has an age

Surprising as it may seem (and saving terminological distances), your brain can be "younger" than your left leg, for example.. Imagine comparing the "age" of an alcoholic's liver with that of, say, his eyes.

Chronic alcoholism can lead to cirrhosis of the liver. When exposed to toxic agents over time, the hepatocytes (main liver cells) are destroyed, and this space is replaced by scar tissue. This new tissue does not have a purifying function and so, little by little, the liver loses its capacity. One could say from an abstract point of view that the liver has aged at a dizzying rate.

The same person can maintain adequate eye health and not have suffered any refractive error or eye pathology throughout his or her life. While his ocular apparatus remains young, his liver is that of an elderly person. As you will understand, there comes a point at which the two events coincide, as chronic failure of a vital organ often leads to a general systemic collapse.

Summary

Fascinating, isn't it? Time is still a social construct and, as such, does not define the totality of what surrounds us. The physiological stages of our organism are part of a widely interconnected internal system, so they do not have to be governed by the hands of a clock in all cases.The physiological stages of our organism are part of a largely interconnected internal system, so they do not have to be governed by the hands of a clock in all cases.

Genotype, heredity, family history, lifestyle, environmental conditions and many other factors shape the concept of biological age. Thus, although time passes for everyone, we can assure you that it does not do so in the same way for each individual.

Bibliographic references:

• Cirrhosis of the liver, Clínica Universidad de Navarra (CUN). Retrieved February 23 at https://www.cun.es/enfermedades-tratamientos/enfermedades/cirrosis-hepatica.
• Biological age, Genotypy.com. Retrieved February 23 from https://genotipia.com/edad-biologica/
• Rodríguez López, A. (2019). Literature review: common methods for biological age estimation.
• Toro, J. M. (1997). Old age and aging from the perspective of experimental behavioral synthesis. Revista Latinoamericana de Psicología, 29(3), 459-473.
• Vargas, E., & Espinoza, R. (2013). Time and biological age. Arbor, 189(760), 022.