Biological and Chronological Age
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Biological vs. Chronological Age
Aging is a complex process characterized by accumulation of damage, an increase in the vulnerability to disease, decline in the reproductive function, in physical and mental abilities. It affects all cells, tissues, and organs in our bodies. Increased chronological age is closely associated with the risk of death and old age disease.
Chronological age means exactly what it sounds like -- how many years a person was born.
However, aging happens in different people at different rates, and therefore chronological age is not the best indicator of how long a person will live and whether and when that person will experience any old age disease. Many visual signs such as wrinkles or grey hair are not a reliable predictor of a person's state of health and of the expected life span and health span either.
Instead, the term 'biological age' was introduced over 50 years ago to predict susceptibility of a person to morbidities and mortality better than chronological age does. When we are talking about biological age, we are talking about how young (or old) a person is biologically, functionally vs. chronologically.
Chronological age means exactly what it sounds like -- how many years a person was born.
However, aging happens in different people at different rates, and therefore chronological age is not the best indicator of how long a person will live and whether and when that person will experience any old age disease. Many visual signs such as wrinkles or grey hair are not a reliable predictor of a person's state of health and of the expected life span and health span either.
Instead, the term 'biological age' was introduced over 50 years ago to predict susceptibility of a person to morbidities and mortality better than chronological age does. When we are talking about biological age, we are talking about how young (or old) a person is biologically, functionally vs. chronologically.
How biological age is calculated and what it means
Biological Age Definition
Biological age is a concept used to indicate how 'old' a person is compared to a population cohort and the average life expectancy in that population cohort (Jackson, 2003).
Biological age and biomarkers of aging are two concepts that are used together.
To calculate someone's biological age, scientists use a combination of biomarkers and mathematical modeling (Jia, 2017). In part, that mathematical modeling is based on the fact that a biomarker of aging typically closely correlates with chronological age, it changes as a person ages. Many biomarkers decline roughly linearly with age with a slope of <1% per annum (Jackson, 2003).
Scientists test biomarkers (e.g. DNA methylation or telomere length in samples of blood or saliva) in a large and diverse group of population. Test result values of those biomarkers are recorded. Those values can be plotted on a graph. Statistical analysys is used to establish a trend. Test results of most people will fall where the majority of the test results for their age fall. Yet some will fall above or below.
If test results of a 40 year old come back with the same value as test results of an average 36 year old in the tested cohort, then we are saying that the biological age of that person is 36 years.
Biological age is a concept used to indicate how 'old' a person is compared to a population cohort and the average life expectancy in that population cohort (Jackson, 2003).
Biological age and biomarkers of aging are two concepts that are used together.
To calculate someone's biological age, scientists use a combination of biomarkers and mathematical modeling (Jia, 2017). In part, that mathematical modeling is based on the fact that a biomarker of aging typically closely correlates with chronological age, it changes as a person ages. Many biomarkers decline roughly linearly with age with a slope of <1% per annum (Jackson, 2003).
Scientists test biomarkers (e.g. DNA methylation or telomere length in samples of blood or saliva) in a large and diverse group of population. Test result values of those biomarkers are recorded. Those values can be plotted on a graph. Statistical analysys is used to establish a trend. Test results of most people will fall where the majority of the test results for their age fall. Yet some will fall above or below.
If test results of a 40 year old come back with the same value as test results of an average 36 year old in the tested cohort, then we are saying that the biological age of that person is 36 years.
An example of biological age calculation based on DNA Methylation
Biological age based on the DNA Methylation.
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This graph shows real test results from over 650 people, newborns to 100 years old, collected for a scientific study that has not been published yet. The graph is an example of a mathematical model of the biological age based on the DNA methylation.
DNA Methylation values are plotted on the graph; each result is shown as a small black dot. You can see that the distribution is very consistent - on average, the higher the age, the higher the value. The straight rising line shows the trend. |
Two test results (black data points on the graph) are highlighted here, in blue and in red, to explain the biological age.
Both individuals are 45 years old; that is their chronological age. However, -
What is the practical meaning of this? The 45 year old with the biological age of a 32 year old likely has the health and energy levels similar to an average 32 year old. That person is also likely to live longer than other people his/her age.
Even though biological age shows a trend in a person's health and life expectancy, it cannot be used to predict precisely how long the person will live.
Both individuals are 45 years old; that is their chronological age. However, -
- DNA methylation levels of one person are at the levels of a 32 year old (marked with blue circle and blue dotted lines);
- The other person's methylation levels are at the levels of a 65 year old (marked in red).
What is the practical meaning of this? The 45 year old with the biological age of a 32 year old likely has the health and energy levels similar to an average 32 year old. That person is also likely to live longer than other people his/her age.
Even though biological age shows a trend in a person's health and life expectancy, it cannot be used to predict precisely how long the person will live.
Factors that impact biological age and longevity
Some people age better merely due to their genetics. However, only about 25% of the variations in the human longevity are due to genetics. The other 75% are due to lifestyle and environmental factors (Passarino, 2016).
An Anecdotal Tale of lifestyle Influences on Longevity
Let's look at two historic examples of genes vs. lifestyle.
An Anecdotal Tale of lifestyle Influences on Longevity
Let's look at two historic examples of genes vs. lifestyle.
Hildegarde Von Bingen. Lived to be 81 (1098 - 1179).
Henry the VIII. Lived to be 55 (1491 - 1657).
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Hildegard Von Bingen
Lived to be 81 (1098 - 1179). Germany. Abbess/Nun. Sickly from birth. Composer, philosopher, scientist, polymath. Spiritual lifestyle; physically active - gardening, walking; modest diet; intellectual work. Henry the VIII Lived to be 55 (1491 - 1547). England. King. Robust health in the youth. Sedentary lifestyle. Heavy alcohol consumption. Stress and worries. 5000 calories a day diet with minimal raw fruits or vegetables. Lifelong turmoil in the personal and family life. |
Known lifestyle and environment factors that influence our health and longevity (see Baltimore Longitudinal Study or Aging and Blue Zones)
Genetics dictate 25%; the other 75% are at our discretion. By choosing a mindset and environment and following proper lifestyle we can impact how long we will live and how healthy we will be.
- Sleep and circadian rhythm;
- Nutrition;
- Exposure to toxic substances in the air, food, household;
- Physical activity;
- Mental/cognitive activity;
- Sun exposure (also linked to circadian rhythms);
- Stress levels and reaction to chronic stress;
- Social surrounding - friends and family;
- Mindset and spirituality.
Genetics dictate 25%; the other 75% are at our discretion. By choosing a mindset and environment and following proper lifestyle we can impact how long we will live and how healthy we will be.
References and Literature
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