In 2018, a 69-year-old Dutch businessman began a legal battle to try to change his age: he wanted to get 20 years off his shoulders by claiming that, according to his doctors, he had the body of a 49-year-old man. Our chronological age—the years we have lived—can differ from biological, which measures the degree of aging of cells, tissues and organs. As life expectancy grows, multiple researchers are exploring the potential of epigenetic clocks to understand aging and prevent disease.
To explain the differences between chronological and biological age, Matt Kaeberlein, researcher of the biological mechanisms of aging at the University of Washington (USA), suggests considering the difference between dogs and humans. Chronologically, the aging of dogs is the same as that of humans. That is, a dog that has lived 10 years is 10 years old, as is a child that has lived the same period of time. But, as the expert indicates, a dog that has lived a decade is biologically about 70 years old. “One human year equals seven dog years,” he adds. Or what is the same, dogs age biologically about seven times faster than people.
Age is a risk factor for multiple chronic diseases. In theory, having a lower or higher biological age can mean being less or more likely to suffer from some pathologies of old age, according to Kaeberlein. For example, the expert points out that the risk of having Alzheimer’s disease multiplies by 10 every 15 years of biological age: “A 70-year-old person with a biological age of 55 would be 100 times less likely to develop Alzheimer’s disease than a 70-year-old person with a biological age of 85″.
Calculate biological age
Biological age is the general state of your body compared to the average state of individuals within a population at a given age. Tamir Chandra, expert in the biology of aging at the University of Edinburgh (Scotland). There are different ways to calculate it, but all have their limitations. Christopher Bella human epigenomics researcher at Queen Mary University of London, explains that currently “there is no gold standard to measure biological age and it may not even be possible to do so, mainly because it is a mixed bag for a large number of simultaneous aging-related processes.”
Some methods for estimating biological age take into account a given physiological measure that changes with age and compare it to the average within the population. For example, walking speed or lung function. “This is easily interpretable, as you understand exactly what is being measured,” says Chandra. However, it has a drawback: this approach is based on a single parameter that changes with age.
To estimate biological age with greater precision, in the last decade several researchers have developed epigenetic clocks that take into account multiple facets of the aging process. These kinds of predictors measures changes in DNA methylation that occur with age. Methylation, explains Bell, is a process by which a methyl group (a molecule made up of one carbon atom and three hydrogen atoms) is added to some DNA bases, “which can influence the functionality of genes” . The expert adds that the clocks “work by measuring a small number of these methylated sites in the genome that change over time and work well together to estimate age.” A review published in the scientific journal Nature Reviews Genetics indicates that biomarkers of aging based on DNA methylation data have made it possible to make precise estimates of the age of any tissue.
But epigenetic clocks also have limitations. In addition to the fact that it is unclear whether they reliably measure biological age, research is lacking to know for sure what mechanisms drive these changes in methylation and to what extent they are or are not involved in aging, according to a review published in the journal Aging Cell. “What would happen if we prevented these changes from happening? Would we have changed how fast we age or would we just have broken our stopwatch?” asks Bell. In addition, none of these watches has been able to accurately predict life expectancy or future health information at the individual level.
Despite all these limitations, there are several reasons why these watches have attracted a lot of interest. We are living longer and longer, which has led to a global burden of disease in old age, as indicated by a review published in the journal Nature. If in 2019 life expectancy at birth was about 72 years, The United Nations expects that in 2050 it will rise to 77 years. Several researchers point out that the increase in life expectancy in recent decades has not been accompanied by a reduction in chronic diseases.
A key puzzle in biology is to understand why and how we age, and epigenetic clocks pursue an ambitious goal: to find answers and thus achieve a healthier old age. Chandra stresses that these predictors could be useful in finding out whether and to what extent certain behaviors, such as smoking, cause accelerated aging.
They can also be used for better understand the pathophysiology of some diseases related to ageing, such as diabetes, depression, cardiovascular diseases or dementia. Something that, according to Bell, can lead to new preventive or therapeutic pathways, “so that the increase in life expectancy is accompanied by an increase in healthy life expectancy.””.
Some research indicates that anti-aging interventions are needed to reduce the burden of age-related diseases and protect the productivity of the population. Although it is still early to assess the potential of epigenetic clocks for this purpose, Chandra does not rule out that in the future they will play a key role in the discovery of interventions that delay or accelerate aging.
Exclusive content for subscribers
read without limits