Science Behind Index

What Is Your Biological Age? And Why Does It Matter?

How fast have you been aging? Let us explain.

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If you haven’t yet heard, you have two ages. Surprise! The one you know already is that number tracking the times you’ve travelled around the sun or the one on your driver’s license — your chronological age. The other, which you may not be aware of, is tracking the way your cells have changed as you’ve been alive — your biological age. A quick entry in a Pearson Chronological Age calculator and you can figure out your chronological age to the day. On your birthday, people could shout, “Happy Chronological Age Day!” — although it doesn’t work so well with cake and candles. 

Your cells, rudely enough, do not celebrate your birthday. With only some regard for your chronological age, your tissues, organs and blood reflect your “phenotypic age,” more commonly known as your biological age. Biological age is a measurement of your age based on various biomarkers — a number that can change due to lifestyle and other health factors. 

“Knowing your biological age is an effective way of determining your cumulative rate of aging,” says Morgan Levine, Ph.D., assistant professor of Pathology at the Yale School of Medicine and Elysium’s Head of Bioinformatics. Cumulative rate of aging is your biological age relative to your chronological age — a measure of the pace at which your body has aged for every year you’ve been alive. Your biological age reflects a combination of your genetics, accumulated lifestyle factors, and other determinants such as demographics, diet, and exercise habits.

Life’s not predictable enough for us all to see a 1:1 match in chronological age and biological age. So as we pass the days and months and years, our cells either progress more or less rapidly than what is expected from our chronological age. After knowing your biological age, you can choose to adapt lifestyle changes that may improve your overall health.

The Epigenome’s Connection to Biological Age

Your genome is your complete DNA (deoxyribonucleic acid), which holds the instructions for building the proteins that carry out a variety of functions in a cell. Your epigenome is made up of chemical compounds and proteins that can attach to your DNA. They tell the DNA what to do — turn on and off, make this protein or that. When epigenetic compounds attach to DNA, they are said to have "marked" the genome. These marks do not change the sequence of the DNA, but they do change the way cells read the DNA's instructions. DNA methylation is one type of mark, and it can be identified and tracked as a sign of aging in different parts of the genome.

To simplify, Levine makes the analogy of a kitchen pantry stocked with ingredients and a cookbook. “Your genes are all the ingredients and epigenetics is the cookbook,” she says. “You might not use all the ingredients, and the instructions will determine which you’ll use and those you won’t.” 

If your body needs to create new fingernail cells, it’ll look at the section of your DNA for fingernails and read only that part and use a specific set of ingredients to begin production of new fingernails. Your genome (the ingredients) always stay the same, but the epigenome (the recipes) changes over a lifespan. A little more salt here, a dash more tumeric there. As it changes, it marks the genome via DNA methylation. To calculate biological age, scientists like Levine take a sample of cells and look at specific sites along the genome and see what proportion of the cells are marked with DNA methylation.

“In certain areas of our genome the methylation changes very precisely with age,” Levine says. Some regions see an increase in methylation with age, other regions see a decrease. If, for example, 60% of cells from a sample show DNA methylation at one site of the genome, scientists can match that percentage with a specific chronological or biological age. Horvath’s study used 353 sites on the genome to predict chronological age — comparing the data to existing data on chronological age. Levine’s work uses thousands of sites to predict biological age — comparing the data to biomarker signatures of biological age. Some sites are more accurate than others, so the cumulative age is a weighted average of all the sites.

Despite the neatness — and usefulness — of one biological age number, in reality, your tissues and organs all have their own biological age. “It’s your personalized mosaic,” Levine says. “It’s a combination of biological ages that reflect the age at which your body is expected to function .” At this stage, the averaged biological age is one of the best biomarkers for predicting a variety of aging outcomes. In the future, the goal is to become more and more specific with biological age in different parts of the body.

How to Understand Your Biological Age

Knowing your biological age is a big step in understanding the entirety of your health profile. But the second aspect is equally important: tracking your biological age. Because biological age can shift, seeing changes over time is vital to understanding what is good and bad for your health. 

“Different behaviors will affect different biological ages in a different way,” Levine says. “The only way to know what is working for you is to have an outcome measure that’s tracking how the different things you’re doing in your life are actually influencing your health.”

There is no single factor, and no guarantee that healthy living will improve your biological age or change the rate at which your biological age will change. Nonetheless, there are a number of things you can do to improve overall health and thereby increase the likelihood of slowing biological aging: diet, cultivating healthy relationships, managing stress, sleep, and exercise. Seeing a steady decline in biological age as you chronologically age is the goal, and as you age, variance increases. At 16, your biological age is likely to be close to chronological. But at 60, there’s a wider spread. 

Keep in mind that you should not rely on your biological test results to screen, diagnose, treat, cure, or prevent any disease or condition or assess risk of any disease or condition, unless indicated otherwise by the test. Also, unless advised by your healthcare professional, biological age should not be used to determine or alter any chronological age-related health or medical treatments.

With scientific advances, a simple spit sample can be a reliable biomarker for your biological age, making it much easier to determine and track your health. Knowing where you stand and the habits that can affect your biological age can be a key component, together with healthy living, of improving your overall health. Ideally, like your chronological age, your biological age will be a number worth celebrating.

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