Do you ever wake up and think, “When I was younger, I could get by on just four hours of sleep, but now it feels like I need 10”? Or have you ever walked out of the gym and “felt” your knees?
Nearly everyone experiences these signs of aging. But there are those who seem to defy their years. The late Supreme Court Justice Ruth Bader Ginsberg remained on the bench until her death at 87. “Great British Bake Off” judge Mary Berry, now in her 80s, continues to inspire people around the world to bake and enjoy life. And actor Paul Rudd was named People magazine’s “Sexiest Man Alive” in 2021 at the age of 52, despite still looking like he’s in his 30s. So is age just a number?
Researchers have devoted much attention to understanding the causes and risk factors of age-related diseases such as Alzheimer’s, dementia, osteoporosis and cancer. But many ignore the single most important risk factor for all of these diseases: aging itself. More than any individual risk factor, such as smoking or lack of exercise, the number of years you live predicts the onset of disease. In fact, aging increases the risk of several chronic diseases by up to a thousand times.
However, no two people age in the same way. Although age is the leading risk factor for several chronic diseases, it is an unreliable indicator of how quickly your body is deteriorating or how susceptible you are to age-related diseases. This is because there is a difference between your chronological age, or the number of years you have lived, and your biological age – your physical and functional capacity.
I am a scientist interested in redefining “age.” Instead of benchmarking chronological age, my lab is invested in measuring biological age. Biological age is a more accurate measure of health span, or years lived in good health, than chronological age, and does not directly correlate with wrinkles and gray hair. People who age rapidly experience a faster rate of functional decline relative to their chronological age.
My grandmother, who lived to be 83 but was bedridden and had no memory of who I was for the last few years of her life, was a quick parent. My grandfather, on the other hand, also lived to be 83 but was active, functional, and even did my homework with me until he passed away – he was a healthy parent.
With the unprecedented growth of the world’s aging population, I believe that finding ways to measure biological age and how to maintain or slow its progression is not only critical to the health of the individual, but also to the social, political, and economic health of our society. Detecting rapid aging early offers an opportunity to slow, change, or even reverse the trajectory of biological aging.
Genetics and biological age
Biological aging is multifaceted. It arises from a complex mix of genetic traits and is influenced by factors such as microbiome composition, environment, lifestyle, stress, diet and exercise.
Genetics were once thought to have no influence on aging or lifespan. In the early 1990s, however, researchers reported the first studies identifying genes that could extend the lifespan of a small roundworm. Since then, multiple observations have supported the influence of genetics on aging.
For example, children of long-lived parents and even children with long-lived siblings live longer. Researchers have also identified multiple genes that influence longevity and play a role in resilience and protection from stress. These include genes that repair DNA, protect cells from free radicals and regulate fat levels.
However, studies of identical twins – who share the same genes but do not have the exact same lifespan – clearly show that genes are not the only factor influencing aging. In fact, genes probably account for only 20% to 30% of biological age. This suggests that other parameters can strongly influence biological aging.
Environmental and lifestyle impacts
Researchers have found that environmental and lifestyle factors have a major influence on biological age, including social connectedness, sleep habits, water consumption, exercise, and diet.
Social connectedness is essential for well-being throughout life. However, social connections can be difficult to maintain due to loss of family and friends, depression, chronic illness, or other factors. Several studies have reported a strong association between social isolation and increased stress, morbidity, and mortality.
Likewise, diet and exercise are powerful influencers of biological age. Blue zones, areas around the world where people live long, attribute their successful aging to diet, exercise, and social connection. Mostly plant-based meals and bursts of activity throughout the day are known “secrets” to health and longevity. Although newer studies on the effects of dietary interventions like intermittent fasting and time-restricted feeding on longevity have not been rigorously tested, they do show multiple health benefits, including better glucose and insulin regulation.
Although genetics are difficult to control, diet and exercise can be modified to slow biological aging.
How to Measure Biological Age
Currently, there is no effective test to predict an individual’s health development early enough in life to intervene and improve quality of life with age. Scientists are interested in identifying a molecule that is sensitive and specific enough to serve as a unique fingerprint for biological age.
It is important to consider the health and resilience of the individual when discussing biological age rather than focusing solely on disease state. Resilience is the state of adapting and recovering from a health problem and is often more predictive of functional health. A molecular aging fingerprint can be a tool to identify people who are less resilient and need more aggressive monitoring and early intervention to maintain their health and help reduce gender, racial, and ethnic health disparities.
There are several promising molecular markers that can serve as biological age identifiers.
One of these markers is epigenetic clocks. Epigenetics are chemical modifications of DNA that control gene function. Several scientists have discovered that DNA can be “marked” by methyl groups in a pattern that changes with age and could potentially serve as a readout for aging.
It is important to note, however, that while epigenetic clocks have been valuable in predicting chronological age, they do not equate to biological age. Furthermore, it is unclear how these epigenetic marks work or how they contribute to aging.
Another well-known marker of biological age is the buildup of dysfunctional cells, called senescent or zombie cells. Cells become senescent when they experience multiple stresses and become so damaged that they can no longer divide, releasing molecules that cause chronic low-grade inflammation and disease.
Animal studies have shown that removing these cells can improve health. However, what exactly defines senescent cells in humans is still unknown, making them difficult to track as a measure of biological age.
Finally, the body releases unique metabolites, or chemical fingerprints, as byproducts of normal metabolism. These metabolites play a dynamic and direct role in physiological regulation and can inform functional health. My lab and others are working to determine the exact composition of these chemicals to figure out which ones best measure biological age. Much work remains to be done, not only to identify these metabolites, but also to understand how they influence biological age.
People have long sought a fountain of youth. Whether such an elixir exists is still unknown. But research is beginning to show that delaying biological age may be a way to live healthier, fuller lives.
This article is republished from The Conversation, a nonprofit, independent news organization that brings you facts and reliable analysis to help you understand our complex world. It was written by: Aditi Gurkar, University of Pittsburgh
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Aditi Gurkar receives funding from the National Institute on Health, the Richard King Mellon Foundation, and AFAR/Hevolution.