In The Curious Case of Benjamin Button, the titular character (played by Brad Pitt) lives a life in reverse. He’s born an old man and grows younger as he ages, eventually dying a newborn infant. The film explores the constant shift of identity through the passage of time, but it also unexpectedly mirrors a scientific reality: Parts of our bodies aren’t all aging at the same pace.
According to a study published Wednesday in the journal Nature, some of your organs are aging faster than others. Examining blood samples from over 5,600 adults, the researchers used machine learning to identify proteins produced by specific organs that are associated with aging. They estimate that nearly 20 percent of the population — or one in five healthy adults — has at least one organ aging at a fast clip, which may increase a person’s risk of death or it may suggest disease is brewing in that organ. While aging is inevitable, this finding may pave the way for a simple blood test to catch the first wrinklings and prevent disease before it strikes.
Organ age gap
There have been a lot of studies on mice that looked into how aging happens at the molecular level in different organs. These studies found that each organ ages in its own unique way and at its own pace. Also, depending on the organ — like the brain, heart, or kidneys — there's a big difference in how likely they are to develop age-related diseases.
Whether this rings true for human organs at the molecular level is still an area of active research. Scientists have come up with different ways of measuring biomarkers corresponding to age. However, most of these methods look at an “individuals’ biological age — the age implied by a sophisticated array of biomarkers — as opposed to their chronical age, the actual numbers of years that have passed since their birth,” Tony Wyss-Coray, a professor of neurology at Stanford University and the study’s lead researcher, said in a press release. Additionally, methods that do look at specific organs only tell us how well they function, not so much specific details on aging.
In the new study, Wyss-Coray and his colleagues examined age-related changes in proteins produced by 11 different organ systems or tissues among 5,678 participants of adults. These organ systems or tissues include the heart, fat, lung, immune system, kidney, liver, muscle, pancreas, brain, blood vessels (or vasculature), and the intestine.
Using machine learning, the researchers identified around 858 abnormal organ-specific proteins, from among 5,000 proteins in an average blood sample, that appeared to be correlated with susceptibility to disease and accelerated biological aging. They then determined the mortality or disease risk associated with an “age gap,” or the difference between an organ’s chronological age and its estimated biological age based on the proteins produced.
“When we compared each of these organs’ biological age for each individual with its counterparts among a large group of people without obvious severe diseases, we found that 18.4 percent of those age 50 or older had at least one organ aging significantly more rapidly than the average,” Wyss-Coray said. “And we found that these individuals are at heightened risk for disease in that particular organ in the next 15 years.”
For organs like the heart, otherwise healthy individuals with accelerated aging were 2.5 times at a greater risk of heart failure compared to people with normally aging hearts. For the brain, individuals with aged brains were 1.8 times more likely to show cognitive decline over five years compared to folks with more youthful brains. Aging in organs like the kidney was strongly associated with both hypertension and diabetes.
An aging test on the horizon?
While it can be disheartening to learn your ticker might be aging faster than your liver, a singular hope from these findings is the potential for a screening test sniffing out or monitoring the pace at which an organ ages.
However, this will require much further research, especially as this study has some limitations. For instance, the majority of the participants were Caucasian. This raises the question of whether the findings would be the same for people from different ethnic backgrounds or different parts of the world. The researchers also didn’t look at all organs, like the reproductive system, which the researchers say they did to avoid making conclusions about organs they didn't have enough convincing data about how those organs age.
This research also raises the importance of better understanding genes winding organ aging “clocks” and how these genes may differ within a population.
“If we can reproduce this finding in 50,000 or 100,000 individuals,” said Wyss-Coray, “it will mean that by monitoring the health of individual organs in apparently healthy people, we might be able to find organs that are undergoing accelerated aging in people’s bodies, and we might be able to treat people before they get sick.”