In 2008, at Inonu University Liver Transplant Institute in Malatya, Turkey, a 19-year-old girl lay desperately in a hospital bed. She was suffering from a dangerous condition called hepatic encephalopathy. This happens when the liver fails so badly it can no longer filter toxins from the blood.
As a result, toxins build up and severely damage the brain. With her condition critical, doctors placed her on the urgent liver transplant waiting list. But all she faced was a hopeless wait.
No suitable liver was available for the 19-year-old girl.
Then one day, doctors noticed her vital signs had dropped to a critical low. Her liver had completely failed, and they needed to save her life immediately. Reluctantly, the transplant coordination center informed the doctors they had an available liver that all other hospitals had rejected.
Indeed, it was a very damaged liver. It contained a cystic tumor caused by a parasite and had belonged to a 93-year-old woman who had just passed away. By transplant standards, this liver was unsuitable, especially for a young 19-year-old.
But it was the girl’s last chance at survival. The doctors went ahead with the transplant, and amazingly, it was a success. Not only did the young woman survive, but she recovered remarkably. Six years after the surgery, she gave birth to a healthy baby.
In 2015, on her child’s first birthday, she also celebrated another special milestone. That day marked the 100th birthday of her transplanted liver.
Every organ in our body has its own age
This story proves that inside our bodies, some organs can live longer than their owners. The liver of that 93-year-old woman could have continued functioning if she had lived.
Conversely, some organs die before the body does. They age faster, weaken, and deteriorate, just like the young girl’s liver at 19.
In many cases, an organ’s age can be a more important measure than your actual age. Scientists call this your “biological age.”
Biological age is estimated using biological markers in the body rather than the number of years you’ve lived. These two numbers don’t always match. Each organ’s age is based on its own biological markers.
A healthy young adult in their 20s or 30s may look youthful, but unhealthy habits can age their pancreas to look like that of a 50-year-old. One study even found a 38-year-old with kidneys aged over 60.
On the flip side, some people over 80 have hearts that seem decades younger. They maintain a strong heart by exercising and taking good care of it.
Geneticist Michael Snyder from Stanford University compares the human body to a car. Over time, all parts wear down. “But among the components, some parts wear out faster than others,” he explains.
Data from organ transplants offers fascinating clues about how different organs age. Some organs can be younger or older than their owner’s actual age.
The heart and pancreas tend to age faster after 40. However, lungs often stay younger if you take care of them and avoid smoking. The cornea is one of the most durable organs, least affected by aging.
At the cellular level, the concept of organ age is even less clear. Scientists know cells that make up organs wear out over time.
Genes contain a self-destruct trigger that causes cells to die after a while, replaced by new cells. This process happens regularly, meaning cells and tissues in every organ regenerate.
But regeneration rates vary widely between cell types and organs. Red blood cells in your arteries and veins live about four months. In contrast, red blood cells in the small intestine are replaced every few days.
At the other extreme, most brain and nerve cells last a lifetime. They aren’t replaced, so their death can cause serious problems.
How do we measure an organ’s age?
Researchers at the University of Liverpool believe the complexity of an organ’s structure and its reliance on blood vessels are key factors in determining its age.
Interestingly, some organs are more sensitive to our lifestyle. Lungs are a prime example, says Richard Siow, director of aging research at King’s College London.
Smokers’ lungs age faster than non-smokers’. Studies also show city dwellers’ lungs age earlier than those of rural residents due to pollution.
According to Siow, any lifestyle factor can influence how our bodies age. What we eat, how we eat, how we sleep, and our sleep schedules all affect our organs differently.
Clearly, not all organs age at the same rate. To live longer and healthier, it helps to know which parts of your body are aging first.
But accurately estimating an organ’s biological age is no simple task. Many websites offer age estimates for the heart or lungs, but most lack scientific backing.
To determine an organ’s age, you need detailed tests of its function, tissue structure, cellular makeup, and even DNA.
A 2020 Stanford University study identified at least 87 molecules and microbes in the body that can serve as biomarkers to estimate human organ age. Tracking volunteers quarterly over two years, researchers found these biomarkers reflect aging through different biological mechanisms.
They also discovered people could be grouped by dominant aging patterns in organs or systems, such as kidneys, liver, metabolism, or immune system.
Just like someone with high cholesterol needs heart health checks and exercise, a person with a high liver aging index might need to cut back on alcohol and sugary drinks.
These biomarkers could one day help determine each organ’s age, guiding personalized health advice from a young age.
Recent advances in machine learning may allow even more precise estimates of cell and organ age. One method involves DNA methylation, where chemical groups attach to DNA parts.
Using methylation measurements, scientists can create epigenetic maps comparing biological ages of different tissues and organs. For example, breast tissue in some women ages faster than their actual age, which might explain higher breast cancer rates.
There’s hope that reversing methylation changes could rejuvenate tissues and prevent cancer before it starts.
Can we reverse organ aging?
No matter how we look at aging, the ultimate goal is to slow or reverse it. At the cellular level, this might be possible. In March 2020, Stanford researchers announced they had rejuvenated cells from older volunteers.
They used Yamanaka factors, proteins known to revert cells to an embryonic state. After a few days, cells from older donors looked significantly younger.
But that’s at the cell level. Reversing aging in an entire organ or body is much harder. Some scientists focus on slowing overall aging rather than reversing it.
This approach aims to extend healthy lifespan, or healthspan, rather than just lifespan. A recent University College London study found drugs like rapamycin, metformin, and lithium can delay age-related diseases.
This means these drugs help older people enjoy healthier lives without disease, but they don’t stop or reverse aging itself.
Richard Siow says studying organ-specific aging is valuable because it helps plan health care strategies.
But he notes organ aging can’t be separated from overall system aging since organs influence each other.
“If you have joint inflammation, it also affects your brain and heart,” Siow explains. “Each organ ages differently, but they’re all connected.”
Source: BBC
