People who reach 100 aren’t simply surviving longer—they often seem to age differently at a biological level.
Their Immune Systems Can Stay Surprisingly Active
A 2026 review found that many centenarians retain unusually strong immune function despite their age. Some of their immune profiles can resemble those of considerably younger people.
Some Have Large Numbers of Rare Killer T Cells
Researchers studying people aged 110 and older found unusually large populations of cytotoxic T cells, immune cells capable of destroying infected or abnormal cells. Scientists suspect they could help protect against disease, although that connection has not been proven.
They Often Delay Major Diseases
A massive Swedish study following more than 170,000 people found that those who eventually reached 100 generally developed major diseases later—or avoided some of them altogether—rather than simply surviving longer with the same diseases.
Their Bodies May Handle Inflammation Differently
Extreme longevity has been associated with biological mechanisms that appear to limit chronic inflammation, along with stronger cellular maintenance and repair systems. Researchers are studying whether these adaptations help protect tissues over decades.
Genetics Matter, But They Aren’t the Whole Story
A 2026 study of more than 1,500 adults aged 80 and older found that both genetic predisposition and modifiable health factors were associated with longevity. The researchers found the effects worked together rather than one completely determining the outcome.
Scientists Still Don’t Have a Longevity Formula
That may be the strangest finding of all. Researchers increasingly see extreme longevity as a combination of genetics, immune function, metabolism, environment and disease resistance—not one secret habit that explains why someone reaches 100.
Sources
- Nature Reviews Immunology, “The long-lived immune system of centenarians”
- Nature, “How do people live beyond 110? Abundance of cancer-killing cells might be key”
- The Journals of Gerontology, study comparing centenarians with shorter-lived peers
- npj Aging, 2026 study of genetic and modifiable factors associated with longevity
