For decades, doctors thought the thymus was useless after childhood. This small gland sits in the upper chest, behind the breastbone. In children, it trains immune system cells. Then it shrinks with age and is replaced by fat. Scientists believed it stopped working.
New research challenges this idea. Researchers at Mass General Brigham in Boston studied CT scans from about 27,000 people using artificial intelligence. They discovered that people with a healthier thymus lived longer, and the difference was significant.
The team created a score for thymic health based on size, structure, and composition. They analyzed data from over 25,000 adults in a lung cancer screening trial and 2,500 participants from the Framingham Heart Study, which started in 1948.
The results were striking. People with high thymic health scores had a 50% lower risk of death compared to those with low scores. They also had a 63% lower risk of cardiovascular death and 36% lower risk of lung cancer.
Another study examined cancer patients receiving immunotherapy. Those with stronger thymic health had a 37% lower risk of cancer progression and 44% lower risk of death.
Hugo Aerts, who leads the Artificial Intelligence in Medicine program at Mass General Brigham, explains that computers can find patterns in medical images that humans miss. The thymus, visible on millions of existing CT scans, may have been hiding important information all along.
Research showed that chronic inflammation, smoking, and higher body weight damage thymic health. The thymus appears to reflect overall immune system health rather than directly cause these outcomes. Still, this overlooked gland may prove to be one of the most reliable indicators of how long an adult body will last.