Sudden, late degeneration

By what looks like a lady on Quora, no particular claim to medical expertise:

“When a 70-year-old marathoner suddenly “falls off a cliff” at 82, it seems their healthy habits failed them. In reality, this rapid decline is the direct result of those habits.

In gerontology, this is known as the compression of morbidity. Unhealthy people often experience a slow, agonizing decline starting in their 50s or 60s, spending decades managing chronic diseases. People with excellent habits delay serious illness for so long that they eventually hit a hard biological wall, compressing all their physical decline into a brief, dramatic window at the very end of their lifespan.

This sudden crash is driven by homeostenosis, which is the age-related loss of physiological reserve. In youth, human organ systems have massive redundant capacity. If a 30-year-old gets a severe flu, their body has the shock absorbers to bounce back. By age 85, even in a perfectly healthy person, the heart, kidneys, and immune system operate near their maximum capacity just to maintain normal resting homeostasis. Because there is zero reserve left, a minor stressor—like a urinary tract infection, a change in medication, or a minor fall—can trigger a catastrophic cascading failure across multiple organ systems.

Beneath this system-wide fragility is a hard cellular limit. No amount of exercise or nutrition can stop cellular senescence.

Human cells can only divide a finite number of times, a boundary known as the Hayflick limit. Every time a cell replicates, the protective caps at the ends of its chromosomes, called telomeres, get slightly shorter. Once those telomeres degrade, the cell enters senescence, refusing to divide and instead secreting inflammatory markers that damage surrounding tissue. Over decades, this microscopic damage accumulates until entire organs lose the ability to repair themselves.

Evolutionary biology offers the final piece of the puzzle through antagonistic pleiotropy. The human genetic blueprint prioritizes traits that guarantee survival and reproduction up to about age 50. After humans pass their child-rearing usefulness, natural selection stops optimizing for tissue repair. The genetic instructions simply run out. A lifetime of healthy habits maximizes a person’s potential within that biological blueprint, allowing them to coast smoothly to the very edge of the map, but it cannot redraw the map itself.”