We die of old age primarily because our cells progressively lose their ability to function properly and divide, a state called cellular senescence. Over time, this leads to deterioration of tissues and organ function. Key biological factors include the shortening of telomeres (the protective ends of chromosomes) with each cell division, accumulation of DNA damage, oxidative stress from reactive oxygen species, and the build-up of cellular waste products. The immune system also weakens, contributing to higher vulnerability to diseases. Ultimately, this gradual decline results in the failure of critical organ systems, causing death.

Cellular Senescence and Telomere Shortening

Cells have a natural lifespan, and with age, their protective telomeres shorten, limiting their ability to divide and regenerate. When cells stop dividing, they either die or become senescent, which triggers inflammation and tissue dysfunction, accelerating aging.

Oxidative Stress and DNA Damage

Metabolic processes produce reactive oxygen species (ROS), which damage cell membranes, proteins, and DNA. Over time, this oxidative damage accumulates, leading to impaired cell function and increased risk of diseases like cancer and cardiovascular conditions. The body’s repair mechanisms become less efficient as we age.

Immune System Decline

With age, the immune system deteriorates (immunosenescence), reducing its ability to fight infections and increasing chronic inflammation. This decline contributes to vulnerability to diseases that often cause death in elderly people.

Organ Failure as the Final Cause

Death from old age is usually the result of failure of major organs such as the heart, lungs, or kidneys due to accumulated damage and decreased regenerative capacity. This organ failure often goes by named causes like heart disease or pneumonia, linked to the aging processes described.

Thus, dying of old age is caused by a combination of genetic, cellular, metabolic, and environmental factors leading to the gradual decline of body functions, culminating in organ failure and death.