Hormones act as a biological clock controlling the pace of aging. The immune system breaks down, eventually leaving a person more and more vulnerable to infection and disease. If a person has a high metabolic rate, his or her life span will be shorter. Proteins in the body accumulate. This slows down the body's processes and the body begins to age.
Oxygen radicals accumulate in the body and damage it.
The organs eventually stop working. The mechanism in the body that synthesizes proteins ceases to work well. Faulty proteins are developed and cause damage to cells, tissues, and organs. Genes mutate as the body ages, causing cells to malfunction and deteriorate. Experts used to believe that chronic disease and disability always accompanied aging.