Telomeres (structures at the ends of chromosomes) have experimentally been shown to shorten with each successive cell division. Shortened telomeres activate a mechanism that prevents further cell multiplication. This may be an important mechanism of aging in tissues like bone marrow and the arterial lining where active cell division is necessary.
Reproductive-Cell Cycle Theory
The idea that aging is regulated by reproductive hormones that act in an antagonistic pleiotrophic manner via cell cycle signaling, promoting growth and development early in life in order to achieve reproduction, but later in life, in a futile attempt to maintain reproduction, become dysregulated and drive senescence (dyosis).
Wear-and-Tear theory
The idea that changes associated with aging are the result of chance damage that accumulates over time.
Somatic Mutation Theory
The biological theory that aging results from damage to the genetic integrity of the body’s cells.
Error Accumulation Theory
The idea that aging results from chance events that gradually damage the genetic code.
Accumulative-Waste Theory
The biological theory of aging that points to a buildup of cells of waste products that presumably interferes with metabolism.
Autoimmune Theory
The idea that aging results from an increase in autoantibodies that attack the body’s tissues. A number of diseases associated with aging, such as atrophic gastritis and Hashimoto’s thyroiditis, are probably autoimmune in this way.
Aging-Clock Theory
The theory that aging results from a preprogrammed sequence, as in a clock, built into the operation of the nervous or endocrine system of the body. In rapidly dividing cells the shortening of the telomeres would provide just such a clock.
Cross-Linkage Theory
The idea that aging results from accumulation of cross-linked compounds that interfere with normal cell function.
Free-Radical Theory
The idea that free radicals (unstable and highly reactive organic molecules, also named reactive oxygen species or oxidative stress) create damage that gives rise to symptoms we recognize as aging.
Mitohormesis
It has been known since the 1930s that restricting calories while maintaining adequate amounts of other nutrients prevents aging across a broad range of organism. Recently, Michael Ristow has shown that this delay of aging is due to increased formation of free radicals within the mitochondria causing a secondary induction of increased antioxidant defense capacity.
