mouse The Debate





The Debate




The Debate: Competing Theory of Aging

Although a popular theory, the free radical theory of aging (as supported by the data in the study conducted by Schriner et al) is not accepted by all members of the scientific community. In fact, there are a number of competing theories, which each attribute different biochemical mechanisms as the source of aging in an organism. The following outlines some of these theories briefly.

Telomere Theory of Aging

First observed by scientists at the Geron Corporation, the telomere theory rests on the discovery that telomeres shorten each time a cell divides. This shortening of the telomeres is believed to lead to cellular damage over the years. Each time a cell divides it looses at little more information than it previously had, thereby leading to cellular dysfunction, and eventually, death.1

Neuroendocrine Theory of Aging

It is theorized that “wear and tear” of the neuroendocrine system causes aging. This theory, first proposed by Drs. Vladimir Dilman and Ward Dean, is derived from the observation that as a person ages, the horomones secreted by the hypothalamus in the brain loose their specificity. The hypothalamus looses its regulatory precision and the receptors for the hormones it secretes become less sensitive. It is thought that the horomone cortisol, which increases with age, damages the hypothalamus.1

The Membrane Theory of Aging

According to the membrane theory of aging, aging occurs due to the accumulation of a toxic compound, lipofuscin. The amount of lipofuscin in the body accumulates with the passage of time. Lipofuscin can be found in the skin pigmentation of so-called “age or liver-spots.” The lipofuscin deposits in the body eventually lead to cell inefficiency and death.1

The Hayflick Limit Theory of Aging

Named after its discoverer Dr. Leonard Hayflick, the Hayflick Limit Theory of Aging proposes there is a limit to the number of times a human cell can divide. This limit, according to the theory, exists as a result of waste accumulation.1

The Cross-Linking Theory of Aging

Also referred to as the glycosylation theory of aging, the cross-linking theory, suggests that the binding of glucose to protein, which occurs in the presence of oxygen, causes aging of the cell to occur. Binding glucose to proteins is called “cross linking.” Once glucose has bound to a protein, the protein becomes impaired.1

Although the aforementioned theories are supported by many scientists, the free radical theory of aging is the most widely accepted theory. Not only scientists, but also lay people, have taken a particularly strong interest in this theory, as evidenced by the sales of supplemental antioxidants. It is arguably the most prominent theory of aging in the scientific literature today.


University of Arizona
Biology 181H 2005 Group 7
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Last Revised: 12/7/05