Theories Of Aging
The process of aging is characterized by imbalances that result in dysfunction manifested at different biological levels and culminate in death of the organism. Some of these changes are programmed and begin from within the cell, and others occur in response to the intrinsic or extrinsic environment. Stress is an important concept in many theories of aging, including systemic, cellular, and molecular theories, and especially in those which explain aging in terms of ability to maintain and restore homeostasis. However, the effects of prolonged stress on an individual may be due to the development of disease and not a result of normal aging process. Questions that remain are whether the effects on aging are due to stress or to stress-induced disease processes that overwhelm the defense or repair systems, and are then life-threatening in old individuals. With these caveats in mind, the stress response is important in the neuroendocrine theory of aging and oxidative stress is important in the free radical theory of aging.
New humoral or systemic factors are being described that differentially regulate the cellular stress response during aging. As shown by studies from Dan Hultmark’s group in Sweden, a humoral factor that increases heat shock protein 70 prevents cell death and restores stress resistance in old cells. These factors implicate neural and endocrine signals in the control of aging. The neuroendocrine theory of aging proposes that the ability to respond to stress is an important factor in reduced ability to maintain homeostasis during aging. Furthermore, the control of homeostasis becomes disorganized during aging, resulting in loss of adaptive capacity, decreased resistance to stress, and increased allostatic load. Thus, aging is the price the organism has to pay for surviving stress. Convincing evidence supports the theory that free radicals and oxidative stress play an important role in the aging process, and indicates that oxidative damage to neurons may be related to life span and aging, as well as to neurodegeneration. This knowledge may be used to find ways of slowing aging and increasing average life span in humans.