Aging is a complex phenomenon dependent upon the interplay of multiple factors including our inherent gentic make-up, developmental factors, environmental influences and the intrinsic aging process. It is a continuum, starting at birth and ultimately ending in death. As we uncover more about the underlying mechanisms of aging, we are better able to realize the true potential and possibilities for both preventive and therapeutic interventions.
Several Theories of Aging have been advanced in an attempt to shed some light on this elusive process we call aging. These Include:
• The DNA / Genetic Theory
Our DNA is a genetic blueprint inherited from our parents. We are therefore born with a unique genetic code which determines the tendency for certain factors affect the rate at which we age. Thus, DNA damage can be thought of as a cumulative phenomenon based on our lifestyle, diet, exposure to certain toxins, pollutants, UV radiation and/or other environmental influences. In addition, as we age, the mechanisms responsible for the repair of genetic damage become less effective. This genetic damage can result in the production of abnormal proteins and sugar-protein complexes (referred to as Advanced Glycation End-Products or AGEs) which can lead to defective functioning of the proteins with a loss of elasticity and stiffening of the cell walls and organs, all common features of aging.
• The Neuroendocrine Theory
This theory suggests that the aging process is programmed by the brain, via the Hypothalamic-Pituitary System, which regulates the release of key hormones which influence cell metabolism, protein synthesis, immune function and the neuronal and biochemical functioning of all the cells in the body. As we age, the hypothalamus loses it's precise regulatory ability and the secretion of many of these hormones gradulally decreases and becomes less effective, leading to hormone imbalance and eventual aging.
• The Free Radical Theory
The production of energy by every cell in the body (via a process called Cellular Respiration), is required for the sustenance of life. Environmental Toxins, Air Pollution and Ultraviolet Radiation, as well as diet, tobacco and alcohol, all result in the production of highly reactive cellular by-products called Free Radicals. These free radicals attack the structures of the cell, resulting in the accumulation of toxic metabolites interfering with cell membrane function and DNA / RNA Protein Synthesis, thus decreasing cell energy production and potentially accelerating the aging process.
• The Immune Theory
As we age, there is a gradual decrease in the functioning of our immune system. The thymus gland (which is partially responsible for the production of cells that protect us from the development of infections, cancer and immune disorders) decreases in function by 80-90% by the time we reach middle age. As we age, our immune system is less able to produce sufficient numbers of antibodies and adequate natural immune defense cells (macrophages and NK cells) as well as an increased tendency to produce antibodies driected against one's own cells - a condition referred to as an Auto-Immune Disorder. As a result, the functional capacity of our immune system declines making us more susceptible to the ravages of the aging process.
• The Telomerase Theory
The cells in our body will normally divide approximately 50 times before they simply stop dividing and eventually die. Based on this theory, there is a gradual deterioration of our body over time secondary to a decrease in the number and functioning of our cells. A possible explanation for this pre-programmed cell death is due to a cap - a Telomere - on the end of each of the 23 pairs of chromosomes that make up the human genome. Chromosomes are the thread-like structiures of DNA found in the nucleus of all cells, carying genetic information in the form of genes. Telomeres can be compared to the plastic cap on the end of a shoelace. Each time the cell divides, the cap (Telomere) shortens. After a specific number of cell divisions, the telomere is whittled away and the end of the chormosome becomes frayed (just like a shoelace) and stops dividing, leading to cellular dysfunction and cell death (Apoptosis). Over time, this cumulative cell death (senescence) contributes to the aging process. In 1989, an enzyme was discovered which could prevent the shortening of the Telomere. This enzyme was called Telomerase. Telomerase acts to repair the damage to telomeres and helps to maintain the telomere's length and stability prolonging the ability of the cell to continue dividing. Telomerase could hold the key to unlocking the mystery of aging by its ability to prolong cell division and slow down or even reverse the aging process.