Aging is a complex subject. It is a natural aspect of life, yet it is often feared and one that many individuals try to prevent. Aging can be viewed from many different perspectives. The following is an overview of the main theories of aging.
- 1 Aging Theories
- 1.1 Historic Views of Aging
- 1.2 Biological Aging Theoreis
- 1.3 Psychological and Social Aging Theories
- 1.4 Psychological Theories
- 2 Treatment Strategies
- 3 References
Historic Views of Aging
Theories about aging have been around for more than 2,000 years. Some of the original theories of aging included:
- Galen (A.D. 129 - c.199). His theory was based on the idea that aging was due to changes in the body humors that began early in life. Overtime the body became more dry and cold which resulted in the symptoms of aging.
- Roger Bacon (c. 1220-1292) was one of the first to introduce the concept of aging due to wear and tear on the body. Aging was believed to be the result of abuses and insults in the body systems. It was during this time that hygiene was introduced as one way to delay the aging process.
- Charles Darwin (1809 - 1892) attributed aging to decreased in function of the nervous and muscular tissues.
- Elie Metchnikoff(1904), a Russian immunologist, re-introduced the wear and tear theory and he also was the first to link aging to the toxins released by bacteria in the intestinal tract. He introduced the idea of eating yoghurt as an antidote to the toxic bacteria in the intestines.
Biological Aging Theoreis
"Senescence or biological aging is the process of accumulative changes to molecular and cellular structure that disrupts metabolism with the passage of time, resulting in deterioration and death. Senescence occurs both on the level of the whole organism (organismal senescence) as well as on the level of its individual cells (cellular senescence)." 
Programmed (Genetic Cellular) Theories
As mammals of each species have a similar life span, despite considerable diversity among different species, the notion of genetic control of life span is a widely accepted theory. Ideas that support this theory include:
- Growth, reproductive maturity and other biological functions are programmed. It stands to reason that aging would be as well.
- Individuals that have parents and grandparents that lived a long time tend to live about 6 years longer than those whose parents died before the age of 50.
- Tissue cultures of human body cells are only able to divide about 50 times before they age and die.
- The reproductive capacity of cells taken from old animals can undergo only about 1/2 as many divisions as those obtained from young animals.
- DNA/RNA Damage Theory or Error Theory
The DNA/RNA Damage Theory relates aging to damage to the DNA or RNA molecules. The notion behind this theory is that there is an innate programmed mechanism that sets the duration of life and ensures that there is sufficient turnover in human life to allow room for the young.
- Aging occurs due to cellular-point mutations that accumulate over time. Radiation and other environmental toxins may add to the risk of DNA damage.
- Errors in RNA transmission produce a protein or enzyme that is not an exact copy of the original, thus it cannot carry out its function in maintaining life. As a result cells grow old and die.
- RNA errors are more common as RNA molecules are formed continuously and relatively unstable.
- Telomerase Theory 
- At the ends of the chromosomes are stretches of DNA called telomeres, which protect our genetic data, making it possible for cells to divide.
- Aging appears to be correlated with decreased length of the telomeres.
- Telomeres shorten with each cell division. It is believed that nutritional imbalances and environmental toxins may also impact the length of telomeres.
Physiological System Theories
Physiological Theories attribute aging to the gradual failure of certain physiological systems and the inability of the body to coordinate bodily functions. At times, physiological theories of aging are associated with programmed theories of aging.
- Free Radical Theory
The free-radical theory was introduced by 1954 by Dr. Harman from the University of Nebraska.
- Aging occurs when cells become permanently damaged from the life-long and unrelenting attack of charged molecular fragments, referred to as free radicals.
- Free radicals can attack the membrane fats causing a breaking down of cell membranes, it can attack red blood cell membranes causing hemolysis or it can cause the breakdown of proteins within the body or even the breakdown of DNA resulting in DNA mutations.
- When free radicals attack the structure of cell membranes it can result in the accumulation of metabolic waste products, including substances known as lipofuscins. An excess of lipofuscins in the body shows up at darkening of the skin or age spots, also known as liver spots.
- 80% to 90% of all degenerative diseases involve free radical activity and oxidative stress.
- Environmental toxins such as industrial waste, chemical residues, pesticides and herbicides, automobile exhaust, cigarette smoking, processed food and preserved meats, alcohol, beverages such as coffee and other forms of ionizing radiation increase the risk of free-radical damage.
- Endocrine Theories
The endocrine systems represent the body's "hormonal clock". The endocrine theory states that the biological clocks act through hormones to control the pace of aging.
- All endocrine systems are inter-related. All hormones, such as corticosteroids, insulin, growth hormone and sex hormones are under the control of the endocrine system. Hormones work together to regulate development, sex drive, puberty, menopause and other physiological processes including our responses to heat and cold, stress and sexual activity. It also controls metabolic rate, glucose secretion and water levels.
- Aging is associated with decrease in hormones including circulating sex hormones such as estrogen, testosterone, dihydroepiandrosterone (DHEA), melatonin and growth hormones and insulting-like growth hormone.
- Changes in the hypothalamic-pituitary-adrenal (HPA) axis due to stress may contribute to aging. The HPA axis is one of the body's two major endocrine regulatory systems for responding to stressors and maintaining internal homeostatic integrity.
- Immune Theories
The immune system protects an individual from invading pathogens and atypical mutant cells that form within the body. A breakdown in the immune system is associated with age-related changes in the body. The Immune Theory of aging states:
- The immune system is programmed to decline over time, which leads to an increased vulnerability to infectious disease and thus aging and death.
- The effectiveness of the immune system peaks at puberty and gradually declines thereafter with advance in age. As the immune system function declines the body's ability to fight off pathogens decreases, antibodies lose their effectiveness, and hence fewer new diseases can be combated effectively, which causes cellular stress and eventual death.
- Dysregulated immune response has been linked to cardiovascular disease, inflammation, Alzheimer's disease, and cancer.
- Aging is caused by a decline in the immune system's ability to discriminate self from non-self.
- The thymus gland declines in size from infancy (250 gm) to adulthood (3 gm). Age-related reduction in the size of the thymus gland corresponds to the reduction in the immune system function.
Non-programmed (Non-Genetic Cellular) Theories
There are a number of non-programmed theories associated with aging. These theories are relate to the accumulative deterioration of bodily processes and include:
- Wear and Tear Theory
The Wear and Tear Theory, also known as Deterioration Theory was first proposed by Roger Bacon in the 12th century. It was re-introduced by Elie Metchnikoff in 1904 and again in 1982 by Weissmann. It is also referred to as the Rate-of-Living Theory.
- The daily grind of life, in particular abuses or overuses wears the body out, eventually leading to disease states and aging.
- Aging is the result of progressive cell damage and loss of function caused by both the internal and external environment, rather than to programmed cell damage and death.
- The greater an organism's basal metabolic rate, the shorter the life span.
- This theory is often linked to the free radical theory.
- Waste Accumulation Theory
- Aging is the caused by the accumulation of various harmful substances and waste products either as a consequence of normal metabolic processes or due to increased exposure. These waste products or cellular garbage interferes with cellular functioning and gradually destroys the cell.
- Older cells contain a dark coloured, insoluble substance called lipofuscin which consists of oxidized (rancid) fats that accumulate in the skin and internal organs. Liver spots, or age spots are an example of lipofuscin and they continue to accumulate over time, if not addressed.
- Faulty Reconstruction Theory
- The body is in a constant state of repair and regeneration. The faulty reconstruction theory states that aging results in the repair and regeneration processes of the body breaking down over time resulting in faulty reconstruction. This overtime weakens the cells and impairs their cellular function.
- Cross Linkage Theory and Mitochondrial Damage Theory
The Cross-Linkage theory was first introduced in 1942 by Johan Bjorksten. It is based on the concept that increases in glycation increases aging. Glycation is the result of inappropriate attachments or cross-links to other molecules.
- The molecular cross-linking between protein molecules, such as collagen found in our skin, tendons and ligaments and the glycation (cross-linking) of other structural proteins and lipids (fats) and excess glucose, disrupts the function of these molecules, leading to acceleration of the aging process.
- Increases in cross-linkage is associated with the inability of the body to get rid of excess glucose molecules in the blood.
- Glycation results in microvascular changes in arteries, loss of flexibility of connective tissues and decreased mobility or elasticity of proteins and other molecules. Conditions associated with increases in cross-linkage and increased glycation include atherosclerosis, decreased kidney function, cataracts, wrinkling and other signs of aging on the skin.
- Oxidative processes within the mitochondria damage the organelle and result in a decrease in function.
- Rate of Living Theory
The Rate of Living Theory has also been referred to as the Life Time Energy Potential (LEP) Theory.
- In 1908 Max Rubner was the first to observe that mass specific metabolic output of mammals was the same, irrespective of their different size and longevity. In 1928, Raymond Pearl furthered this notice and asserted that maximum life span is inversely proportional to basal metabolic rate.
- In 1970 Hans Selye proposed the idea that there was a fixed amount of adaptive energy. Aging was a result of this adaptive energy being used up by stressors.
- The life time energy potential (LEP) for each mammal is constant. For example, a squirrel living its full 7 years will consume around 60,000 I O2/kg; likewise, a 500 kg horse over its full 35 year period will also consume around 60,000 I O2/kg.
- Regardless of body weight, mammals average the same number of heartbeats within their life. Per unit mass they metabolize the same amount of glucose, synthesize the same amount of protein and they pump the same volume of blood.
- This theory also notes that the higher the temperature, the shorter the lifespan.
- In short, this theory states live fast; die young.
Psychological and Social Aging Theories
All Psychological and Social Aging Theories acknowledge that there is a well-established reduction in social interventions observed in old age. The rational for this correlation is what is debated and argued in these different theories.
In 1961 the disengagement theory was introduced by Cumming & Henry.
- The belief is that impending death stimulates a mutual psychological withdrawal between the older person and their society.
- Cumming and Henry outlined nine postulates. An example of the postulates are:, 
- The expectation of death is universal. As a result, a severing of ties between a person and his society is inevitable.
- Severing ties is a way of freeing oneself from the expectations imposed by interactions and decreases a person's social responsibilities.
- Disengagement differs between men and women. Women tend to have more of a socioemotional role.
- Aging can cause a deterioration of knowledge and skill. In industrialized societies which demand a certain level of knowledge and skill, disengagement is either prompted by ego changes in the individual or by the organization that an individual is associated with, or by both.
- The readiness for disengagement between an individual and society are not always in sync. When the individual is ready and society is not, engagement usually continues. When society is ready and the individual is not, disengagement generally happens.
- The disengagement theory has not been overly supported by research.
In 1968 the Activity Theory was introduced by Havighurst, partly as a rebuttal to the Disengagement Theory.
- Healthy aging is associated with continued psychological and social participation throughout a person's life.
- Inactivity and lack of participation is a societally induced problem stemming from social norms. Disengagement is not compatible with health aging.
- Current research has not found a relationship between activity level and life satisfaction in older adults.
In 1989 the Continuity Theory was introduced by Atchley..
- The Continuity Theory holds that, in making adaptive choices, middle-aged and older adults attempt to preserve and maintain existing internal and external structures; and they prefer to accomplish this objective by using strategies tied to their past experiences of themselves and their social world. Change is linked to the person's perceived past, producing continuity in inner psychological characteristics as well as in social behavior and in social circumstances. Continuity is thus a grand adaptive strategy that is promoted by both individual preference and social approval.
The Scaffolding Theory of Cognitive Aging
In 2008 the Scaffolding Theory of Cognitive Aging (STAC) postulated that functional changes with aging are part of a lifespan process of compensatory cognitive scaffolding that is an attempt to alleviate the cognitive declines associated with aging. Other concepts in theory include:
- There are declines with age in speed of processing, working memory, inhibitory function, and long-term memory, as well as decreases in brain structure size and white matter integrity. In the face of these decreases, functional imaging studies have demonstrated, somewhat surprisingly, reliable increases in prefrontal activation. 
- Neuro-imaging studies have revealed selective changes in the aging brain that reflect neural decline as well as compensatory neural recruitment. 
Socioemotional Selectivity Theory
In 1992 the Socioemotional Selectivity Theory was introduced by L. Cartensen.
- Reduction in older person's social networks and social participation should be seen as a motivated redistribution of resources by the elderly person.
- Social exchanges and interactions are reduced over time.
- People become more selective with whom they choose to spend their time.
- Emotional closeness may become more important with significant others -- quality versus quantity.
Life Span Development Theory
This theory was developed by Bales and Smith in the 1970s and encompasses three principles:
- Evolutionary selection benefits with age.
- The need for culture increases with age.
- The efficacy of culture decreases with age.
Psychological Theories look at psychological development and personality traits either from the perspective of stages or from the perspective of qualities and characteristics.
Erikson's Stages of Psychological Development
In the 1950s Erikson's theory of the stages of psychological development included eight (8) categories or stages of development, six which focuses on development prior to the age of 25.
- "At each stage, the person confronts, and hopefully masters, new challenges. Each stage builds upon the successful completion of earlier stages. The challenges of stages not successfully completed may be expected to reappear as problems in the fucture." 
- At each stage a person is faced with a psychological crisis involving two conflicting forces. Successful completing each phase adds to the person's overall strength and coping skills. You do not have to successfully complete a level in order to move onto the next.
- Older individuals pass through a stage of reflection and self worth. The conflict at this stage is between ego integrity and despair. A positive appraisal results in ego integrity and sense of satisfaction with accomplishment; a negative appraisal and a sense of regrets or having made the wrong decisions results in despair. Those with ego integrity go on accept their mortality and acquire wisdom. Those who fall into despair may become withdrawn and ambivalent or hostile and destructive in their old age.
- Follow this link for a look at the different stages .
Peck's Theory of Ego Integrity
In 1968 Robert Peck identified three developmental stages that elderly go through to reach full psychosocial development.
- Stage 1: Ego Differentation vs. Work Role Preoccupation
- As a person ages they often move from defining themself through their work or occupation to finding new meaning and value in their life through family, friendship, and community life.
- Stage 2: Body Transcendance vs. Body Preoccupation
- At this stage a person either ends up dwelling on their health issues (body preoccupation) or they accept their limitations.
- Stage 3: Ego Transcendance vs. Ego Preoccupation
- This stage is about assessing the impact that a person has made in their life. Ego Transcendance refers to believing that one's life has been worthwhile and their contributions will live on after their death. Ego Preoccupation occurs when a person feels that their life has been useless.
Five (5) Personality Traits
In contrast to the theories of psychological development based on passing through stages, this theory proposes that there are five traits that follow a person throughout their life. These traits dispose an individual to particular thoughts, feelings and behaviours.`, 
- Personality traits may be more stable later in life, whereas goals, values, coping styles and beliefs are more likely to change.
- The five personality traits include:
- Neuroticism refers to a individual`s level of anxiety, hostility, impulsiveness and self-consciousness.
- Neuroticism and conscientiousness tend to result in a greater disease burden. The higher the impulsiveness facet of neuroticism, the stronger it predicts the development of disease, or progression of disease, over time.
- Extroversion is characterized by assertiveness, excitement seeking, and positive emotional experiences.
- Extroversion is in contrast to introversion. These qualities generally remain stable through adulthood.
- Openness to Experience
- Individuals that seek out and are open to new experiences when young are likely to engage in new experiences as they age.
- Openness decreases as one develops chronic illness.
- Agreeableness is in to antagonistic behaviour.
- Neuroticism and conscientiousness tend to result in a greater disease burden.
- These five personality traits are more likely to remain stable throughout a person`s life, especially after the age of 30. Dramatic changes in personality traits may be the result of a traumatic life event or it may indicate an underlying pathology.
- Other personality traits, such as gender roles become less distinct as a person ages, especially once individuals retire and are no longer raising a family.
- Generally speaking, older adults experience less anxiety and depression than younger adults.
With the diversity of factors affecting aging there is a lot of debate on the effectiveness of any specific treatment, yet the following treatments and naturopathic interventions may be beneficial in addressing specific aspects of aging and/or slowing down the aging processes associated with many chronic diseases such as diabetes, alzheimer's disease, heart disease, and dementia.
- Calorie Restriction
Some research indicates that both lifespan and metabolic potential can be modified by caloric restriction.
- http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2995895/ 
- http://longevity-science.org/Evolution.htm 
- http://www.ncbi.nlm.nih.gov/pubmed/1383768 
- Schroots JJ. Theoretical developments in the psychology of aging. Gerontologist.;1996 Dec;36(6):742-8.
- Atchley RC. A continuity theory of normal aging. Gerontologist. 1989 Apr;29(2):183-90. 
- Goh JO, Park DC. Neuroplasticity and cognitive aging: the scaffolding theory of aging and cognition. Restor Neurol Neurosci. 2009;27(5):391-403. 
- Park Denise, Reuter-Lorenz Patricia. The Adaptive Brain: Aging and Neurocognitive Scaffolding Annu. Rev. Psychol. 2009;60:173–96 
- http://www.pearsonhighered.com/showcase/berkexploring2e/assets/Berk_ch18.pdf 
- Sutin AR, Zonderman AB, Ferrucci L, Terracciano A. Personality Traits and Chronic Disease: Implications for Adult Personality Development. J Gerontol B Psychol Sci Soc Sci.;2013 May. PMID: 23685925
- Martin SL, Hardy TM, Tollefsbol TO. Medicinal Chemistry of the Epigenetic Diet and Caloric Restriction. Curr Med Chem. 2013 Jul 24.