Theories of Ageing

Original Editor - Bhanu Ramaswamy as part of the AGILE Project.

Top Contributors - Wendy Walker, Lucinda hampton, Venus Pagare, Admin, Bhanu Ramaswamy, Vidya Acharya, Lauren Lopez, Kim Jackson, Jasrah Javed, Scott Buxton and Christina Nowak  

Ageing

Most people will live to experience ageing. Up until ten years ago, maximum life span (the maximum biological limit of life in an ideal environment) was not thought to be subject to change; it was set in the 1960’s by Hayflick at around 115 years. Life span is considered the key to the intrinsic biological causes of ageing, as these factors ensure an individual’s survival to a certain point until biological ageing eventually causes death. 

There are many theories about the mechanisms of age related changes, and they are not mutually exclusive. Gershon and Gershon have split them in two main groups:

1. Genetic Programming

Genetic programming (biological clocks) is a built-in programme in the genome is activated at a certain stage of an organism’s life cycle, and leads to death via a self-destruct mechanism. There are two major lines of research in genetic theories.

• The Hayflick limit: Cells divide for a set number of times, and then become senescent.
• Telomere loss and ageing: These are repeat sequences of DNA and protein which protect the ends of chromosomes from degradation and fusion with one another 

2. Stochastic Events

Stochastic events, random damage and errors of repair (wear and tear) – random damage accumulates throughout the lifespan and this damage gradually causes a reduction in the efficiency of the overall function of the organism and eventually results in its demise. In 1956, Denham Harman proposed the theory that ageing is caused by an accumulation of molecular damage caused by "oxidative stress", the action of reactive forms of oxygen, such as superoxide, on cells. Although the theory dominated the field of ageing research for over fifty years, it still leaves gaps in that field of research.

Most evidence for ageing mechanisms is related to a reduced ability to repair and maintain the cell, however, Gershon and Gershon note that often there is poor distinction and confusion made between primary causes of ageing and secondary age-associated phenomena. Experimentation is also laboratory-based negating environmental influences on the subject, affecting the experiment outcome. It is still uncertain to what extent the mechanisms governing ageing are genetically determined.

The mechanism of the actual ageing process remains elusive. The current theories show ageing to be a multi-factorial process governed by a multitude of parallel and often interacting processes. Many are controlled jointly by a combination of genetic and environmental factors.

3. Disengagement Theory

• Refers to an inevitable process in which many of the relationships between a person and other members of society are severed & those remaining are altered in quality.
• Withdrawal may be initiated by the aging person or by society, and may be partial or total.
• It was observed that older people are less involved with life than they were as younger adults.
• As people age they experience greater distance from society & they develop new types of relationships with society.
• In America there is evidence that society forces withdrawal on older people whether or not they want it.
• Some suggest that this theory does not consider the large number of older people who do not withdraw from society.
• This theory is recognized as the 1st formal theory that attempted to explain the process of growing older.
  

4. Activity Theory

• Is another theory that describes the psychosocial aging process.
•  Activity theory emphasizes the importance of ongoing social activity.
  
•  This theory suggests that a person's self-concept is related to the roles held by that person i.e. retiring may not be so harmful if the person actively maintains other roles, such as familial roles, recreational roles, volunteer & community roles.
• To maintain a positive sense of self the person must substitute new roles for those that are lost because of age. And studies show that the type of activity does matter, just as it does with younger people.
  

5. The Neuroendocrine Theory

First proposed by Professor Vladimir Dilman and Ward Dean MD, this theory elaborates on wear and tear by focusing on the neuroendocrine system. This system is a complicated network of biochemicals that govern the release of hormones which are altered by the walnut sized gland called the hypothalamus located in the brain.
The hypothalamus controls various chain-reactions to instruct other organs and glands to release their hormones etc. The hypothalamus also responds to the body hormone levels as a guide to the overall hormonal activity. But as we grow older the hypothalamus loses it precision regulatory ability and the receptors which uptake individual hormones become less sensitive to them. Accordingly, as we age the secretion of many hormones declines and their effectiveness (compared unit to unit) is also reduced due to the receptors down-grading

6. The Free Radical Theory

• This now very famous theory of aging was developed by Denham Harman MD at the University of Nebraska in 1956. The term free radical describes any molecule that has a free electron, and this property makes it react with healthy molecules in a destructive way.
  
• Because the free radical molecule has an extra electron it creates an extra negative charge. This unbalanced energy makes the free radical bind itself to another balanced molecule as it tries to steal electrons. In so doing, the balanced molecule becomes unbalanced and thus a free radical itself.
• It is known that diet, lifestyle, drugs (e.g. tobacco and alcohol) and radiation etc., are all accelerators of free radical production within the body.

7.The Membrane Theory of Aging

The membrane theory of aging was first described by Professor Imre Zs.-Nagy of Debrechen University, Hungary. According to this theory it is the age-related changes of the cells ability to transfer chemicals, heat and electrical processes that impair it.
As we grow older the cell membrane becomes less lipid (less watery and more solid). This impedes its efficiency to conduct normal function and in particular there is a toxic accumulation

8. The Mitochondrial Decline Theory

• Next Page - Policy and Initiatives Focused on the Older Population