Theories of ageing

1. Theories of
Ageing

2. AGEING
 Ageing is a lifelong process of growing up and growing
old.
 Begins at conception and ends with death.
 Chronological Aging is the number of years a person
has lived so far.
 Biological aging is that aging occurs as you gradually
accumulate damage to various cells and tissues in the
body.
 Psychological Aging involves changes in memory,
learning, intelligence, personality, and coping.
 Social Aging refers to changes in roles and relationships
as individual age.

3. Theories of Ageing
Each theory of aging attempts to provide a framework to
understand aging from different perspectives.
Biologic theories of aging aims to explain why the
physical changes of aging occur.
There are two primary categories of aging; these
include:
• Programmed theories - Programmed theories believe that
aging is a normal process, just as puberty is a normal
developmental process.
• Error theories - Error theories believe that aging is not
something which is programmed to occur, but rather
aging is due to a series of "accidents."

4. Theories of Ageing
Some general theories of aging related to nutrition aspects are:
Neuroendocrine and hormonal theory
Free radical theory
Calorie restriction theory
Immunological theory
Wear and Tear theory
Clinker theory

5. Free Radical Theory of Ageing
Given by Denham Harman in 1950s.
 He studied that- lifespan is an inverse function of
metabolic rate which in turn is proportional to oxygen --------
consumption
 He proposed that:
 cells continuously produce free radicals by normal metabolism
and oxidation of organic compound
 these free radicals damage cellular components (membrane) and
macromolecules (DNA, lipid, protein)
 accumulation of these damage over time
period cause aging.
Free radical structure

6. In 1972s, Denham Harman modified his theory-
About 95% energy of a cell is produce in mitochondria.
97-99% of oxygen is used in energy formation and 1-3%
utilized in reactive oxygen species formation.
Theory states that:
Reactive oxygen species (ROS) are produce in mitochondria
during ETC cycle cause damage to macromolecules (lipid,
protein, DNA) of mitochondria and nucleus leading to aging.
Contd…….
Mitochondrial Free Radical theory

7. Criticism of free radical theory:
Main criticism- all free radicals are responsible for
damage biomolecules which must be major reason for
cell aging which is not true because:
 Many reactive oxygen species participate in signaling
pathway.
 Many free radicals kill and inject harmful bacteria.
 Many free radicals are co-factor of enzyme and protein
derivatives.
Contd…………..

8. Calorie Restriction Theory
Calorie restriction defined as reduction of energy intake
without malnutrition.
This theory of ageing is proposed by David Sinclair
(2005)- considered that CR is not a simple and has passive
effect.
 CR diet total amount of food is reduced but major
nutrients, minerals and vitamins required for health are
maintained.
 Gradual lose weight until maximal efficiency retards
aging.
 Experimental mammalian models of CR reduce calorie
intake by 40% throughout lifespan of animal.

9. • Results: CR proved to be beneficial at various
level of functions and involving a number of
molecules, cellular and systematic changes.
• Calorie restriction diet influences both aging
rate and disease susceptibility.
Limitation: Some studies revealed that calorie
restriction affects immunity and slow the DNA
repair capacity
Contd….

10. Neuroendocrine and hormonal theory
Neuroendocrine cells are chemical messengers of the
endocrine system, passing signals from one neuron to the
next, and from a neuron to a target cell across a synapse.
This theory is proposed by Vladimir Dilman
Theory states that “The effectiveness of the body's
homeostatic adjustments declines with aging—leading to
the failure of adaptive mechanisms, aging, and death.
Also called as aging clock theory and the pacemaker theory

11. Contd……
 This theory view the functional decline in neurons and
their associated hormones as central to aging.
 Give the major role- neuroendocrine system in physiology.
 This is an attractive theory of aging and neuroendocrine
disease
 In humans, aging is associated with decreased production
of hormones, amino acids, peptides, monoamines, and
enzymes.

12. Contd……
According to this theory, ageing is mediated in brain.
Dilman based his theory on past studies of
hypothyroidism- a disease that mimics mature aging
He proposed that the hypothalamic, pituitary and
adrenal axis is the master timekeeper for the organism
and primary regulate aging process.

13. Contd……
Criticism:
 Critics of the neuroendocrine theories point out that the master
timekeeper of aging – the neuroendocrine system – lacks
universality.
 Many organisms that age (e.g., higher vertebrates) have no
complex neuroendocrine system.
 It can also be argued that the changes in the neuroendocrine
system are expected and occur in all tissues.

14. • Proposed by Walford
• This theory asserted that the process of human aging
involves a highly complex series of processes which are
suspected to be largely controlled by the immune system.
• Basis: As humans age, they experience changes to almost
all physiological functions, including those related to the
immune system.
• Theory explain rate of aging is controlled by the immune
system which declines.
Immunological theory

15. • It is based on two major observations:
1. The immune system weakens over time, making an aging
person more susceptible to disease, increase in
autoimmune disease and allergies.
2. Over time, cells involved in immune function are less
self-regulatory, resulting in cells being misidentified as
foreign material and being attacked by the immune
system’s own defenses.
• Example: rheumatoid arthritis (RA) and lupus.
Contd…….

16. Limitations:
Its difficult to defend the immune system’s
role as the primary time keeper in biology of
all organisms.
Contd…….

17. Wear and Tear theory
 Proposed by Dr. August Weismann.
 This theory asserts that the effects of aging by progressive
damage to cells and body systems over time.
 This may be referred to as simple deterioration theory or
fundamental limitation theory.
 Long term damage to cells, tissues and organs eventually wear
them out, killing both them and the body.
Ex: wearing out of the skeletal system such as in osteoarthritis.
 Wear and tear can be viewed as a result of aging and not the
cause of it.
 With age, body’s mechanism to repair the damage caused by wer
and tear get reduced.

18. Contd………..
Criticism:
Cells are well-equipped to repair damage.
 Humans and other organisms grows stronger from
youth to maturity.
Organisms vary widely in lifespan rather than all
following the same pattern.

19. Clinker theory
• This theory combines the somatic mutation, free
radical and cross links in DNA
• Due to metabolism process, potentially harmful
substances get accumulate in the body over the
years
• These substances cause damage to body organs
such as muscles, heart, nerves and brain
• One substance that has been identified is
LIPOFUSCIN.

20. Contd……….
• Lipofuscin is a mixture of chemical waste
products from normal cellular activities which
becomes concentrated in the cells of the body
e.g. heart and brain
• High lipofusin concentrations make cells appear
darker in colour- age pigment
• Accumulation of glucose has been implicated in
causing them to stick together