Rapporti ISTISAN 09/49 ISTITUTO SUPERIORE DI SANITÀ Ageing ...

Rapporti ISTISAN 09/49
2.3. Physiological ageing theories
The physiological ageing theories are divided in:
- Stress theory
It describes ageing as the result of the additive effect, over time, of the effects of the
stresses of living. Each time a stress occurs it leaves a residual impairment from which
one does not fully recover. Eventually the cumulative stresses deplete one’s body of
needed reserves (Selye, 1966). The theory ignores the fact that, depending on how one
learns to manage stress, the ability to handle stress and the side effects can actually be
increased and improved.
- Adaptation theory
It attributes ageing to the failure of adaptive mechanisms (Blumenthal & Bems, 1964;
Walford, 1969). For example, as one ages the antidiuretic hormone works less efficiently
in preventing excess loss of body fluid through urination. There are many other ways in
which the body’s physiologic changes with age may evidence failure of adaptive
mechanisms such as (1) the fact that receptor sites important to sugar metabolism are
fewer, (2) breathing capacity diminishes and (3) immune response is thought to decrease.
- Immune system theory
Theories about immunity and autoimmunity go as far back as the researchers Blumenthal
& Berns and Walford. The theories are based on two observations: (1) that the
functioning of the immune system decreases with age, as is autoimmune disease as one
ages. The immune system includes the thymus, spleen, tonsils, bone marrow and
lymphatic system. These produce many substances important to resisting infection
including lymphocytes, antibodies, and interleukins (NIA, 1993).
- Lymphocytes theory
They are of two major types: B-cells and T-cells. B-cells (found in the bone marrow)
secrete antibodies to overcome infections. T-cells are further divided into (1) cytotoxic Tcells
and (2) helper T-cells. Cytotoxic T-cells attack infected or damaged cells directly;
helper T-cells produce chemicals that assist other immune system substances to function. Tcells
are formed in the thymus, which decreases in weight and ability to produce T-cells as
one ages (NIA, 1993). It is known that the interleukins help regulate the immune system.
Researchers have found that interleukin-6 rises with age. It is thought that this increase
interferes with immune system response. Another observation has been that interleukin-2,
which stimulates T-cell production thereby improving resistance to infection, declines as
one ages (NIA, 1993). The decrease in immunological function may result in an increase in
autoimmunological function. There is some evidence that there is an increase in
autoantibodies in older people, which act to destroy normal cells (NIA, 1993).
- Calorie restriction theory
Research done on animals gives some support to the theory that fewer calories are better
than more calories. Mice which were given 30 to 60% fewer calories than the comparison
mice lived longer than the mice on higher calorie diets. Currently, the effect of dietary
calories is being studied in other species and primates (NIA, 1993).
- Behavioural factors theory
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