The
most traditional theory: that aging is due to accumulated tissue
damage due to oxidative stress created
by free radicals.
That aging is due to accumulated damage in cellular DNA, leading to cancers, cell senescence or cell death, in turn leading to tissue and organ deterioration.
Mitochondria (energy-producing
organells in cells) are critical
to the cell reproduction cycle and their DNA, different from the cells main DNA, is particularly vulnerable to damage.
With aging, tissues become increasingly damaged and dysfunctional due to cross-linkages with sugar molecules.
Metabolic product gunk called lipofuscin accumulates in cells and inhibits their
functionality.
Chronic inflammation appears to be a core condition underlying many if not most age-related disease processes.
Immune systems weaken with age increasing susceptibility to all kinds of diseases.
Neurological systems weaken with age causing loss of coordination of other body systems.
Hormone levels run down with age and so do all of the body systems they regulate
Risk of cell cancer pathology due to shift in gene expression increases radically with aging
Cardiovascular diseases are the biggest killers of old people
It has been thought that most of the diseases of old age come about through cell senescence due to telomere loss.
Aging is a consequence of programmed shifts in gene expression that happen throughout life.
Aging is due to a slowing rate of organ regeneration because of declining differentiation activity of adult stem cells.