5. Theories of aging

Aging is a series of changes that occur as we get older and that cause loss of bodily functions eventually causing death. Currently, there is no single universally accepted theory to explain this process.

One of the biological theories on aging is the free radical theory, which began developing Gerschman and Harman (though they weren't the only).

To begin to explain the theory, the first thing we need to know is that free radicals are unstable molecules produced by normal cellular metabolism or after exposure to radiation and contamination.

These molecules, in addition to be the causative of several of cellular oxidative processes (by reaction of oxygen with organic substances) react with various enzymes and proteins causing a disorder of the capacity of the cell to function normally, so that tissues are damaged body and the outer cell membranes. All this leads to a cumulative effect of free radicals and a decrease in physical availability of antioxidants.

Besides all this, it's known that free radicals also have an effect on DNA, since we don't have all the DNA in the chromosomes, if not that much of it is located inside the mitochondria. This mitochondrial DNA is particularly vulnerable to damage by free radicals because it is closely related to oxidative reactions. Therefore, any damage to the DNA will have a serious effect on the proper functioning of cells (reaching even cause mutations).

Another theory we know today, is the theory developed by Bürger, in that he established that there is a relationship of free radicals in the formation of inter-and intramolecular junctions (cross-links) to the DNA and collagen, resulting the formation less permeable membranes, thus hindering nutritional level exchanges of organs and tissues.

Other authors related the autoimmune reactions with the formation of these crosslinks because  deteriorate the immune system.

Finally, we know that lipofuscin is a pigment derivative of lipid peroxidation, and is also a sign of cell aging caused by the action of free radicals. Normally, lipofuscin accumulates in differentiated cells and exerts its action on unprotected parts of the epidermis and produced colored spots. Furthermore, atrophy sweat and sebaceous glands causing an obstacle to perspiration and, moreover, produces dry skin. However, lipofuscin not only has an effect on the skin, but also acts on tissues, particularly in the central nervous system.

Moreover, the accumulation of free radicals and also damage cellular function, is related to diseases associated with age such as atherosclerosis, arthritis, muscular dystrophy, cataract, pulmonary dysfunction neurological disorders, immune system decline even cancer.

Today, we have several studies that suggest that the use of antioxidants (such as vitamins A, C, E and carotenoids) reduces the formation and hence the action of these free radicals.

In my opinion, this theory itself does not meet the whys of aging. I think to associate with others to explain the aging process in its entirety.

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