Our medicines prevent many diseases from killing us. Advances in medical science have allowed us to fix damaged organs, like hearts, or in some cases replace them entirely. The further understanding of nutrition provides us with the knowledge we need to stay healthy throughout our lives. But despite all this, there is still no way to defy death permanently. We can prolong life, almost tripling its natural length, but eventually, the human body can no longer support itself.
So why does this happen? Whilst the precise cause of ageing is as of yet undetermined, there are many theories. One theory indicates that the mitochondria, which are the energy production units in our cells, cause damage to the cells over time via the release of harmful by-products. Mitochondria produce ATP (the energy currency of the cell) through several cycles that split glucose down into various compounds, releasing energy in the form of ATP along the way. This process can release electrons which form reactive oxygen species. You may be more familiar with these under the guise of free radicals. These molecules cause damage to several different components of the cell. Over time, this cell damage builds up, and we see the effects of this in the form of ageing.
Another theory is more centred around DNA as the cause of ageing. As you may know, DNA (or Deoxyribonucleic Acid to be precise) is found in every cell in our body and contains the instructions for each one of the cells. The DNA in our cells produce protein, which activate different functions around the body. When a cell divides, a copy of the DNA is made, after which the cell divides in two. The process of replication is balanced by the rate of cell death. In the first part of our lives, as we grow, the rate of cell division is higher than that of the rate of cell death. However, at about 25 years of age, the rate of cell division begins to decline. It is at this point where our bodies start "ageing" as we know it. This decline in division is the result of the degradation of telomeres. These little caps of DNA are fascinating, and I'll be taking a closer look at them in a future posts.
One final theory around ageing implicates insulin as a contributing factor. You probably already know of insulin through its role in diabetes, but studies have shown that it could also cause ageing when combined with a chemical referred to as insulin-like growth factor 1, or IGF-1. IGF-1 can bind to both specific receptors as well as insulin receptors. Many tests have been conducted on a variety of different species that indicate removal of insulin receptors can lead to incredible prolonging in life. An experiment showed that the lifespan of the roundworm species Caenorhabditis elegans could be doubled by mutating the gene that coded for the insulin-like receptor. Since the insulin/IGF-1 pathway is the same within both worms and mammals, this indicates a possible anti-ageing therapy that could extend life permanently.
It's difficult to say exactly if any of these are the one true cause of ageing. It could be that it is a combination of all the different theories, or it could be that one theory in turn stimulates the others. Whatever the case, each theory offers exciting avenues for potential therapies in anti-ageing.
An excellent review on insulin/IGF-1 ageing theories can be found here; http://www.fly-bay.net/journals/cc/BartkeCC7-21.pdf