It is common to hear that we all age and that aging is a natural and even inevitable process, that it is a physiological process intrinsically linked to the human (and animal) condition. However, to what extent is this statement fully accurate? In the late 2000s, scientists came up with a tentative hypothesis for the causes, or hallmarks, of aging. These hallmarks are arranged into a “pizza”, whereby each hallmark represents a slice which has an equal weighting, as seen in the image below.
 Aging Hallmarks
So, according to López-Otin et al , the nine conjectural hallmarks of aging, in different organisms, are: genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient-sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication.
Notwithstanding, more recently, Dr. David Sinclair, Professor of Genetics at Harvard Medical School, one of Time´s most influential figure and a prominent figure in the field of research related to aging, argues that there is one hallmark of aging which predominates over the others: epigenetic alterations. That is, aging is a loss of epigenetic information, which are the control systems which regulate which genes are expressed and which ones are supressed at a certain time in a cell.
Additionally, Dr. Sinclair claims that the other hallmarks of aging, mentioned above, are largely manifestations of this major hallmark (epigenetic alterations). Thus, we will now talk about some of the main causes of epigenetic alterations in the human genome which contribute to and accelerate aging.
Smoking is one of the main causes of epigenetic instability, as it exhausts the DNA repair systems which are recruited due to the DNA damage induced by smoking. Other major causes of epigenetic alterations include: N-nitroso compounds, which are found in many red meats and bacon (these compounds are powerful carcinogens) and exposure to radiation (including X-rays and gamma rays). In other words, the environment (that is, exposure to radiation and different forms of toxicity) and lifestyle (namely diet, exercise and stress), in all its dimensions, both contribute to a greater amount of epigenetic alterations, which in turn intensify the aging process.
To conclude, there are nine major hallmarks which underpin the aging process. However, the key hallmark which appears to trigger the other hallmarks is epigenetic alterations. In the next articles, we will elaborate on the topic of epigenetic alterations, the factors that accelerate it and how to minimise its impacts.