Biomarkers of aging - current state of knowledge.

Aging is a process of gradual decline in the functional capacity of the human body that leads to a significant increase in the risk of death over time. Although it is a process universal to all animals, its rate is not the same. Biomarkers of aging aim to better describe the aging process at the level of the individual, organ, tissue, or single cell. They are used to estimate the rate of aging and predict the probability of death. They are good indication of the current state of the organism and are more accurate in predicting a person's susceptibility to disease, its progression and the likelihood of complications and death. Simple biomarkers measure only one parameter or a narrow group of related parameters that have a known association with age, in human or in a laboratory model. They can be divided into molecular (based on features of aging), functional (describing decreasing functional capacity during aging) and anthropometric (describing structural changes). Composite biomarkers are the most comprehensive way of measuring biological age. They combine a large amount of data, which they evaluate using algorithms often based on artificial intelligence. The most widely used method for measuring biological age in composite biomarkers is the epigenetic clock. The aim of this article is to review the many existing markers of aging and describe their relationship to aging.