Current research estimates that the proportion of the population aged 75 and older in developed countries will increase to approximately 40 percent by 2050 [1]. This is the result of the full provision of public health, improved medical care, and adequate nutrition. People have shown a remarkable increase in median life expectancy and, in fully developed countries, life expectancy now approaches 80 years [2]. On the other hand, no matter how much the maximum survival (life span) may be prolonged, the span will not exceed 125 years, as no one has surpassed 122 years and five months (the age of Jeanne Calment in France when she died [3]). Although it has been estimated that if cancer and atherosclerosis were eliminated as causes of death, about ten years would be added to the average life span, there would still be no change in the maximum life span [4]. This may indicate that the current life span of humans has reached its plateau.

Aging is not itself a disease, but it accompanies the decline of organ and body functions and indicates a correspondingly increasing susceptibility to diseases such as infection, autoimmunity, and cancer [3]. Recent estimates from the Surveillance, Epidemiology, and End Results (SEER) Program of the National Cancer Institute reveal that the median age of patients with cancer in the United States is around 70, and that death rates from cancer, for almost any site, increase with each additional decade of age [5].