Proposing a Staging System for Aging
One logical outcome of a growing ability to treat aging as a medical condition, with therapies that target the underlying causes of aging such as senescent cell accumulation, is that aging will be staged. A patient will be assessed and declared to have stage I aging, or stage III aging, as determined by some combination of factors. The medical community assigns stages to many chronic conditions, an assessment of severity and progression that is used to decide upon treatment strategies. Like those chronic conditions, aging as a whole is the consequence of underlying processes of damage, and has a clear progression. In the paper here, the authors argue that the time has come to set up a staging system for degenerative aging.
In the coming decades, the proportion of older adults in the world will nearly double. Older adults are a heterogeneous population, with many people over the age of 80 continuing to work and travel, while others might be weak, chronically ill, or disabled. A traditional framework for describing different populations of older adults is "young-old," "old," "old-old," and/or "oldest old". Fried's frailty phenotype is a similar three-stage framework in which people are classified as non-frail, prefrail, or frail. Proteomic analysis finds large changes in gene expression at about the age of 40, 60, and 80. However, these frameworks are not adequate to describe the different stages of aging and subpopulations of older adults. Older age is a risk factor not only for normative physiological changes with aging but also for cancer, heart disease, diabetes, dementia, and many other chronic conditions. Genes, disease, and behaviors can pull on the chronological age of a person and make the person appear younger or older with the risk profile ("biological age") of someone younger or older.
Aging can be viewed as a very slow step-wise decline from wellness and independence toward disability, reduced quality of life, and ultimately death. The rhythm of decline of an individual is very personal and depends on the genes, lifestyle, diseases, and geriatric syndromes such as dementia and falls. The biological causes for physiological changes with aging and for the prevalence of age-associated diseases continue to be explored and debated. Dividing the process of aging into phases, and characterization of these phases from various aspects can raise awareness and recognition that old age is not homogeneous or stereotypical as it is often considered. Healthy, active people in their 70's should not be treated like disabled people in their 90's, and active people in their 90's should not be treated like sick, disabled people in their 90's.
Adults in stages one and two of aging (age 60-79) typically remain in the first stage of the four-phase functional scale. The rate of decline to the next phases depends on vascular risk factors, genetics (family history), and social/environmental factors (such as education, career, physical activity, and social engagement or isolation). The goal of medicine is to compress morbidity, allowing old and old-old adults to spend more time in these earlier functional aging phases and less time in the disabled or burdened phase with bothersome symptoms.
Chronological age stratifications may not correlate with medical, functional, emotional, and social changes that an individual may be experiencing for multiple reasons. The chronological age strata used in this study are obviously inexact, but useful. As noted, older adults are heterogeneous and may develop problems earlier than average or later or never. The final chronological age strata in this proposed staging system are older than 85. In fact, there may be substantial differences between 87-year-olds and centenarians. However, at this time, there is insufficient data to describe organ system changes and disease epidemiology in subpopulations like centenarians. With the advancement of modern medicine and with improved preventive care and lower rates of infectious disease, we more often witness an expanding gap between chronological age and biological age. Some people with advanced age have functional and cognitive abilities that are greater than those of younger people.
Nice paper. I would have better developed a stratification with aging biomarkers. There are only touched in references 44 and 45 mentioning the lack of clinical use and possible misinterpretation.