A new study in Mechanisms of Ageing and Development on March 9, 2020, describes how aging fits the criteria for a disease under the International Classification of Disease.
Aging meets World Health Organisation (WHO) criteria used for classifying conditions as diseases, according to a team of scientists from the International Longevity Alliance, the Biogerontology Research Foundation, and the Department of Risk Factor Prevention.
An international team of gerontologists, or scientists who study aging, analysed how the aging process compared to criteria found in the International Classification of Diseases (ICD-11), a reference developed by the WHO to help doctors and other healthcare professionals identify diseases. They concluded that features common to aging, such as low-grade systemic (whole body) inflammation, the decrease in cellular division, and hormonal changes, among others, fits the ICD-11 criteria for being considered a disease.
Aging can be defined as a progressive functional decline in the body, leading to individuals’ reduced ability to adapt to the environment. These functional declines include physiological and mental changes. Whether these changes constitute a disease, however, remains an open debate within the scientific community. The World Health Organization defines a disease as a set of dysfunctions that adhere to the following characteristics: a set of dysfunctions in any part of the body that follows patterns of symptoms, can be explained by an underlying mechanism, develops over time, responds to medical interventions and can be linked to genetic and environmental factors.
The scientists thought that biomarkers of aging provide evidence of aging having a set of signs and symptoms. A number of blood-based biomarkers, including markers of inflammation, matched the ICD-11 criteria for disease. They found measurements of physical function, such as walking speed, balance, grip strength, and muscle mass, matched the criteria used to define disease. Certain measures of frailty, such as unintentional weight loss, self-reported exhaustion, weakness, slow walking speed and low physical activity also met these criteria. Finally, genetic biomarkers of aging met disease criteria, such as the decay of telomeres: specialized sections of DNA at the ends of chromosomes that protect against DNA damage during cellular replication. The scientists thought these biomarkers provided evidence of aging having a set of signs and symptoms.
The authors of the review argue that several disease-like cellular and physiological mechanisms underlie the aging process. At the cellular level, these mechanisms include chronic low-grade inflammation and replicative senescence, or the inability of cells to divide and proliferate as they age. Aging-related body composition changes reflect a mechanism of aging whereby the body undergoes changes to contain more fat as compared to lean body mass.
This image indicates all of the ways mechanisms of aging interact with one another. Dotted lines reflect relationships for some organs only, and solid lines mark relationships relevant in the human body in general. (Aging fits the disease criteria of the International Classification of Diseases | Mechanisms of Ageing and Development)
How an illness progresses and resolves, its course and outcome, respectively, are key metrics used to classify disease. The team determined that the course and outcome of aging once again fit the ICD-11 disease criteria. The course of aging is chronic, and age-related diseases do not typically vanish over time. In the absence of any other age-related diseases, aging will always result in death. This adds credulity to aging-related diseases not entirely explaining the pathological effects of aging.
A number of responses to interventions also exist for aging. The most noteworthy interventions listed in the study include exercise and a healthy diet. The authors list healthy diets high in flavonoids, olive oil, coffee, nuts, legumes, whole grain products, and magnesium as potential interventions.
As many diseases are genetic in nature, the ICD-11 includes genetic criteria for determining whether a condition may be a disease. Gene variants associate consistently with longevity, although to date, only a few have been identified. Epigenetic changes, which alter the activity of genes without changing the DNA code, play an important role in aging as well. Our understanding of how epigenetic changes influence aging, however, remains incomplete.
The last part of the ICD-11 definition of disease is linkage to interacting environmental factors. Environmental factors influencing age-related outcomes include smoking, alcohol intake, and physical activity. Modifying these environmental influences could improve healthspan during aging.
The authors conclude that “[H]uman aging can be described in terms of the WHO criteria for disease.” Importantly, treating aging like a disease will change how medicines to treat it are funded, developed and approved.