Since the time of the ancient Greeks, doctors and philosophers have argued whether ageing is a disease or a natural process. Many authors of the Hippocratic Corpus argued that growing old invariably leads to frailty, disability and death, hence they saw ageing as a progressive and incurable disease. But the Roman physician Galen argued that while diseases are abnormal, ageing is universal, so ageing is a natural process rather than a disease. This dichotomy persists to this day and frames our conceptions of the problems of ageing and our proposed solutions.
Unlike Galen and Hippocrates, modern scientists understand how some of the biological mechanisms that cause ageing work. One of these, cellular senescence, sheds important light on the ancient dichotomy.
When cells enter senescence (become old), they release a range of inflammatory factors and enzymes that break down the tissue in which they reside. This lets immune cells reach the senescent cells and kill them. But if this process fails, senescent cells accumulate, changing the tissues in which they reside, causing many of the degenerative changes we perceive as ageing and age-related disease.
Cellular senescence is common across the tissues of the body and happens throughout life. When senescent cells build up in the skin causing wrinkles it is considered a “natural change”. Yet when senescent cells build up in the heart and blood vessels, causing blood vessels to calcify, we call it “cardiovascular disease”. This is an error of logic and categorisation and not due to the intrinsic nature or complexity of pathology or disease.