aging

Aging is the gradual decline in physiological function and increased susceptibility to disease that accompanies advancing age. It is not merely the passage of time; chronological age is a calendar measure, while biological age reflects the functional state of tissues and organs. Biological aging varies among individuals and underlies many age-related conditions, including reduced mobility, altered metabolism, and cognitive changes.

At the cellular level, aging involves accumulated DNA damage, telomere shortening, and alterations in gene regulation. Cells can enter senescence or die, contributing to tissue dysfunction. Proteostasis, mitochondrial function, and autophagy decline, while chronic low-grade inflammation, sometimes called inflammaging, persists. Epigenetic changes alter gene expression without changing DNA sequence, affecting tissue homeostasis.

Several theories seek to explain aging. Damage accumulation and failure of repair processes have been proposed, alongside programmed aging and telomere-based limits. The inflammaging framework emphasizes sustained immune activation and metabolic changes that increase disease risk with age.

Aging increases the risk of cardiovascular disease, cancer, neurodegenerative disorders, and frailty, and it often accompanies loss of muscle mass and bone strength. The concept of healthspan aims to describe the portion of life spent in good health rather than in disease. Research seeks biomarkers of aging, such as epigenetic clocks and telomere length, to estimate biological age and study interventions.

Population aging is a demographic trend with implications for healthcare, social security, and caregiving. Public health measures that promote nutrition, physical activity, vaccination, and management of chronic diseases can delay functional decline and extend healthy years.