Naturally occurring ageing within the human body is a complex natural process that is continuous and progressive, not an accidental and sudden phenomenon. This process is accompanied by a gradual progression of physiological ageing in older persons, with changes in individual morphology and in the composition and functioning of the body's tissues and organs, which, to varying degrees, have far-reaching effects on the quality of life of older persons in their later years, leading to a gradual weakening of their physical and mental functions and an increasing risk of illness and death.