Physical Aging Aging produces normal physical changes. All of the cells of the body begin to change by becoming more rigid and more brittle. These cellular changes cause changes in vision, hearing, and the circulatory and digestive systems. As physical changes progress, disease becomes more prevalent. As the population ages, more diseases occur, and we do not know the reason why. Experts have looked for ways to determine the difference between the normal physical changes caused by aging and the development of disease. In order to support the effort to differentiate normal aging from disease, professionals have developed three principles of age-related disease development.