People grow old gradually, and as they age so do their disabilities. The number of disabled elderly is growing rapidly in many countries worldwide. "Disability" is usually defined as restrictions in the capacity to perform activities of daily living (ADL), or in the inability to function independently in terms of basic or instrumental ADL.
According to the World Health Organization, 10 percent of the world's population has some form of disability. Among them, 20 percent of those aged 70 or more and 50 percent of those over 85 are disabled. In the United States, it is estimated that the number of people who will suffer functional disability will increase at least 300 percent by 2049.
Several diseases can affect the elderly. The major chronic conditions are cardiovascular diseases, hypertension, stroke, diabetes, cancer, chronic obstructive pulmonary disease, muscular-skeletal conditions including arthritis and osteoporosis, mental health conditions such as dementia and depression, and blindness and visual impairment. To these conditions should be added injuries due to falls and road traffic accidents.