What is losing balance a symptom of?

Our balance system depends on many body parts to function normally. Aging alone can affect any one or more of these parts. Balance and mobility disorders are the most prevalent limitation in activities of daily living of seniors, affecting nearly 40 percent of those over age 80. A few of the contributors to poor balance at any age include:
•    History of stroke or brain disease
•    Abnormalities of the motion detectors in our inner ear
•    Impaired vision
•    Loss of nerve sensitivity in feet 
•    Arthritis affecting joints in the legs or feet
•    A medication side effect