There are a number of physical, psychological and social changes that occur with the passage of time. Aging, then, can be understood as the impact of time on our bodies. This happens on multiple levels, such as cellular and hormonal aging, accumulated damage, and metabolic aging. Well-being in late life depends on a tightknit balance of physical, psychological, and social health . If one of these three key components of a balanced life style is disrupted, it throws off the other two. For example, if an elderly individual suffers from flu, that in turn, will affect other aspects of their life. This individual may find it hard to be active when ill, which may lead to negative changes in their mood. In addition, other people may avoid him or her due to fear of catching their illness. This could lead to feelings of depression and social isolation, which may further impair immune system functioning.