Defining Types of Causation

Clearly there is a relationship between obesity and lack of exercise and poor diet.  In addition, most philosophers throughout the history of the world have agreed that happiness will, at some point, require meaningful relationships with other human beings.  However, what is not clear about your examples is the difference between causally dependent and causally necessary.  Your definitions almost seem as though these two concepts are interchangeable.  On your view, is causal dependence the same as causally necessary?  Why/why not?