There seems to be no question that being healthy helps you to be happy. More controversial are the reverse claims: that a positive outlook can impact your physical health. An article in POSITIVE PSYCHOLOGY NEWS, Bad Science or New Frontier? The Debate on Positive Psychology for Health, examines the issue. For me, the upshot of the story is that the healing / prophylactic powers of positive psychology haven't been proven definitively, and need a lot more study before they can be made responsibly.
What do you think?