Just as science is showing that stress accelerates aging, I believe that one day soon science will show that a positive attitude in life produces tangible, physical benefits. This is another one of those things that most people would intuitively guess, but seeing the empirical proof is always of value.
I think science will show that a positive attitude affects the body at a cellular level, just like stress. And this means a positive attitude can literally affect everything about the body, including the internal organs, skin, hair, etc.
But why wait until the proof comes in? Due to the information overload of modern times, it's too easy to get caught in "paralysis by analysis." I know I've fallen in that trap myself. Lately, I've tried to "tune out" a lot of information and listen to my natural instincts more.
The idea that having a positive attitude is good for you, both mentally and physically, is just plain obvious. There are many things that are good for us that won't be "proven" during our lifetimes, but that doesn't mean they shouldn't be tried and implemented.