Ahoy There Matey:
One fact that contributes to cruising sailors being generally healthy
is that they're doing what they love=less stress. Of course 12' waves
certainly do raise stressg, but it's got a real cause and doesn't
last.......though it seems like it will at the time. By comparison,
the low-level/chronic stress of a job/co-worker/boss you don't like
weakens the whole immune system.

Then too, there's the exercise factor. It's not a 26 mile marathon,
but rather small constant amounts of exercise. I've almost never met
an overweight sailor. (Can't claim the same for
powerboaterssnicker.)
Allan (7 years living aboard, now in medical field.)