Easy way of gaining or losing five years of life
books.google.com
books.google.com
Teorically if you slept only 5 hours a day, you would live 5 years more in wake time during your lives, but... perhaps there should be studies correlating sleep deprivation and a shortest live span.
Nonetheless that is an interesting theory if we combine it with polyphasic sleep, which could ease the effects of sleep deprivation.
But then I also find information saying that it really varies from person to person, and that it's best to make sure that you don't feel tired during the day; if so you're probably okay.
(Note that this is all second hand. I've never really sat down to read studies themselves, I just read journalist interpretations.)
Anecdotally, I've had little problem with my sleep schedule. It gives me an extra chunk of time in the morning which I find extremely helpful, and I rarely find myself worn out until a little before I normally go to sleep.