A recent medical study compared subjects spending the same amount of time in front of a computer: one group did so with relatively few interruptions, the other splitting the time into smaller segments. Those who spent long periods seated at the computer had a worse record for heart conditions, etc.
And today another study in the news, comparing sitting with standing. Needless to say, you're better off standing. (Winston Churchill, he of the cigars, brandy, and 90-year lifespan, is the poster boy for standing — he wrote all his many books standing, and pacing, at a lectern.)
So if you're inclined to hunker down on a font (or whatever) for many hours at a time, beware.
I can also add my personal experience. I always thought I was pretty fit—worked out regularly, ate sensibly, good body/mass index. But last year I had a coronary problem (thankfully fixed with a stent), which I now attribute to all those dusk-to-dawn sessions at the computer.
So my advice, take lots of breaks. And get your 8 hours sleep.

