I used to commute 72-75 miles a day, that was too much, all i did was eat sleep cycle or work. Moved closer to work and now do 31-35 miles a day and that's much more sensible!
Most important thing is sleep, any less than 8 hours a night and I feel it on the bike, other thing is food, eat plenty of good food, particularly at work, don't just rely on a sandwich, it won't be enough! Also make sure you drink plenty of water, easy to get dehydrated at work if you're not careful.
Another thing to consider is the quality of the bike you're riding.
I've just bought a new Trek FX7.5 Hybrid which has cut my journey time by a good 10 minutes each way, 20 minutes a day. I'm also finding it less tiring. Old bike was a Carrera hybrid, big heavy and far from the greatest but did a job and clocked up about 6000 miles on it before it started completely falling to bits
. This week though, first week on the new bike and really wishing I'd changed a year ago.