Well, pretty much what Moosebunk said, shiftwork is not good for the body period..unless you're a Zombie or Vampire. It can be done when you're young, much past the mid 30's and it really wreaks hell on the body. You (your body) doesn't know when to relax, poop at the right time of day, is it sun up or sun down. I worked different shifts from 18-51 and the last 7 years straight days with the odd afternoon shift. Waaay better.
Worked 9/6, 3 afternoons, 3 nights, 3 days( 8hr) and 6 off. Worked 2 days, 2 nights(12 hrs) and 4 off. Then a wierd 2 afternoons, 2 days, and 2 nights(8 hr) short change(only 8 hrs off between the shift rotations. Finally the 3days/2nights, off 5, 2 nights, 3days off 5 and 2days, 2 nights 4 off. Off 2 weekends a month and work 2.