I have to flop back and forth. I work a schedule that requires it - 7 days working 7AM to 7PM, 7 days off, 7 nights of 7PM to 7AM, then 7 off, repeat ad infinitum. The only saving grace of the schedule is that I have a week to transition between days and nights, but it's still difficult. The result is that I can be a night owl or morning bird as necessary, but I prefer being a night owl. Nothing happens at 6AM that I need to know about or be involved in.
I've noticed no health problems so far. I can still pass my flight physical, with no restrictions even for vision, and I've been eligible for Medicare for awhile.