The problem with night workers that they have unstable sleep schedule. Even if you work at night, you still have cope with some things daytime, hence often breaking of circadian rhytms. The more irregular the sleeping schedule is, the more is health risk (The most dangerous work schedule is rotating shifts). If you are consistent in your sleeping habits, health risk lowers. But as I pointed out it is not possible in today's social setting to be a 100% night person, therefore the observation of health problems in night workers.
I have a stable schedule and don't consider having bad sleeping habits - going to sleep at 4am, getting up at 12pm when I don't have uni. I used to set myself a goal of having a 'normal' sleeping time (11pm - 7am), but after a time it goes back to 4am - 12pm, with 11pm - 1am being the peak of activity.