The only health risks of working at nights, or changing hours of work, are in how you feel from day to day. If your body is adjusted to one sleep-and-awake schedule and you force it into another, you can suffer fatigue, poor concentration, insomnia, and at worst depression. There are no long-term health risks. The best remedy is to change all of your routines (meals, exercise, sleep) to the new work schedule, even if it is at night. You should avoid sunlight exposure during the time you should be sleeping and naps when you should be awake.