New Delhi, Nov 15 (ANI): Jet lag, shift work or any late night might be the reason behind you getting sick, a new study has revealed. That's because the body's internal clock is set for two 12'hour periods of light and darkness, and when this rhythm is thrown off, so is the immune system. According to the new study, one reason might be that the genes that set the body clock are intimately connected to certain immune cells. The study is published online in the journal Science.