The body's immune system works hardest at night to fight off bacteria and eases off during the day, according to a new study done on fruit flies.

Researchers found that flies infected with bacteria at night had a better chance of surviving than did the flies infected during the day.

The result fits a theory that the body uses sleep to give more energy to restoring the body, said researcher Mimi Shirasu-Hiza of Stanford University.

Circadian rhythms pace the human body as well as the fruit fly through its days and nights, setting the rest/activity cycle that cues when to eat, sleep and mate over a 24-hour cycle, according to a news release.

The work looked at phagocytosis, when immune cells engulf and destroy the bacteria invading the body. In people, immune responses such as phagocytosis clear bacterial infections but also may be a part of some diseases, including cancer and disorders such as Alzheimer's.

The findings will be presented to the American Society for Cell Biology this week.