A latest research conducted by Stanford University reveals that the immune system is more active at night provided the person gets a good sleep.

Research was conducted with fruit flies. In the experiment, the researchers infected the flies with two different bacteria at different times of day and night. It was noticed that the fruit flies infected at night were more likely to survive than those infected during the day. 

The aim of the research was to find a link between innate immunity and circadian rhythm. It was found that the fruit flies sick with bacteria lost their circadian rhythm, which means that they were more susceptible to infection. Low "phagocytic" activity was found in the body's innate immune response -- in flies with a corrupt circadian clock.

The study reveals an important fact that the immune system fights invading bacteria the hardest at night and the least during the day.

"These results suggest that immunity is stronger at night, consistent with the hypothesis that circadian proteins upregulate restorative functions such as specific immune responses during sleep, when animals are not engaged in metabolically costly activities," Stanford researcher Mimi Shirasu-Hiza said in a news release issued by the conference organizers.