The virtues of a good night’s sleep just got better, with the arrival of the news that the immune system functions best during the night.  Researchers at Stanford University used fruit flies to test their theory but there is strong evidence that the effect carries through to humans as well.

The research team infected the flies with two strains of bacteria, with some flies getting the bacterial infection during the day and others during the night.  Those getting sick during the night were more likely to survive the infection than those getting sick during the day.

Mimi Shirasu-Hiza says her team’s findings suggest we enjoy strongest immunity at night, when other bodily functions have been put to rest.  The Stanford study was presented on Sunday at the annual meeting of the American Society for Cell Biology in San Francisco.

Testing the influence of circadian rhythms, the body’s natural cycle of sleep and wakefulness, flies with impaired circadian rhythms were infected with the same bacteria the other flies were.  Like the flies infected during the day, those with impaired circadian rhythms had a harder time fighting off infection, confirming previous research that indicated bacterial infections hinder the flies’ natural circadian rhythms.

The human body is regulated by circadian rhythms, just as the flies are.  It’s this internal clock that makes us want to eat, sleep, and work at the same times every day and makes us feel out of sorts when our natural sleep cycle is interrupted.