Immune System Works Better at Night

Greater success fighting infection than during the day, study says.

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MONDAY, Dec. 15 (HealthDay News) -- A good night's sleep really does a sick body good, new research says.

Stanford University research with fruit flies reveals that the immune system fights invading bacteria the hardest at night and the least during the day. The findings were to be presented Sunday at the American Society for Cell Biology annual meeting, in San Francisco.

"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.

Circadian rhythm paces the human body as well as the fruit fly, running internal clock's time for eating and rest every day.

The researchers noted that previous experiments with flies found that bacterial infection threw off the insects' circadian rhythm, and not having this internal clock working properly made them highly susceptible to infection.

In this experiment, the researchers infected the flies with two different bacteria at different times of day or night. Those infected at night were more likely to survive than those infected during the day. The researchers also detected low "phagocytic" activity -- the body's innate immune response -- in flies with a corrupt circadian clock.

More information

The National Sleep Foundation has more about how sleep works.

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