When the immune system naps

Time of day affects the body's ability to fight germs.

Gregory Nemec

Gregory Nemec

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Your body may be better able to fight germs at certain times of the day, new research by Yale professor Erol Fikrig and colleagues shows. Their study suggests that components of our immune system are under the control of circadian rhythm, the 24-hour cycle of waking and sleeping. If that cycle is disrupted, we may be more susceptible to illness.

The study, published in February in the journal Immunity, used mice to test whether a certain gene that enables the body to recognize bacteria and viruses (in the form of either a vaccine or a pathogen) functions differently during the day and night. The answer was yes.

Fikrig’s team found that the mice responded better to vaccines at night, when they are active, than during the day, when they sleep. When the researchers investigated further, they found that in mice, the circadian clock regulates the activity of a gene called TLR-9, which has a major role in driving the ability of white blood cells and other immune-system cells to recognize viruses and bacteria. The study’s main finding, says Fikrig, is that the “immune system is not functioning the same all day long.” When he conducts research on humans, Fikrig expects to find that the genes function at their highest level during the day and at their lowest level at night. The biological reason for this, he speculates, is that people are out and about more during the day and exposed to more pathogens. 

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