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Circadian Colds

September 19, 2014

Why do the symptoms of common respiratory infections often worsen at night?



Cyclical symptoms. I’m Bob Hirshon and this is Science Update.

Many people suffering from viral infections notice a dramatic worsening of their symptoms in the evening. We asked Vanderbilt University infectious disease specialist William Schaffner about it.

WILLIAM SCHAFFNER (Vanderbilt University):

Come 4 o’clock in the afternoon, all of a sudden their energy lags, their temperature may actually go up a degree or two, and they feel kind of punky again, and this can extend through much of the evening.


He says our circadian rhythm, or cyclical body clock, is responsible for the evening blahs. Most infections accentuate the normal circadian cycle, leading to metabolic and hormonal changes that raise body temperature and boost inflammation, often making us feel worse at night. Not everyone has this experience of course. But Schaffner says doctors who routinely make their hospital rounds in the early morning can sometimes miss the severity of a patient’s symptoms due to the time of day. I’m Bob Hirshon, for AAAS, the science society.