How susceptible we are to an infection — or how far it progresses — may have something to do with the time of day we're introduced to it. At least that's the premise of a new study from researchers at the University of Cambridge.
To test whether circadian rhythm or biological clock affected infection, researchers infected laboratory mice with herpes viruses at different times of day. They found that in mice infected with the virus in the morning, the virus replicated 10 times greater than it did in mice infected later in the day. The researchers controlled the environment where the mice lived so they routinely had 12 hours of light and 12 hours of dark.
The difference in the rodents' response to virus replication may be due to circadian rhythm, which controls our sleep patterns and body temperature, as well as aspects of our immune systems, according to the researchers. The researchers also repeated the experiment with mice that lacked a gene linked to circadian rhythm and found that their viral replication was high, no matter what time the mice were infected.
“The time of day of infection can have a major influence on how susceptible we are to the disease, or at least on the viral replication, meaning that infection at the wrong time of day could cause a much more severe acute infection,” Akhilesh Reddy, a neuroscientist at the University of Cambridge in England and the senior author of the study, said in a statement. “This is consistent with recent studies which have shown that the time of day that the influenza vaccine is administered can influence how effectively it works.”
The findings from the study, published in the Proceedings of the National Academy of Sciences, may help explain why shift workers, whose body clocks are often regularly disturbed, are more likely to have health problems than people who stick to regular wake and sleep schedules. However, it's not clear if the mice-only study will translate to humans.