People are more vulnerable to infections during the day, suggests a new study conducted by researchers at the University of Cambridge. The body clock affected the ability of viruses to replicate and spread between cells, with those in a resting phase or with a disrupted body clock more likely to succumb to illness.
The finding may help explain why shift workers, whose body clocks are routinely disrupted, are more prone to health problems, including infections and chronic disease.
‘Body clock affects the ability of viruses to spread between cells. Shift workers have a disrupted body clock and they are more susceptible to viral infections.’
When a virus enters the host, it hijacks the host cells to replicate and spread. The resources of cells fluctuate through the day in response to the circadian rhythm which controls the functions during sleep patterns, body temperature, immune system and the release of hormones.
A study was conducted in mice infected with herpes at different times of the day, with scientists measuring the levels of virus infection. The mice lived 12 hours in daylight and 12 hours in dark under a controlled environment.
The researchers found that virus replication in mice infected at the very start of the day was 10 times greater than in mice infected 10 hours into the day, when they were transitioning to their active phase.
The researchers focused on one body clock gene called Bmal1, which has its peak activity in the afternoon in both mice and people. The researchers found high levels of virus replication regardless of the time of infection.
The research was conducted at the Wellcome Trust - Medical Research Council Institute of Metabolic Science at the University of Cambridge. "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," said Professor Akhilesh Reddy, the study's senior author. "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."
When the body clock is disrupted, the timing of infection no longer mattered as the viral replication was always high.
Dr Rachel Edgar, the first author, said, "This indicates that shift workers, who work some nights and rest some nights and so have a disrupted body clock, will be more susceptible to viral diseases. If so, then they could be prime candidates for receiving the annual flu vaccines."
Genes that control the body clock undergo seasonal variation. They are less active during the winter seasons, when influenzas are more likely to spread through populations.
The study is published in the Proceedings of The National Academy of Sciences.