ILLNESS can strike us down at any time.
But you may be surprised to learn some are actually more likely to hit at different times of the day.
Experts say that our immune responses are controlled by circadian rhythm – which is basically the body’s 24-hour internal clock.
It runs in the background, regulating between sleepiness and alertness at regular intervals, known as the sleep/wake cycle.
Researchers in Switzerland analysed studies, mainly in mice, and found that adaptive immune responses – are under circadian control.
They discovered that four different conditions were more prevalent at certain times of day: heart attacks, pneumonia, parasitic infections and asthma attacks.
Heart attacks: Morning
The findings, published in journal Trends in Immunology, showed that heart attacks are more common in the morning – and they tend to be more severe than at night.
They noticed that the number of white blood cells that fight off bacteria, viruses and fungi, are elevated during the day.
At night, they are elevated in dead heart tissue – which means there isn’t as much cardiac protection at that time compared with the morning.
Researchers found a bacterial toxin tied to pneumonia initiates an inflammatory response in the lungs of mice.
They noticed that the recruitment of immune cells when the lungs are inflamed showed a circadian pattern.
Separately, more white blood cells can be recruited into the peritoneal cavity, spleen, and liver in the afternoon, therefore resulting in enhanced bacterial clearance at that time.
Parasitic infection: Evening
The findings showed that parasite infections were also time-of-day dependent.
Studies on mice infected with the gastrointestinal parasite Trichuris muris in the morning have been able to kill worms significantly faster than mice infected in the evening.
Allergic symptoms follow a time-of-day rhythm, which is generally worse between midnight and early morning.
The experts say that they also found airway inflammation in mice.
Which they say could relate to a higher risk of asthma attacks during the night.
Senior author Christoph Scheiermann, an immunologist at the University of Geneva, described the findings as “striking”, and added they they “should have relevance for clinical applications, from transplants to vaccinations.”
In both humans and mice, they noticed the numbers of white blood cells also swing back and forth in a circadian manner.
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Scheiermann said it raises the question of whether it might be possible to one day to optimise immune response through awareness and utilisation of the circadian clock.
He added: “Investigating circadian rhythms in innate and adaptive immunity is a great tool to generally understand the physiological interplay and time-dependent succession of events in generating immune responses.
“The challenge lies in how to channel our growing mechanistic understanding of circadian immunology into time-tailored therapies for human patients.”
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