Which headline is more likely to grab your attention?
‘Viruses ‘more dangerous in the morning”
‘Sleep cycle time of infection affects the growth of viruses in mice and cells’
Even as a scientist I’m more likely to follow a link from the first line. Snappy headlines do an important job, they capture our interest, but they don’t always give us the full story. This is the start of a regular post looking at the science behind an some of the eye catching headlines. To be clear, I’m not criticising the science reporting in these pieces. The original article for this week’s headline explains the study it is based on and possible consequences clearly and reasonably. Catchy headlines have their place drawing our attention to interesting research. This is just a chance to take a deeper look at the science surrounding the words of the headline, and a fun check on whether you should be rushing to change your day to day habits. So on to this week’s headline…
Viruses ‘more dangerous in the morning’?
The article is about a recently published study by researchers at the University of Cambridge, looking at the effect of the body clock on viral infections. Our daily cycle of sleeping and waking is controlled by changing levels of chemicals in our body called clock proteins. They set cycles called circadian rhythms which affect when we sleep and wake, as well as other body functions like temperature and response to food and exercise. We’re also beginning to learn they might be important in health and disease, for example by influencing our immune system. Some studies have noticed that some inflammatory diseases tend to be worse at certain times of day, for example rheumatoid arthritis flare ups tend to come in the morning. The levels of chemicals that causes inflammation in the body also go up and down with the sleep cycle, and this can change the response to bacterial infection. These researchers wanted to find out if the something similar might be true for viral infections.
The researchers infected mice with specially labelled bio-luminescent (glowing) viruses at either the beginning or end of their ‘active time’. Mice are nocturnal so we can’t really call it morning and evening, since for mice the day starts when the lights go out. Luckily mice have similar clock proteins and immune systems to humans so they are a good ‘model’ to try to copy what might happen in a human body in a comparable situation. Choosing models for experiments is an interesting issue and I’ll talk more in depth about it another day. Long story short: nothing is perfect, but mice are a favourite with immunologists. After infecting the mice they used the brightness of the glowing viruses to work out how fast they reproduced. They saw that the viruses took hold better in mice infected at the start of their active time, when the levels of a clock protein called Bmal1 were low. To check whether this effect was to do with changes in the immune system or directly to do with the body clock they looked at a model with no immune system. Instead of infecting a mouse they infected cells growing in a dish. They saw the same patterns, the viruses grew better at the start of the active time. This means that the difference is probably linked to cell and clock function rather than changes in the immune system. Viruses rely on hijacking the cell’s machinery to be able to grow. Infections started later in the day when the body is starting to wind down might be trying to use machines that have already been switched off. So does this really mean that viruses are more dangerous in the morning?
One slight hitch is that the experiments don’t actually look at how dangerous the virus is, they don’t measure the health of the mice, just how fast the virus is growing. A big dose of virus at the start of an infection could actually kick start a better immune response later down the line, as the researchers point out in their conclusion. Another complication is that the mice and cells from these experiments have pretty strict bed times, their circadian rhythms are set up to be perfect examples for an experiment. Humans are less disciplined, we turn on the lights when it’s dark outside, we stay up late and some of us even work all night (shift workers, stressed out PhD students….). This can mess with our clock proteins. Interestingly shift workers tend to have lower levels of the clock protein Bmal1, which based on these experiments could allow viruses to grow faster.
Let’s assume for a second that after lots of follow up research we find out viruses are more vicious at sunrise, what would it mean for us? It could change the advice for behaviour during pandemics, we might ask people to stay away from each other during the day when infections could be worse. Shift workers with altered body clocks could be offered flu vaccines to help combat their virus risk. It might even change when we give medicines. Trials giving elderly patients vaccines in the morning have already shown some promising results. Understanding how the body clock affects disease and immune function could help us treat and prevent illness more effectively. Experiments like this are a step in the right direction. But unfortunately I don’t think we can use the next cold outbreak as an excuse to hide in bed until lunchtime quite yet.