The common cold is the also-ran of infections. ‘It’s just a cold’, is what we tend to say. No big deal.

Consider this from a Conversation piece published in September:

• On average, children have four to six colds per year, while in adults the average is two to three
• The usual cold persists about one week, although 25 per cent last two weeks. In one study with 346 adults, the infection lasted 9.5 to 11 days
• A cough tends to last longer than other symptoms, and often beyond the actual viral infection. The average duration of a cough is about 17.8 days.

Taken together, that’s a lot of time blowing your nose, talking through your tonsils and glueing your face to the pillow.

So what can we do to lower the number of colds we develop, and with that, the number of days feeling crook?

Sleep and the common cold

For years it was taken as “mother’s wisdom” that poor sleep put you at risk of a cold. Nice idea, but is there anything to it?

Surely, you might argue, colds come from viruses, and if you’re exposed – on the train, at the supermarket – you’re bound to feel unwell in a few days. No?

Not necessarily. Our immune system can successfully neutralise an infection.

Turning that around, a lack of sleep punishes the immune system and puts you at greater risk of developing a cold.

Who says so? Not just mummy

A couple of well-designed studies have demonstrated that adequate sleep does in fact protect people from infection.

A 2015 experiment from the University of California San Francisco found that “sleep-deprived individuals are more than four times more likely to catch a cold than those who are well rested”.

As reported in Science, this was a two-part experiment that began with scientists collecting nightly sleep data on 164 healthy participants for one week.

This involved the participants recording “the times at which they went to bed and woke up”.

Sleep patterns of participants were recorded, they were then infected with rhinovirus.

But they also wore small actigraphy devices, similar to Fitbits, that monitored movement while they slept.

The researchers worked on the assumption that movement recorded during a reported sleep period indicated wakefulness.

People do move about while sleeping to some extent. Nevertheless, the time spent moving was subtracted from the hours recorded as sleep.

Part two: Exposure and quarantine

Before proceeding to the next stage, the participants had their blood taken and were given nasal drops containing either the rhinovirus or a placebo control.

Prior to this administration, the participants were tested for the rhinovirus antibody, the immune agent that attacks the virus.

Those with high pre-existing levels of the antibody were released from the experiment “so that prior immunity would not bias the infection rates of the group”.

High levels might suggest they were already sick.

Quarantined for five days

The participants were then quarantined in a hotel. The entire floor was sealed for five days and the scientists waited to see who became ill. Assessing sickness went beyond counting sneezes and coughs.

Used tissues were collected, snot was weighed. “Ten grams or more were counted as a sign of illness.”

Congestion was measured by dripping “a harmless dye into participants’ noses and waited to see how long it took to reach the back of their throats; longer than 35 minutes tallied as a sign of illness”.

Mucus samples flushed from a participant’s nasal passage were tested for signs of viral replication.

Blood tests were investigated “for new levels of the rhinovirus-fighting antibody”.

The results

Out of the 124 that received the virus instead of the placebo, 48 of the participants became sick.

The sleep duration of these sick participants was checked.

The researchers found that participants who slept fewer than five hours a night were 4.5 times more likely to get sick than those who slept seven hours or more.

Those who slept five to six hours were 4.2 times more likely to get sick.

Those who slept six to seven hours per night were at no greater risk of catching the cold than those who slept seven hours or more, “suggesting that there’s a sleep threshold for potent immune defence”.

Dr Aric Prather, lead author of the study, told Science that the experiment “provides some really clear evidence for those people who get less than five or six hours of sleep there really is a clear biological cost”.