Tuesday September 1 2015
Having a cold can make you feel miserable
"Sleep longer to lower risk of catching cold," says The Daily Telegraph of research on how sleep duration and quality could affect your risk of catching a cold.
In this small, research experiment, electronic sleep sensors and records of how much volunteers slept were used to determine sleep patterns before the volunteers were given a dose of a common cold virus. Researchers then looked at whether they developed cold symptoms over the following days.
Those who slept less than five hours were four-and-a-half times more likely to catch a cold than those sleeping more than seven hours a night. A similar result was found for those sleeping five to six hours. Those who slept between six and seven hours were at no greater risk of catching a cold.
These findings support the importance of a good night's sleep in terms of health and wellbeing, but it doesn't prove sleep to be the single direct cause of a cold.
Many factors will inevitably determine whether you catch a cold – and although the researchers tried to account for some of these factors they could together be influencing people's susceptibility to the common cold.
Rather than worry about how long you've slept, simply try to keep your hands clean to reduce your chance of getting or spreading common cold viruses.
Where did the story come from?
The study was carried out by researchers from the University of California, Carnegie Mellon University and the University of Pittsburgh Medical Centre. Support for the study was provided by the National Center for Complementary and Alternative Medicine, the National Institute of Allergy and Infectious Diseases, National Institute of Health grants and the National Heart, Lung and Blood Institute.
The study was published in the peer-reviewed journal Sleep.
This has been reported widely and, for the most part, accurately in the UK media. However, the Daily Telegraph's statement that "lack of sleep is the most important factor in determining whether someone will catch a cold" gives a misleading impression of the findings of this controlled experiment. It is likely that exposure to the cold viruses and lack of good hand hygiene are the most important factors in the spread of cold, but these were not examined in this study. Its headline assumption that you should "sleep longer to lower risk of catching cold" is also not necessarily supported by this evidence.
What kind of research was this?
This is a prospective study that looked at whether shorter sleep duration and interrupted sleep could predict susceptibility to the common cold. The study involved monitoring the sleeping habits of healthy, infection-free volunteers for a week before giving them nasal drops containing a common cold virus (rhinovirus 39). They were then monitored for the development of symptoms of the common cold.
This is a good way of observing how a particular exposure (in this case, sleep quality) may be associated with a subsequent outcome (in this case, the development of a common cold). However, it still can't prove direct cause and effect, as other factors could be involved.
What did the research involve?
Researchers recruited 164 healthy volunteers, comprising 94 men and 70 women aged 18 to 55 years old. Volunteers were excluded if they:
The volunteers were enrolled two months before being given the rhinovirus dose. During that time they completed questionnaires, two weeks of daily interviews to assess emotions, and underwent a week of sleep behaviour monitoring using a combination of wrist actigraphy (by a kind of wrist-worn electronic motion-sensing device called an actiwatch) and sleep diary. Blood samples were taken before and after this two-month period to assess antibody levels.
Sleep measurements were taken using the actiwatch for seven nights. This measured total sleep time, used to estimate sleep duration, and fragmentation index, which is a measure of restlessness during sleep. The volunteers also filled in sleep diaries, reporting the time they went to sleep, what time they woke up and how long it took to fall asleep.
Volunteers were then given a dose of rhinovirus via a nasal dropper. They were considered to have a cold if they were infected and met illness criteria. To be infected, their virus-specific antibodies must have increased at least fourfold. Illness criteria were either:
- a total adjusted mucus weight of 10 or more grams (assessed by collecting and weighing all their used tissues)
- a total adjusted nasal clearance time of 35 minutes or longer (assessed by administering a coloured dye to the nasal passage)
The researchers looked for the association between sleep quality and the common cold, taking into account potential confounding factors, including:
- household income
- season in which trial occurred
- health habits – such as physical activity, smoking, alcohol consumption
- psychological variables – perceived socioeconomic status, perceived stress, positive emotional state
What were the basic results?
Sleep duration was categorised as:
- less than five hours
- five to six hours
- six to seven hours
- more than seven hours
The study found that shorter sleep duration as recorded by the actiwatches was associated with increased risk of developing the common cold.
Participants who were recorded as having less than five hours' sleep had an increase of four-and-a-half times the risk compared with those sleeping more than seven hours a night (odds ratio [OR] 4.5, 95% confidence interval [CI] 1.08 to 18.69). A similar result was found for those sleeping five to six hours a night (OR 4.24, 95% CI 1.08 to 16.71). Those who slept between six and seven hours were at no greater risk (OR 1.66, 95% CI 0.40 to 6.95).
Sleep fragmentation and self-reported sleep durations were not found to be significant predictors of cold susceptibility. These findings remained after adjusting for all measured confounding factors.
How did the researchers interpret the results
The researchers conclude that: "Shorter sleep duration, measured behaviourally using actigraphy prior to viral exposure, was associated with increased susceptibility to the common cold."
This study assessed the effect of sleep duration and fragmentation on common cold susceptibility.
It demonstrated that those who had less than six hours' sleep a night were at increased risk of catching a cold after direct exposure using the nasal dropper, compared with those having more than seven hours a night.
This finding matches previous work suggesting that poor sleep can lead to adverse health outcomes. However, the study cannot prove poor sleep as the single direct cause of susceptibility to infection.
The researchers took care to control for various possible confounders but may not have been able to capture all of the factors that could influence sleep time and quality, and also separately influence susceptibility to infection. These could include, for example, long working hours, family commitments, and physical or mental health problems.
Few people were included in the study, and as a result, the confidence intervals around the risk estimates are wide (for example, 1.08 to 18.69). This suggests uncertainty around the exact size of the risk, so we cannot be sure the risk is as greatly increased as it appears.
Some outcomes were self-reported and this is prone to bias. However, these outcomes were also objectively assessed using actigraphy, and this adds strength to the study.
It's also worth noting that the study only recruited from one area and did not include children or older adults, so we do not know whether the results would be generalisable to other populations.
Overall, the results do support the importance of good sleep. However, this may be affected by many factors, such as stress levels, lifestyle and family life. There are a range of things you can do to help you get to sleep, such as:
- avoiding caffeine later in the day
- avoiding heavy meals late at night
- setting regular times to wake up
- using thick curtains or blinds, an eye mask and earplugs to stop you being woken up by light and noise