Poor Sleep Linked To More Colds

US researchers found that people who slept fewer than seven hours a night, and who spent more of that time awake, were nearly three times more likely to develop a cold than people who had eight hours or more of undisturbed sleep.

The study was the work of Dr Sheldon Cohen, of the Department of Psychology at Carnegie Mellon University in Pittsburgh, Pennsylvania, and colleagues, and was published in the 12 January issue of the Archives of Internal Medicine.

Poor sleep is thought to be a predictor of low immunity, and thereby more readily predisposing people to the common cold, although there is no direct evidence tying sleep quality in the weeks leading up to exposure to the risk of infection. The researchers said that studies had also shown that people who slept between seven and eight hours per night had the lowest rates of heart disease, illness and early death.

For this study, which took place between 2000 and 2004, Cohen and colleagues examined the links between sleep quality and sleep duration in the weeks leading up to being exposed to a cold virus, to the susceptibility to catching it.

The researchers recruited 153 healthy male and female volunteers aged 21 to 55 years and interviewed them every day for fourteen days to find out how long they had slept the previous night, how efficient their sleep had been, that is what percentage of the time in bed was actually spent sleeping, and whether they felt rested. The researchers then worked out the average quantities of sleep duration and sleep efficiency for each person for the 14 nights.

The volunteers then went into quarantine and took nasal drops containing the common cold virus (rhinovirus). They were kept under close observation for signs of a cold during the day before their exposure and for 5 days afterwards. They also gave mucus samples during this observation period, which were tested for virus cultures, and 28 days or so later they gave a blood sample that was tested for antibody response to the cold virus.

Before the 14 days of monitoring, each participant also underwent a "pre-challenge" examination, where the researchers obtained information about potential confounders such as virus-specific antibody levels in their blood, demographics, body mass index, psychological variables and health behaviours.

The results showed that:

• The less a person slept, the more likely he or she was to develop a cold (there was a graded association between infection rate and average sleep duration).
• Participants who slept fewer than 7 hours were 2.94 times more likely to develop a cold than those who had 8 hours or more sleep.
• The more efficiently a person slept (more of the time in bed actually spent asleep), the less likely he or she was to develop a cold (i.e. there was also a graded association between sleep efficiency and rate of infection).
• Participants whose sleep efficiency feel below 92 per cent were 5.50 times more likely to develop a cold than those whose efficiency was 98 per cent or more.
• Feeling rested was not linked to rate of infection.
• These relationships could not be explained by the potential counfounders such as levels of virus-specific antibodies beforehand, demographics, the season of the year, body mass index, socioeconomic status, health behaviours, and psychological variables.

Cohen and colleagues concluded that:

"Poorer sleep efficiency and shorter sleep duration in the weeks preceding exposure to a rhinovirus were associated with lower resistance to illness."

The researchers also looked at separate components of illness and how they linked to the variables they measured.

"When the components of clinical illness (infection and signs or symptoms) were examined separately, sleep efficiency but not sleep duration was associated with signs and symptoms of illness," they wrote, but "neither was associated with infection."

"A possible explanation for this finding is that sleep disturbance influences the regulation of pro-inflammatory cytokines, histamines and other symptom mediators that are released in response to infection," they suggested, recommending that seven to eight hours sleep a night would appear to be a reasonable target.

The editors noted that the study was supported by the National Heart, Lung and Blood Institute, by the National Institute of Allergy and Infectious Diseases and by supplementary funds provided by the John D. and Catherine T. MacArthur Foundation Network on Socioeconomic Status and Health.

Sleep Habits and Susceptibility to the Common Cold."
Sheldon Cohen; William J. Doyle; Cuneyt M. Alper; Denise Janicki-Deverts; Ronald B. Turner.
Archives of Internal Medicine Vol. 169, No. 1, pp 62-67, January 12, 2009.