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A study published earlier this month in the journal Archives of Internal Medicine made headlines recently. Researchers report that people experiencing poor sleep and shorter nights sleeping following exposure to the common cold are more likely to get sick than those that get better rest . Scientists suggest that lack of sleep may influence the regulation of symptom mediators such as proinflammatory cytokines (signaling molecules) and histamines that are released in response to infection.
Carnegie Mellon University researchers evaluated 153 healthy men and women between 2000 and 2004. Participants were given nasal drops containing a high dose of rhinovirus, which causes the common cold (125 times the dose necessary to infect 50% of tissue cultures exposed to the virus). Prior to viral exposure, the level of serum antibody to the virus was measured in participants. Those participants with high titers (meaning levels) and thus increased resistance to infection were excluded from the study.
Participants were interviewed by phone on 14 consecutive evenings. The first interview occurred 20 to 23 days before viral exposure. Participants were asked the following questions:
- What time did you lie down to go to sleep last night?
- What time did you get out of bed this morning?
- How many minutes of sleep did you lose between the time you lay down to go to sleep and the time you got out of bed because you had difficulty falling asleep or you woke up and could not get back to sleep?
- Did you spend any time in bed between lying down to go to sleep and getting out of bed intentionally awake (e.g. reading or watching television)? If yes, for how many minutes?
- Did you feel rested from your sleep when you awoke this morning (yes or no)?
Sleep scores were calculated for each interview. Duration of sleep was scored as the number of hours slept (from the time the participant lay down to go to sleep until the time he or she got out of bed minus the minutes of sleep lost minus the minutes he or she was intentionally awake). Sleep efficiency was scored as sleep duration divided by time in bed (from the time the participant lay down until the time he or she got out of bed). Researchers then averaged scores across the 14 days to generate the average sleep duration, the average sleep efficiency and the percentage of days that participants felt rested.
The study controlled for viral immunity (levels of serum antibody prior to viral exposure), age, body mass, race, income, education, sex, season of exposure, psychological variables previously found to be associated with risk for colds (i.e. perceived social status, perceived stress, positive emotional style, extraversion and agreeableness [2-4]), smoking rate, alcohol consumption and physical activity.
Following viral exposure, participants were quarantined in separate rooms and monitored for 5 days to assess infection and signs and symptoms of illness. Of the 153 subjects, 135 (88.2%) became infected with the virus. However, not all those people got sick; 54 (35.4%) developed a cold based on objective measures while 66 (43.1%) developed a cold based on self-reports. When control variables included age, viral-specific antibody titer and sleep habits (reports of sleep duration, efficiency and “feeling rested” across the 14 consecutive days prior to virus exposure), both lower sleep efficiency (i.e. the percentage of time in bed asleep) and shorter sleep duration were associated with increased risk for the development of a cold.
In terms of sleep efficiency, participants who spent less than or equal to 92% of their time in bed asleep were five and a half times more likely to get sick than those who spent greater than or equal to 98% of their time in bed asleep. In terms of sleep duration, individuals with less than 7 hours of sleep were approximately three times more likely to develop a cold than those with 8 hours or more of sleep. With modern day distractions such as late night TV and the Internet, chronic sleep loss and sleep disorders are common problems. Indeed, 10% of adults report insufficient rest or sleep every day.
This study is subject to a number of limitations. Foremost is that it uses a survey, which is limited by validity and reliability. In fact, the authors caution that existing evidence suggests that self-reported sleep slightly underestimates both duration and total number of nocturnal wakenings. Moreover, since it is a descriptive method, a survey cannot offer insight into cause-and-effect relationships. The small sample size also limits the strength of the conclusions.
Nonetheless, the take home message is obvious: people that get better sleep get less sick than those that don’t. Indeed, this study suggests a substantial risk for susceptibility to the common cold when sleeping less than 7 hours per night.
How much sleep do you get at night?
Additional sleep disorder resources are listed in the Highlight HEALTH Web Directory.
- Cohen et al. Sleep habits and susceptibility to the common cold. Arch Intern Med. 2009 Jan 12;169(1):62-7. DOI: 10.1001/archinternmed.2008.505
- Cohen et al. Objective and subjective socioeconomic status and susceptibility to the common cold. Health Psychol. 2008 Mar;27(2):268-74.
- Cohen et al. Psychological stress and susceptibility to the common cold. N Engl J Med. 1991 Aug 29;325(9):606-12.
- Cohen et al. Positive emotional style predicts resistance to illness after experimental exposure to rhinovirus or influenza a virus. Psychosom Med. 2006 Nov-Dec;68(6):809-15. Epub 2006 Nov 13.