Last Updated: 2009-01-12 16:00:35 -0400 (Reuters Health)

Poor sleep efficiency and reduced sleep duration increase the likelihood of developing a clinical cold following rhinovirus exposure, investigators report in the Archives of Internal Medicine for January 12.

"Experimental studies have demonstrated that sleep deprivation results in poorer immune function, such as reduced natural killer cell activity, suppressed interleukin-2 production, and increased levels of circulating pro-inflammatory cytokines," Dr. Sheldon Cohen, at Carnegie Mellon University, Pittsburgh, and co-investigators explain. However, there is little direct evidence to back up the theory that sleep quality affects susceptibility to illness.

In the current prospective study, 153 subjects, ages 22 to 55 years, were interviewed daily for 14 consecutive days regarding their sleep duration the previous night; sleep efficiency—defined as percentage of time in bed actually asleep—and whether or not they felt rested.

Afterwards, subjects were quarantined and nasal drops containing a rhinovirus were administered.

Over the next 5 days, 135 subjects became infected. Fifty-four had objective evidence of a cold, defined by mucus weight and nasal mucociliary clearance function. Sixty-six had subjective symptoms of congestion, sneezing, runny nose, earache, sinus pain, sore throat, and/or cough.

The average sleep duration and sleep efficiency were associated with an increased likelihood of developing an objectively defined cold, whereas "feeling rested" was not.

The association was strongest for sleep efficiency. Compared with the top tertile of average sleep efficiency (> 98%), the lowest tertile (< 92%) and the middle tertile (92% to 98%) were associated with odds ratios of 5.50 and 3.94, respectively, for objectively defined colds.

Corresponding odds for tertiles of sleep duration were 2.94 and 1.63, where the lowest tertile for sleep duration was less than 7 hours of sleep, and the highest was 8 or more hours.

Sleep efficiency was also significantly associated with total symptom score (p < 0.001).

Dr. Cohen’s group found that the associations were robust after adjustment for sociodemographics, prechallenge viral-specific antibody titers, season of the year, psychological factors and health practices.

These data support 7 to 8 hours of sleep as "a reasonable target," the authors conclude. However, "even a minimal habitual sleep disturbance (sleep losses of 2% to 8%, 10 to 38 minutes for an 8-hour sleeper) is associated with 3.9-times the risk of developing a cold."

Arch Intern Med 2009;169:62-67.