People who get less than seven hours of sleep per night appear about three times as likely to develop respiratory illness following exposure to a cold virus as those who sleep eight hours or more.
Experimental studies have demonstrated that sleep deprivation results in poorer immune function. However, there is little direct evidence to back up the theory that sleep affects susceptibility to illness.
Researchers from America interviewed 153 men and women (age range, 21-55 years) daily for 14 consecutive days regarding how many hours they slept per night, what percentage of their time in bed was spent asleep and whether they felt rested. The study subjects were then quarantined and administered nasal drops containing the common-cold-causing rhinovirus.
It was found that the less an individual slept, the more likely he or she was to develop a cold. Lower sleep efficiency was also associated with developing a cold - men and women who spent less than 92 percent of their time in bed asleep were five and a half times more likely to become ill than those whose sleep efficiency was 98 percent or more. Feeling rested was not associated with colds.
The above data supports seven to eight hours of sleep as a reasonable target. However, even a minimal habitual sleep disturbance (sleep losses of 2 percent to 8 percent, 10 to 38 minutes for an 8-hour sleeper) is associated with 4 times the risk of developing a cold.
