Sleep and the Immune System
Scientific evidence is building that sleep has powerful effects on immune functioning.4 Studies show that sleep loss can affect different parts of the immune system, which can lead to the development of a wide variety of disorders (see Figure 2.2 on the next page).
For example, a modest amount of sleep loss (restricting the time allowed for sleep to 4 hours for one night) reduced natural killer (NK) cell activity to an average of 72%, compared with NK cell activity in participants who had a full night's sleep (Figure 2.2, arrow 1).5 Research indicates that NK cells have a substantial role in killing tumor cells. Reduced functioning of NK cells was associated with a 1.6 times higher risk of dying with cancer (all sites) in an 11-year follow-up survey.6
In a similar way, restricting sleep to 4 hours for one night led to the generation of inflammatory cytokines, which play an important role in the development of cardiovascular and metabolic disorders (Figure 2.2, arrow 2).7
Sleep loss is also related to a higher risk for infection. Restricting sleep to 4 hours per night for 6 days, followed by sleep for 12 hours per night for 7 days, resulted in a greater than 50% decrease in production of antibodies to influenza vaccination, in comparison with subjects who had regular sleep hours (Figure 2.2, arrow 3).8
Inflammatory cytokines are protein molecules secreted by immune and other types of cells that signal other cells to promote inflammation.