Lead author Katrin Ackermann, a post-doctoral researcher at the Eramus MC University Medical Center in Rotterdam, the Netherlands, and colleagues at the University of Surrey said if the study findings were confirmed using more data, they would have implications for clinical practice and for professions associated with shift work.
The researchers compared the white blood cell counts of 15 healthy young men under normal and severely sleep-deprived conditions.
The greatest changes were seen in the white blood cells known as granulocytes, which showed a loss of day-night rhythmicity, along with increased numbers, particularly at night.
In the study, white blood cells were categorized and measured from 15 young men following a strict schedule of 8 hours of sleep every day for a week. The participants were exposed to at least 15 minutes of outdoor light within the first 90 minutes of waking and prohibited from using caffeine, alcohol or medication during the final three days to stabilize their circadian clocks and minimize sleep deprivation.
White blood cell counts in a normal sleep/wake cycle were compared to the numbers produced during the second part of the experiment, in which blood samples were collected after 29 hours of continual wakefulness.
The study, published in the journal Sleep, found the white blood cells reacted immediately to the physical stress of sleep loss and directly mirrored the body's stress response.