Sunday, January 27, 2019

 Stress and the Immune System

How the immune system responds to stress depends on the time of day


What was the research about?
Forty-two undergraduate students participated in the study. The participants either did mental arithmetic (i.e., stressful task) or read magazines (i.e., nonstressful task) at either 8 AM or 2 PM. Blood samples were taken from each participant before the task, 2 minutes after beginning the task, and 60 and 90 minutes after completing the task.
The results showed that time of day mattered, but only after the stressful task. Compared to the nonstressful task, the number of natural killer cells during the stressful task were higher, regardless of the time of day. The elevated number of natural killer cells for those who had completed the stressful task at 8 AM remained elevated 60 and 90 minutes afterwards. For those who had completed the stressful task at 2 PM, however, the elevated number of natural killer cells 60 and 90 minutes afterwards dropped to less than before the task. Thus, although natural killer cells increased in number during the stressful task, afterwards, they remained higher if it was completed in the morning but dropped lower than they were to begin with if it was completed in the afternoon.
Why should it matter to me?
If possible, people should try to get stressful tasks out of the way in the morning. In this way, the immune system would be in better, instead of worse, shape for a short while after stressful tasks.
Source: Delahanty, D. L., Wang, T., Maravich, C., Forlenza, M., & Baum, A. (2000). Time-of-day effects on response of natural killer cells to acute stress in men and women. Health Psychology, 19, 39-45.