Katie Heaney is the published author of Never Have I Ever and the upcoming novel Dear Emma. She is an editor at Buzzfeed and has written for New York Magazine and Pacific Standard, among other places. She is a graduate of Illinois Wesleyan University and the University of Minnesota. Dr. Patrick Borgen M.D.
I tend to experience the most stress between 6–8 p.m., which is weird, because that’s the one time of day I’m not working or sleeping, and am therefore, at least in theory, “relaxing.” I always assumed this had something to do with the lack of sunlight — resolution and change and growth still seem possible during the day, especially if it’s sunny, but at night? Everything seems closed off and pre-determined, and I always end up thinking about death. Ha.
Anyway, the sunlight thing may or may not be part of it, but apparently evening stress is actually worse than daytime stress, according to a new study published in the journal Neuropsychopharmacology Reports.
The authors, who conducted their research at Hokkaido University in Japan, tested how their 27 subjects’ hypothalamic-pituitary-adrenal (or HPA) axes responded to stress incurred at different times of day. The HPA axis connects the central nervous and endocrine systems, and its activation leads to the body’s release of cortisol, the primary human stress hormone. By measuring cortisol levels after a stressful event, the researchers could therefore determine how capably the human body responds to stress in the morning compared to the evening.
After establishing subjects’ baseline cortisol levels, they were asked to prepare and give a presentation to three trained interviewers and a camera, which I am stressed just thinking about. Saliva samples were taken before and immediately after each presentation, and at ten-minute intervals for half an hour afterward.
The authors also found that students who were given the stress test in the morning had significantly higher cortisol levels in their saliva, while those who were given the evening test experienced no such change. Conversely, there was no significant difference between the post-test heart rates measured in both groups, suggesting that the sympathetic nervous system may be less influenced by time.
I would have thought that a higher stress hormone count meant more stress, but it’s a little counterintuitive, kind of in the same way having a high white blood cell count is actually bad, even though white blood cells are good, because it means something is wrong.
If we think of cortisol level as one of the body’s strongest tools in addressing stress, its heightened presence is actually (usually) a good thing. Lead author Yujiro Yamanaka explains his study’s findings as follows: in the morning, our bodies have both the HPA axis and our sympathetic nervous system at their disposal, while in the evenings, they have only the latter (in the form of elevated heart rate, for instance).
While Yamanaka concedes there is some room for variation due to individuals’ biological clocks (cortisol production also being reliant, in part, on circadian rhythms), generally speaking, he says, his findings suggest “a possible vulnerability to stress in the evening.” To which I say, no kidding!
Stressful events in the evening release less of the body’s stress hormones than those that happen in the morning, suggesting possible vulnerability to stress in the evening.
The body’s central system also reacts less strongly to acute psychological stress in the evening than it does in the morning, according to research conducted at Japan’s Hokkaido University.In the study published in the journal Neuropsychopharmacology Reports, medical physiologist Yujiro Yamanaka and his colleagues recruited twenty- seven young, healthy volunteers with normal work hours and sleep habits to find out if the “hypothalamic -pituitary-adrenal” (HPA) axis responds differently to acute psychological stress according to the time of day.
The HPA axis connects the central nervous and endocrine systems of the body. Cortisol, the primary stress hormone in humans, is released for several hours when the HPA axis is activated by a stressful event. This helps provide the body with energy in the face of a perceived need for fight or flight. Cortisol levels are also regulated by a master circadian clock in the brain, and are normally high in the morning and low in the evening.
The team first measured the diurnal rhythm of salivary cortisol levels from volunteers to establish a baseline. The volunteers were then divided into two groups: one that was exposed to a stress test in the morning, two hours after their normal waking time, and another that was exposed to a stress test in the evening, ten hours after their normal waking time.
The test lasted for a period of 15 minutes and involved preparing and giving a presentation in front of three trained interviewers and a camera, and conducting a mental arithmetic. Saliva samples were taken half an hour before starting the test, immediately after, and at ten-minute intervals for another half hour.
The researchers found that salivary cortisol levels increased significantly in the volunteers that took the stress test in the morning while no such response was observed in those that took the test in the evening. The volunteers’ heart rates on the other hand, an indicator of the sympathetic nervous system which immediately responds to stress, and did not differ according to when the test was taken.
Yujiro Yamanaka commented “The body can respond to the morning stress event by activating the HPA axis and sympathetic nervous system, but it needs to respond to evening stress event by activating the sympathetic nervous system only. Our study suggests a possible vulnerability to stress in the evening. However, it is important to take into account each individual’s unique biological clock and the time of day when assessing the response to stressors and preventing them.”
Journal Reference:
Yujiro Yamanaka, Hidemasa Motoshima, Kenji Uchida. Hypothalamic-pituitary- adrenal axis differentially responses to morning and evening psychological stress in healthy subjects. Source: https://onlinelibrary.wiley.com/