While no one likes dealing with stress, our bodies are equipped with special hormones and mechanisms to help us cope with it. A stressful event triggers the release of cortisol which is the primary stress hormone in humans that helps increase energy levels in the face a fight or flight response.
But now, a new study has found that stress in the evening releases less cortisol compared to stressful events in the morning.
The study was conducted by researchers from the Hokkaido University in Japan and published in the journal Neuropsychopharmacology Reports.
The results suggest that we may be more vulnerable to the negative impacts of stress in the evening because our bodies stress response is dampened.
To better understand the link between stress and time of day, the researchers focused on the hypothalamic-pituitary-adrenal (HPA) axis and its differing responses in 27 volunteers.
The HPA axis connects the central nervous system and the endocrine system (the hormone system). When the HPA axis reacts to a stressful event, the endocrine system floods the body with cortisol, and the body’s internal clock regulates cortisol levels throughout the day.
The 27 volunteers for the study all had normal work and sleep schedules, and the researchers measured cortisol levels by analyzing saliva samples both before and after a stressful event.
The participants were split into two groups, and one group had a stress test in the morning while the other had the test in the evening.
For the test, the participants had to give a presentation and do math problems in their head. The researchers took saliva samples from the participants a half hour before the test, after the test, and during ten-minute intervals for a half hour following the test.
Not surprisingly, cortisol levels spiked in the participants given the stress test in the morning. However, for the evening group, there were no recorded increases in cortisol.
“Our study suggests a possible vulnerability to stress in the evening,” said aid Yujiro Yamanaka, the lead author of the study. “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.”