Study: Evening stress may be worse than morning stress
Tuesday, December 04, 2018
The Decade of the Brain, as proclaimed by President George H.W. Bush for the 1990s, has come and gone. But many mysteries remain, and President Barack Obama launched his own brain research program in 2013 — The Brain Research Through Advancing Innovative Neurotechnologies (BRAIN) Initiative.
The fact that the brain inspired such a call to action is not surprising in view of the many mysteries still to be revealed.
This three-pound organ, enclosed in the skull, contains a multitude of processes, and so many of the basic ones continue to elude our understanding. But researchers continue their commitment to the scientific investigation of this enigmatic and compelling organ.
A study published earlier this year, conducted by researchers at the National Institute of Mental Health (NIMH), revealed more about the organization and function of a brain structure, the paraventricular nucleus of the thalamus (PVT) that may serve a key role in linking stress detection to the development of adaptive behaviors. The (PVT) is a brain structure that has been identified as a player in emotional processing, learning, and in adaptive responses to stress.
It has been reported that most Americans are suffering from moderate to high stress, with 44 percent stating that their stress levels had increased over the previous five years. Concerns about money, work and the economy top the list of most frequently cited sources of stress.
Fears about job stability are on the rise, with 49 percent of respondents citing such fears as a source of stress — up from 44 percent during the previously measured year. Coping with stress has become increasingly important to avoid becoming chronically fatigued or depressed.
A recent study found that stressful events in the evening release less of the body’s stress hormones than those that happen in the morning, suggesting that evening stress may leave us more vulnerable.
In this study, Yujiro Yamanaka, a medical physiologist, and his colleagues at Japan's Hokkaido University recruited 27 young, healthy volunteers with normal work hours and sleep habits to find out if the hypothalamic-pituitary-adrenal (HPA) axis, which connects the central nervous and endocrine systems of the body responds differently to acute psychological stress according to the time of day.
The primary stress hormone cortisol is released for several hours when the HPA axis is activated by a stressful event, a process that 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.
To first establish a baseline, the researchers measured the diurnal rhythm of salivary cortisol levels of the volunteers. Then, the volunteers were then divided into two groups.
One group was exposed to a stress test (15 minutes) in the morning, two hours after their normal waking time. The second group was exposed to the same stress test in the evening, ten hours after their normal waking time.
The test included preparing and giving a presentation in front of three trained interviewers and a camera and conducting a mental arithmetic. Saliva samples were obtained half an hour before starting the test, immediately after, and at 10-minute intervals for another half hour.
The results showed that salivary cortisol levels increased significantly in the volunteers who took the stress test in the morning. Those who took the evening stress test showed no response. The volunteers' heart rates, an indicator of the sympathetic nervous system that immediately responds to stress, did not differ according to when the test was taken.
According to Yujiro Yamanaka, 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. Although the study suggests a possible vulnerability to stress in the evening, it is important to consider each individual’s unique biological clock and time of day when assessing the response to stressors and preventing them.
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