Watch out for stress­ful sit­u­a­tions in the evening

The Borneo Post - Nature and health - - Front Page -

STRESS in the evening may take more of a toll on your body than stress at other times of day, a new study sug­gests. The rea­son? Later in the day, the hu­man body re­leases lower lev­els of the hor­mone that helps ease stress, ac­cord­ing to re­searchers from Ja­pan. “Our study sug­gests a pos­si­ble vul­ner­a­bil­ity to stress in the evening,” said study leader Yu­jiro Ya­manaka, a med­i­cal phys­i­ol­o­gist at Hokkaido Univer­sity in Sap­poro.

“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,” Ya­manaka said in a univer­sity news re­lease. The re­searchers mea­sured lev­els of the stress hor­mone cor­ti­sol in the saliva of 27 young, healthy

vol­un­teers. They also exposed them to a stress­ful sit­u­a­tion to see if the hy­potha­la­mic-pi­tu­itary-adrenal (HPA) axis re­sponds dif­fer­ently to acute stress at dif­fer­ent times of day.

The HPA axis con­nects the body’s cen­tral ner­vous and en­docrine sys­tems. When a stress­ful event ac­ti­vates the axis, the body re­leases cor­ti­sol. Cor­ti­sol lev­els are also con­trolled by the cir­ca­dian clock in the brain. The vol­un­teers were di­vided into two groups. One group was exposed to a stress test in the morn­ing, two hours af­ter wak­ing up. The other group was exposed to a stress test in the evening, af­ter be­ing awake for 10 hours.

The 15-minute test in­volved pre­par­ing and giv­ing a

pre­sen­ta­tion to three in­ter­view­ers and a cam­era. Par­tic­i­pants also had to do men­tal arith­metic. The re­searchers took saliva sam­ples half an hour be­fore the test, im­me­di­ately af­ter, and at 10-minute in­ter­vals for an­other half hour. Cor­ti­sol lev­els in­creased sig­nif­i­cantly in the morn­ing, but not in the evening, the re­sults showed.

How­ever, par­tic­i­pants’ heart rates – an in­di­ca­tor of the sym­pa­thetic ner­vous sys­tem’s re­sponse to stress – did not dif­fer. “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,” Ya­manaka said. The re­port was pub­lished in Neu­ropsy­chophar­ma­col­ogy Re­ports.

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