Natick Study Examines Effects of Stress on Soldiers' Immune Systems, Cognitive Ability

Pvt. Daniel Pardo dozes off after a period of sleep restriction in a study conducted by the U.S. Army Research Institute of Environmental Medicine to see how nutritional supplements might help wounds heal in warfighters under stress.

Training and operations can put such tremendous physical and psychological stresses on warfighters that their immune systems may be compromised.

A study being conducted by the U.S. Army Research Institute of Environmental Medicine, or USARIEM, at Natick Soldier Systems Center here, will examine how sleep restriction -- the stressor -- affects wound healing and whether nutritional supplements can help offset the effects. In a sub-study, the effect of sleep restriction on friend-foe recognition during marksmanship is also being observed.

"Immune responsiveness is suppressed in warfighters exposed to physical and psychological stress," said Tracey Smith, Ph.D., a research dietitian with USARIEM's Military Nutrition Division, who used Ranger School and Special Forces Assessment School as examples. "Research has shown that modest improvement in immune responsiveness, as determined from blood markers, was noted when Soldiers were provided a nutritionally fortified energy bar during Special Forces Assessment School."

Smith said the Special Forces research didn't focus on whether nutrition helped wounds to heal or defend against a virus, however.

"Immune markers measured from blood samples provide an indication of systemic immune response," said Smith, "but the systemic immune response does not necessarily reflect the functional status of the immune system -- for example, wound healing time."

In the study, male and female Soldiers were given suction blisters on their forearms. Some volunteers slept at least seven hours per night, and the current group is undergoing 50 hours of sleep restriction, with Soldiers allowed just two hours of sleep per night over that period.

"This was the amount of time that we thought would cause decrements in healing time and immune responsiveness at the wound site in young adults," Smith said. "This model may provide a way to more effectively study effects of stress on wound healing, and a means to test prototype countermeasures, like nutrition interventions, to stress-related effects on healing.

"We are using the suction blister model as a tool for studying immune responsiveness of warfighters coping with stress, and nutrition interventions to mitigate decrements in immune responsiveness caused by stress."

Capt. Adam Cooper, Ph.D., a research psychologist at USARIEM, piggybacked his marksmanship research on Smith's study.

"We are interested in how sleep restriction differentially affects marksmanship performance during a simple versus mentally challenging friend-foe task," Cooper said. "The factors we are examining are reaction time, accuracy and correct decision.

"Once it is known what factors are affected during low versus high mentally demanding marksmanship tasks, leaders can make more informed decisions concerning what types of missions their Soldiers will be able to successfully complete given their current state of rest."

Smith said that the marksmanship "keeps the volunteers awake, engaged and, hopefully, adds to the sleep restriction stressor."

The USARIEM study is using 60 volunteer Soldiers, split into groups of four per session. Smith and her colleagues will soon examine preliminary data from eight volunteers to see if the sleep restriction is an adequate stressor to slow healing time. Once they are confident with the stressor, they will move on to test nutrition interventions to promote immune recovery.

"Blister wounds typically heal in five days for volunteers who receive adequate sleep," Smith said. "We expect healing time to be delayed by one to two days in volunteers who are sleep restricted, and we expect that healing time will be back to five days in volunteers who consume a specially prepared nutrition beverage during sleep restriction and in the recovery period."

Smith and her colleagues hope to provide warfighters with a food item or beverage that they can consume during and after periods of stress that will support their immune system and promote recovery.

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