Tyrosine supplementation mitigates working memory decrements during cold exposure.

In rats, dietary supplementation with the amino acid tyrosine (TYR) prevents depletion of central catecholamines observed during acute environmental stress. Concomitant changes in the animals' behavioral responses to stress suggest that TYR might have similar effects on central catecholamines and cognition in humans exposed to environmental stress. This study aimed to determine if severe cold exposure impairs human cognition and if dietary supplementation with TYR would ameliorate such deficits. Volunteers (N=19) completed three test sessions on different days (35 degrees C control/placebo, approximately 10 degrees C/placebo, approximately 10 degrees C/TYR) using a double-blind, within subjects design. During each session, volunteers completed two 90-minute water immersions and consumed a food bar (150 mg/kg TYR or placebo) before each immersion (total TYR 300 mg/kg). Cognitive performance, mood, and salivary cortisol were assessed. Cortisol was elevated in the cold (p<.01). Volunteers made fewer correct responses on a Match-to-Sample memory measure (p<.05) and reaction time (RT) and errors increased on a choice RT test (p<.01) in the cold. Self-reported tension (p<.01), depression (p<.05) and confusion (p<.01) also increased in the cold. When volunteers consumed TYR, correct responses increased on a Match-to-Sample memory measure (p<.05) and study time for the sample was shorter (p<.05), indicative of more rapid and accurate information processing. Finally, RT on the memory measure revealed a similar pattern across immersions for TYR and thermoneutral conditions, but not cold/placebo (p<.05). This study demonstrates cold exposure degrades cognitive performance and supplementation with TYR alleviates working memory decrements.

Field assessment and enhancement of cognitive performance: development of an ambulatory vigilance monitor.

INTRODUCTION: Limited opportunities to study human cognitive performance in non-laboratory, ambulatory situations exist. However, advances in technology make it possible to extend behavioral assessments to the field. One of the first devices to measure human behavior in the field was the wrist-worn actigraph. This device acquires minute-by-minute information on an individual's physical activity and can distinguish sleep from waking, the most basic aspect of behavior. METHODS: Our laboratory developed a series of wrist-worn devices, not much larger than a watch, which assess reaction time, vigilance and memory. The devices concurrently assess motor activity with greater temporal resolution than standard actigraphs. They also continuously monitor multiple environmental variables including temperature, humidity, sound, and light. RESULTS: These monitors have been employed during training and simulated military operations to collect behavioral and environmental information that would typically be unavailable under such circumstances. Development of the vigilance monitor, and how each successive version extended capabilities of the device are described. Data from several studies are presented, including studies conducted in harsh field environments during a simulated infantry assault, an officer training course. DISCUSSION: The monitors simultaneously documented environmental conditions, patterns of sleep and activity and effects of nutritional manipulations on cognitive performance. They provide a new method to relate cognitive performance to real world environmental conditions and assess effects of various interventions on human behavior in the field. They can also monitor cognitive performance in real time, and if it is degraded, attempt to intervene to maintain

Severe decrements in cognition function and mood induced by sleep loss, heat, dehydration, and undernutrition during simulated combat.

BACKGROUND: Military exercises generate high levels of stress to simulate combat, providing a unique opportunity to examine cognitive and physiologic responses of normal humans to acute stress. METHODS: Cognitive and physiologic markers of stress were evaluated before, during, and after an intense training exercise conducted for 53 hours in the heat. Cognitive performance, mood, physical activity, sleep, body composition, hydration, and saliva cortisol, testosterone, and melatonin were assessed. Volunteers were 31 male U.S. Army officers from an elite unit, aged 31.6 +/- .4 years. RESULTS: Wrist activity monitors documented that soldiers slept only 3.0 +/- .3 hours during the exercise and were active throughout. Volunteers lost 4.1 +/- .2 kg (p < .001) of weight, predominately water (3.1 +/- .3 L) (p < .001). Substantial degradation in cognitive function, assessed with computerized tests, occurred. Vigilance, reaction time, attention, memory, and reasoning were impaired (p < .001). Mood, including vigor (p < .001), fatigue (p < .001), confusion (p < .001), depression (p < .001), and tension (p < .002), assessed by questionnaire, deteriorated. The highest cortisol and testosterone levels were observed before the exercise. CONCLUSIONS: This study quantifies the overwhelmingly adverse impact of multiple stressors on cognitive performance, mood, and physiologic parameters, during a continuous but brief military exercise conducted by highly motivated, well-trained officers.

Lipid and other plasma markers are associated with anxiety, depression, and fatigue.

OBJECTIVE: Few peripheral metabolites have been shown to be associated with mood in healthy individuals or patients with central nervous system diseases. During military basic combat training (BCT), mood state, physical performance and body composition substantially improve, providing an opportunity to examine relationships between mood and nutritional and hormonal biomarkers. METHOD: Thirty-five females enrolled in U.S. Marine BCT, an intense physically and mentally challenging 12-week course, were studied. Every 4 weeks, mood was assessed with the Profile of Mood States (POMS), as were nutritional, metabolic and hormonal plasma markers. RESULTS: Mood and fitness improved over BCT, and there were substantial changes in biochemical markers. Multiple regression demonstrated that, in combination, cholesterol (HDL, LDL), fructosamine, triglycerides, free fatty acids (FFA), dehydroepiandrosterone-sulfate (DHEA-S), ACTH, and substance P accounted for 44% of variation in anxiety, 40% confusion, 37% fatigue, 27% depression and 40% in total mood (p < .0001). Increased HDL, FFA, DHEA-S, and substance P were associated with degraded mood (p < .05). Increased LDL, triglycerides, fructosamine, and ACTH were associated with improved mood (p < .05). Other markers, including glucose, cortisol, and C-reactive protein were not associated with mood. CONCLUSIONS: Normal human mood state was associated with 8 plasma markers. Increased HDL and lower LDL, which are associated with improved cardiovascular status, were associated with negative affect. Fructosamine and substance P, not previously known to be related to mood, were associated with it. We are not aware of any biological parameters that in aggregate predict such a substantial proportion of variation in normal mood.

Appetite and endocrine regulators of energy balance after 2 days of energy restriction: insulin, leptin, ghrelin, and DHEA-S.

Using a double-blind, placebo-controlled crossover design, the effects of 48 h near complete energy restriction on endocrine regulators of appetite and satiety were assessed. Twelve men and one woman participated in this controlled, 2-day diet intervention study. One experimental trial was completed in a calorie deprived state (CAL-DEP; <10% of estimated energy requirements) and others in a fed condition (carbohydrate only and carbohydrate and fat; data were pooled and compared to CAL-DEP). Test meals containing prescribed energy intake and indistinguishable in sensory characteristics were provided during each trial. Glucose, insulin, leptin, ghrelin, cortisol, dehydroepiandrosterone-sulfate (DHEA-S), and satiety were repeatedly assessed. Mean glucose, insulin, and leptin concentrations were lower (P < 0.0001) for CAL-DEP compared to the fully fed (FED) state. Ghrelin and DHEA-S were higher (P < 0.0001) for CAL-DEP relative to FED. Cortisol levels declined each day regardless of diet (P < 0.0001) but were 32% higher (P < 0.01) at the conclusion of the session for CAL-DEP compared to FED. Satiety was 25% lower (P < 0.0001) for CAL-DEP relative to FED and decreased (P < 0.0001) over time regardless of diet. In the FED state, insulin (r = 0.55), glucose (r = 0.76), cortisol (r = -0.59), and DHEA-S (r = -0.62) were associated (P < 0.05) with satiety, but not during CAL-DEP. These findings show that 2 days of severe energy restriction alter several endocrine regulators of appetite independent of perception of increased hunger suggesting a physiological mechanism to explain overeating following acute periods of severe energy restriction.

A double-blind, placebo-controlled test of 2 d of calorie deprivation: effects on cognition, activity, sleep, and interstitial glucose concentrations.

BACKGROUND: Anecdotal information and limited research suggest that short-term caloric deprivation adversely affects cognition. However, this issue has not been studied using double-blind, placebo-controlled procedures, because the formulation of a calorie-deficient feeding regimen identical to one with calories is impossible using ordinary foods. Therefore, test meals varying in caloric content, but indistinguishable in sensory characteristics, were formulated using hydrocolloid-based gels as the principal structural component. OBJECTIVE: The purpose of this study was to examine the effects of 2 d of near-total caloric deprivation on cognitive function, satiety, activity, sleep, and glucose concentrations in a controlled environment. DESIGN: A double-blind, placebo-controlled crossover study of caloric deprivation was conduced in a controlled environment for 48 h. Cognitive function in 27 healthy young subjects was assessed repeatedly with standardized tests of vigilance, reaction time, learning, memory, logical reasoning, mood, and satiety. Wrist-worn monitors were used to assess ambulatory vigilance, activity, and sleep. Interstitial glucose concentrations were assessed continuously with a minimally invasive monitor. RESULTS: When the subjects received the near calorie-free diets, mean calorie consumption totaled 1311 kJ (313 kcal) over the testing period. During the fully fed treatment sessions, the subjects consumed a mean of 9612 kJ/d (2294 kcal/d), which matched their individual, daily energy requirements. Satiety and interstitial glucose concentrations were lower during the calorie-deprived diet (P < 0.001) than during the fully fed diet. There were no detectable effects of calorie deprivation on any aspect of cognitive performance, ambulatory vigilance, activity, or sleep. The mood states assessed, including fatigue, were not affected by calorie deprivation. CONCLUSIONS: Cognitive performance, activity, sleep, and mood are not adversely affected in healthy humans by 2 d of calorie-deprivation when the subjects and investigators are unaware of the calorie content of the treatments.

Food acceptability in field studies with US army men and women: relationship with food intake and food choice after repeated exposures.

Laboratory data with single exposures showed that palatability has a positive relationship with food intake. The question addressed in this study is whether this relationship also holds over repeated exposures in non-laboratory contexts in more natural environments. The data were collected in four field studies, lasting 4-11 days with 307 US Army men and 119 Army women, and comprised 5791 main meals and 8831 snacks in total. Acceptability was rated on the nine point hedonic scale, and intake was registered in units of 1/4, 1/2, 3/4, or 1 or more times of the provided portion size. Correlation coefficients between individual acceptability ratings and intakes varied from 0.22 to 0.62 for the main meals (n=193-2267), and between 0.13 and 0.56 for the snacks (n=304-2967). The likelihood of choosing a meal for the second time was positively related to the acceptability rating of the meal when it was consumed for the first time. The results reinforce the importance of liking in food choice and food intake/choice behavior. However, the magnitude of the correlation coefficients between acceptability ratings and food intake suggest that environmental factors also have an important role in determining intake and choice.