The role of blood glucose availability and fatigue in the development of cognitive impairment during combat training.

INTRODUCTION: The aim of this study was to determine whether inadequate nutrition would produce a reduction in the blood glucose concentration and impair cognitive function.

METHODS: Energy intake, blood glucose, and cognitive function were measured in 18 male subjects during a 4-d military field exercise. Baseline measures of fasting blood glucose, body mass, cognitive function, and mood were taken before the start of combat training. Measurements of blood glucose, cognition, and well-being were then repeated during every subsequent 24 h period. Activity levels were monitored continuously using wrist-worn activity monitors.

RESULTS: Subjects experienced an increase in symptoms relating to hypoglycemia after 24 h in the field (p < 0.01), vigor decreased (p < 0.001), and fatigue increased (p < 0.001). After 48 h, subjects reported feelings of depression (p < 0.05), anger (p < 0.01), and confusion (p < 0.001). Delayed memory recall was significantly impaired after 48 h (p < 0.05), and there was a decrease in vigilance (p < 0.01). Between 48 and 72 h, there was a decrease in immediate memory recall (p < 0.05). Delayed memory recall and vigilance remained impaired, but did not deteriorate further. When subjects were extracted from the field after 96 h, nude BM had decreased by 2% (p < 0.05).

CONCLUSION: Although it was possible to reproduce the symptoms and cognitive impairment associated with hypoglycemia, there was no change in blood glucose concentration throughout the 4-d period. The impairment in cognitive function is likely to have been the result of significant sleep deprivation.